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Sandin SI, de Alba E. Quantitative Studies on the Interaction between Saposin-like Proteins and Synthetic Lipid Membranes. Methods Protoc 2022; 5:mps5010019. [PMID: 35200535 PMCID: PMC8878781 DOI: 10.3390/mps5010019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 01/28/2022] [Accepted: 01/31/2022] [Indexed: 12/05/2022] Open
Abstract
Members of the saposin-fold protein family and related proteins sharing a similar fold (saposin-like proteins; SAPLIP) are peripheral-membrane binding proteins that perform essential cellular functions. Saposins and SAPLIPs are abundant in both plant and animal kingdoms, and peripherally bind to lipid membranes to play important roles in lipid transfer and hydrolysis, defense mechanisms, surfactant stabilization, and cell proliferation. However, quantitative studies on the interaction between proteins and membranes are challenging due to the different nature of the two components in relation to size, structure, chemical composition, and polarity. Using liposomes and the saposin-fold member saposin C (sapC) as model systems, we describe here a method to apply solution NMR and dynamic light scattering to study the interaction between SAPLIPs and synthetic membranes at the quantitative level. Specifically, we prove with NMR that sapC binds reversibly to the synthetic membrane in a pH-controlled manner and show the dynamic nature of its fusogenic properties with dynamic light scattering. The method can be used to infer the optimal pH for membrane binding and to determine an apparent dissociation constant (KDapp) for protein-liposome interaction. We propose that these experiments can be applied to other proteins sharing the saposin fold.
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Affiliation(s)
- Suzanne I. Sandin
- Department of Bioengineering, School of Engineering, University of California Merced, Merced, CA 95343, USA;
- Chemistry and Biochemistry Ph.D. Program, University of California Merced, Merced, CA 95343, USA
| | - Eva de Alba
- Department of Bioengineering, School of Engineering, University of California Merced, Merced, CA 95343, USA;
- Correspondence:
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2
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Breiden B, Sandhoff K. Acid Sphingomyelinase, a Lysosomal and Secretory Phospholipase C, Is Key for Cellular Phospholipid Catabolism. Int J Mol Sci 2021; 22:9001. [PMID: 34445706 PMCID: PMC8396676 DOI: 10.3390/ijms22169001] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2021] [Revised: 08/14/2021] [Accepted: 08/16/2021] [Indexed: 02/06/2023] Open
Abstract
Here, we present the main features of human acid sphingomyelinase (ASM), its biosynthesis, processing and intracellular trafficking, its structure, its broad substrate specificity, and the proposed mode of action at the surface of the phospholipid substrate carrying intraendolysosomal luminal vesicles. In addition, we discuss the complex regulation of its phospholipid cleaving activity by membrane lipids and lipid-binding proteins. The majority of the literature implies that ASM hydrolyses solely sphingomyelin to generate ceramide and ignores its ability to degrade further substrates. Indeed, more than twenty different phospholipids are cleaved by ASM in vitro, including some minor but functionally important phospholipids such as the growth factor ceramide-1-phosphate and the unique lysosomal lysolipid bis(monoacylglycero)phosphate. The inherited ASM deficiency, Niemann-Pick disease type A and B, impairs mainly, but not only, cellular sphingomyelin catabolism, causing a progressive sphingomyelin accumulation, which furthermore triggers a secondary accumulation of lipids (cholesterol, glucosylceramide, GM2) by inhibiting their turnover in late endosomes and lysosomes. However, ASM appears to be involved in a variety of major cellular functions with a regulatory significance for an increasing number of metabolic disorders. The biochemical characteristics of ASM, their potential effect on cellular lipid turnover, as well as a potential impact on physiological processes will be discussed.
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Affiliation(s)
| | - Konrad Sandhoff
- Membrane Biology and Lipid Biochemistry Unit, LIMES Institute, University of Bonn, 53121 Bonn, Germany
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3
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Sandin SI, Gravano DM, Randolph CJ, Sharma M, de Alba E. Engineering of Saposin C Protein Chimeras for Enhanced Cytotoxicity and Optimized Liposome Binding Capability. Pharmaceutics 2021; 13:pharmaceutics13040583. [PMID: 33921905 PMCID: PMC8072984 DOI: 10.3390/pharmaceutics13040583] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Revised: 04/11/2021] [Accepted: 04/14/2021] [Indexed: 02/04/2023] Open
Abstract
Saposin C (sapC) is a lysosomal, peripheral-membrane protein displaying liposome fusogenic capabilities. Proteoliposomes of sapC and phosphatidylserine have been shown to be toxic for cancer cells and are currently on clinical trial to treat glioblastoma. As proof-of-concept, we show two strategies to enhance the applications of sapC proteoliposomes: (1) Engineering chimeras composed of sapC to modulate proteoliposome function; (2) Engineering sapC to modify its lipid binding capabilities. In the chimera design, sapC is linked to a cell death-inducing peptide: the BH3 domain of the Bcl-2 protein PUMA. We show by solution NMR and dynamic light scattering that the chimera is functional at the molecular level by fusing liposomes and by interacting with prosurvival Bcl-xL, which is PUMA’s known mechanism to induce cell death. Furthermore, sapC-PUMA proteoliposomes enhance cytotoxicity in glioblastoma cells compared to sapC. Finally, the sapC domain of the chimera has been engineered to optimize liposome binding at pH close to physiological values as protein–lipid interactions are favored at acidic pH in the native protein. Altogether, our results indicate that the properties of sapC proteoliposomes can be modified by engineering the protein surface and by the addition of small peptides as fusion constructs.
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Affiliation(s)
- Suzanne I. Sandin
- Department of Bioengineering, University of California, Merced, CA 95343, USA; (S.I.S.); (C.J.R.); (M.S.)
- Chemistry and Chemical Biology Ph.D. Program, University of California, Merced, CA 95343, USA
| | - David M. Gravano
- Stem Cell Instrumentation Foundry, University of California, Merced, CA 95343, USA;
| | - Christopher J. Randolph
- Department of Bioengineering, University of California, Merced, CA 95343, USA; (S.I.S.); (C.J.R.); (M.S.)
| | - Meenakshi Sharma
- Department of Bioengineering, University of California, Merced, CA 95343, USA; (S.I.S.); (C.J.R.); (M.S.)
| | - Eva de Alba
- Department of Bioengineering, University of California, Merced, CA 95343, USA; (S.I.S.); (C.J.R.); (M.S.)
- Correspondence:
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4
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Synthesis of Fluorescent Membrane-Spanning Lipids for Studies of Lipid Transfer and Membrane Fusion. Methods Mol Biol 2019; 1949:307-324. [PMID: 30790264 DOI: 10.1007/978-1-4939-9136-5_21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
For uncompromised in vitro assays for intermembrane lipid transfer and membrane fusion fluorescent membrane-spanning lipids have proved to be invaluable tools. These lipids in contrast to phosphoglycerolipids and sphingolipids are resistant to spontaneous as well as protein-mediated intermembrane transfer. Here I describe the synthesis of some homo-substituted fluorescent bipolar membrane-spanning lipids that bear a fluorescent tag either directly or via a phosphoethanolamine spacer to the lipid core. For the synthesis the lipid core of the bipolar membrane-spanning lipids, i.e., the tetraether lipid caldarchaeol, is prepared from cultures of the archaea Thermoplasma acidophilum.
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Abstract
Gangliosides are sialic acid containing glycosphingolipids, which are abundant in mammalian brain tissue. Several fatal human diseases are caused by defects in glycolipid metabolism. Defects in their degradation lead to an accumulation of metabolites upstream of the defective reactions, whereas defects in their biosynthesis lead to diverse problems in a large number of organs.Gangliosides are primarily positioned with their ceramide anchor in the neuronal plasma membrane and the glycan head group exposed on the cell surface. Their biosynthesis starts in the endoplasmic reticulum with the formation of the ceramide anchor, followed by sequential glycosylation reactions, mainly at the luminal surface of Golgi and TGN membranes, a combinatorial process, which is catalyzed by often promiscuous membrane-bound glycosyltransferases.Thereafter, the gangliosides are transported to the plasma membrane by exocytotic membrane flow. After endocytosis, they are degraded within the endolysosomal compartments by a complex machinery of degrading enzymes, lipid-binding activator proteins, and negatively charged lipids.
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Affiliation(s)
- Bernadette Breiden
- LIMES Institute, Membrane Biology & Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany
| | - Konrad Sandhoff
- LIMES Institute, Membrane Biology & Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany.
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Bryksa BC, Yada RY. Protein Structure Insights into the Bilayer Interactions of the Saposin-Like Domain of Solanum tuberosum Aspartic Protease. Sci Rep 2017; 7:16911. [PMID: 29208977 PMCID: PMC5717070 DOI: 10.1038/s41598-017-16734-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Accepted: 11/16/2017] [Indexed: 12/26/2022] Open
Abstract
Many plant aspartic proteases contain a saposin-like domain whose principal functions are intracellular sorting and host defence. Its structure is characterised by helical segments cross-linked by three highly conserved cystines. The present study on the saposin-like domain of Solanum tuberosum aspartic protease revealed that acidification from inactive to active conditions causes dimerisation and a strand-to-helix secondary structure transition independent of bilayer interaction. Bilayer fusion was shown to occur under reducing conditions yielding a faster shift to larger vesicle sizes relative to native conditions, implying that a lower level structural motif might be bilayer-active. Characterisation of peptide sequences based on the domain’s secondary structural regions showed helix-3 to be active (~4% of the full domain’s activity), and mutation of its sole positively charged residue resulted in loss of activity and disordering of structure. Also, the peptides’ respective circular dichroism spectra suggested that native folding within the full domain is dependent on surrounding structure. Overall, the present study reveals that the aspartic protease saposin-like domain active structure is an open saposin fold dimer whose formation is pH-dependent, and that a bilayer-active motif shared among non-saposin membrane-active proteins including certain plant defence proteins is nested within an overall structure essential for native functionality.
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Affiliation(s)
- Brian C Bryksa
- Ontario Agricultural College, University of Guelph, N1G 2W1, Guelph, Ontario, Canada
| | - Rickey Y Yada
- Faculty of Land and Food Systems, University of British Columbia, Vancouver, V6T 1Z4, British Columbia, Canada.
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Abdul-Hammed M, Breiden B, Schwarzmann G, Sandhoff K. Lipids regulate the hydrolysis of membrane bound glucosylceramide by lysosomal β-glucocerebrosidase. J Lipid Res 2017; 58:563-577. [PMID: 28126847 DOI: 10.1194/jlr.m073510] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2016] [Revised: 01/24/2017] [Indexed: 01/24/2023] Open
Abstract
Glucosylceramide (GlcCer) is the primary storage lipid in the lysosomes of Gaucher patients and a secondary one in Niemann-Pick disease types A, B, and C. The regulatory roles of lipids on the hydrolysis of membrane bound GlcCer by lysosomal β-glucocerebrosidase (GBA1) was probed using a detergent-free liposomal assay. The degradation rarely occurs at uncharged liposomal surfaces in the absence of saposin (Sap) C. However, anionic lipids stimulate GlcCer hydrolysis at low pH by up to 1,000-fold depending on the nature and position of the negative charges in their head groups while cationic lipids inhibit the degradation, thus showing the importance of electrostatic interactions between the polycationic GBA1 and the negatively charged vesicle surfaces at low pH. Ceramide, fatty acids, monoacylglycerol, and diacylglycerol also stimulate GlcCer hydrolysis while SM, sphingosine, and sphinganine play strong inhibitory roles, thereby explaining the secondary storage of GlcCer in Niemann-Pick diseases. Surprisingly, cholesterol stimulates GlcCer degradation in the presence of bis(monoacylglycero)phosphate (BMP). Sap C strongly stimulates GlcCer hydrolysis even in the absence of BMP and the regulatory roles of the intraendolysosomal lipids on its activity is discussed. Our data suggest that these strong modifiers of GlcCer hydrolysis affect the genotype-phenotype correlation in several cases of Gaucher patients independent of the types.
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Affiliation(s)
- Misbaudeen Abdul-Hammed
- Life and Medical Sciences (LIMES) Institut, Membrane Biology and Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany.,Biophysical Chemistry Group, Department of Pure and Applied Chemistry, Ladoke Akintola University of Technology, Ogbomoso, Nigeria
| | - Bernadette Breiden
- Life and Medical Sciences (LIMES) Institut, Membrane Biology and Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany
| | - Günter Schwarzmann
- Life and Medical Sciences (LIMES) Institut, Membrane Biology and Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany
| | - Konrad Sandhoff
- Life and Medical Sciences (LIMES) Institut, Membrane Biology and Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Bonn, Germany
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Davis HW, Hussain N, Qi X. Detection of cancer cells using SapC-DOPS nanovesicles. Mol Cancer 2016; 15:33. [PMID: 27160923 PMCID: PMC4862232 DOI: 10.1186/s12943-016-0519-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 05/03/2016] [Indexed: 12/15/2022] Open
Abstract
Unlike normal cells, cancer cells express high levels of phosphatidylserine on the extracellular leaflet of their cell membrane. Exploiting this characteristic, our lab developed a therapeutic agent that consists of the fusogenic protein, saposin C (SapC) which is embedded in dioleoylphosphatidylserine (DOPS) vesicles. These nanovesicles selectively target cancer cells and induce apoptosis. Here we review the data supporting use of SapC-DOPS to locate tumors for surgical resection or for treatment. In addition, there is important evidence suggesting that SapC-DOPS may also prove to be an effective novel cancer therapeutic reagent. Given that SapC-DOPS is easily labeled with lipophilic dyes, it has been combined with the far-red fluorescent dye, CellVue Maroon (CVM), for tumor targeting studies. We also have used contrast agents incorporated in the SapC-DOPS nanovesicles for computed tomography and magnetic resonance imaging, and review that data here. Administered intravenously, the fluorescently labeled SapC-DOPS traversed the blood–brain tumor barrier enabling identification of brain tumors. SapC-DOPS-CVM also detected a variety of other mouse tumors in vivo, rendering them observable by optical imaging using IVIS and multi-angle rotational optical imaging. Dye is detected within 30 min and remains within tumor for at least 7 days, whereas non-tumor tissues were unstained (some dye observed in the liver was transient, likely representing degradation products). Additionally, labeled SapC-DOPS ex vivo delineated tumors in human histological specimens. SapC-DOPS can also be labeled with contrast reagents for computed tomography or magnetic resonance imaging. In conclusion, labeled SapC-DOPS provides a convenient, specific, and nontoxic method for detecting tumors while concurrently offering a therapeutic benefit.
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Affiliation(s)
- Harold W Davis
- Division of Hematology/Oncology, Translational Medicine Laboratory, Department of Internal Medicine, University of Cincinnati College of Medicine, and Brain Tumor Center at UC Neuroscience Institute, 3512 Eden Avenue, Cincinnati, OH, 45267-0508, USA
| | - Nida Hussain
- Division of Hematology/Oncology, Translational Medicine Laboratory, Department of Internal Medicine, University of Cincinnati College of Medicine, and Brain Tumor Center at UC Neuroscience Institute, 3512 Eden Avenue, Cincinnati, OH, 45267-0508, USA
| | - Xiaoyang Qi
- Division of Hematology/Oncology, Translational Medicine Laboratory, Department of Internal Medicine, University of Cincinnati College of Medicine, and Brain Tumor Center at UC Neuroscience Institute, 3512 Eden Avenue, Cincinnati, OH, 45267-0508, USA. .,Division of Human Genetics, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
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Sandhoff K. Neuronal sphingolipidoses: Membrane lipids and sphingolipid activator proteins regulate lysosomal sphingolipid catabolism. Biochimie 2016; 130:146-151. [PMID: 27157270 DOI: 10.1016/j.biochi.2016.05.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 05/03/2016] [Indexed: 11/16/2022]
Abstract
Glycosphingolipids and sphingolipids of cellular plasma membranes (PMs) reach luminal intra-lysosomal vesicles (LVs) for degradation mainly by pathways of endocytosis. After a sorting and maturation process (e.g. degradation of sphingomyelin (SM) and secretion of cholesterol), sphingolipids of the LVs are digested by soluble enzymes with the help of activator (lipid binding and transfer) proteins. Inherited defects of lipid-cleaving enzymes and lipid binding and transfer proteins cause manifold and fatal, often neurodegenerative diseases. The review summarizes recent findings on the regulation of sphingolipid catabolism and cholesterol secretion from the endosomal compartment by lipid modifiers, an essential stimulation by anionic membrane lipids and an inhibition of crucial steps by cholesterol and SM. Reconstitution experiments in the presence of all proteins needed, hydrolase and activator proteins, reveal an up to 10-fold increase of ganglioside catabolism just by the incorporation of anionic lipids into the ganglioside carrying membranes, whereas an additional incorporation of cholesterol inhibits GM2 catabolism substantially. It is suggested that lipid and other low molecular modifiers affect the genotype-phenotype relationship observed in patients with lysosomal diseases.
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Affiliation(s)
- Konrad Sandhoff
- University of Bonn, LIMES Institute, c/o Kekulé-Institute, Gerhard-Domagk-Str. 1, 53121 Bonn, Germany.
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10
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Schwarzmann G, Breiden B, Sandhoff K. Membrane-spanning lipids for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer. J Lipid Res 2015; 56:1861-79. [PMID: 26269359 DOI: 10.1194/jlr.m056929] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Indexed: 12/17/2022] Open
Abstract
A Förster resonance energy transfer-based fusion and transfer assay was developed to study, in model membranes, protein-mediated membrane fusion and intermembrane lipid transfer of fluorescent sphingolipid analogs. For this assay, it became necessary to apply labeled reporter molecules that are resistant to spontaneous as well as protein-mediated intermembrane transfer. The novelty of this assay is the use of nonextractable fluorescent membrane-spanning bipolar lipids. Starting from the tetraether lipid caldarchaeol, we synthesized fluorescent analogs with fluorophores at both polar ends. In addition, we synthesized radioactive glycosylated caldarchaeols. These labeled lipids were shown to stretch through bilayer membranes rather than to loop within a single lipid layer of liposomes. More important, the membrane-spanning lipids (MSLs) in contrast to phosphoglycerides proved to be nonextractable by proteins. We could show that the GM2 activator protein (GM2AP) is promiscuous with respect to glycero- and sphingolipid transfer. Saposin (Sap) B also transferred sphingolipids albeit with kinetics different from GM2AP. In addition, we could unambiguously show that the recombinant activator protein Sap C x His6 induced membrane fusion rather than intermembrane lipid transfer. These findings showed that these novel MSLs, in contrast with fluorescent phosphoglycerolipids, are well suited for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer.
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Affiliation(s)
- Günter Schwarzmann
- Life & Medical Sciences (LIMES) Institute, Membrane Biology & Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, D-53121 Bonn, Germany
| | - Bernadette Breiden
- Life & Medical Sciences (LIMES) Institute, Membrane Biology & Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, D-53121 Bonn, Germany
| | - Konrad Sandhoff
- Life & Medical Sciences (LIMES) Institute, Membrane Biology & Lipid Biochemistry Unit, Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, D-53121 Bonn, Germany
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Blanco VM, Chu Z, Vallabhapurapu SD, Sulaiman MK, Kendler A, Rixe O, Warnick RE, Franco RS, Qi X. Phosphatidylserine-selective targeting and anticancer effects of SapC-DOPS nanovesicles on brain tumors. Oncotarget 2015; 5:7105-18. [PMID: 25051370 PMCID: PMC4196187 DOI: 10.18632/oncotarget.2214] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Brain tumors, either primary (e.g., glioblastoma multiforme) or secondary (metastatic), remain among the most intractable and fatal of all cancers. We have shown that nanovesicles consisting of Saposin C (SapC) and dioleylphosphatidylserine (DOPS) are able to effectively target and kill cancer cells both in vitro and in vivo. These actions are a consequence of the affinity of SapC-DOPS for phosphatidylserine, an acidic phospholipid abundantly present in the outer membrane of a variety of tumor cells and tumor-associated vasculature. In this study, we first characterize SapC-DOPS bioavailability and antitumor effects on human glioblastoma xenografts, and confirm SapC-DOPS specificity towards phosphatidylserine by showing that glioblastoma targeting is abrogated after in vivo exposure to lactadherin, which binds phosphatidylserine with high affinity. Second, we demonstrate that SapC-DOPS selectively targets brain metastases-forming cancer cells both in vitro, in co-cultures with human astrocytes, and in vivo, in mouse models of brain metastases derived from human breast or lung cancer cells. Third, we demonstrate that SapC-DOPS nanovesicles have cytotoxic activity against metastatic breast cancer cells in vitro, and prolong the survival of mice harboring brain metastases. Taken together, these results support the potential of SapC-DOPS for the diagnosis and therapy of primary and metastatic brain tumors.
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Affiliation(s)
- Víctor M Blanco
- Division of Hematology and Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Zhengtao Chu
- Division of Hematology and Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio; Division of Human Genetics, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
| | - Subrahmanya D Vallabhapurapu
- Division of Hematology and Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Mahaboob K Sulaiman
- Division of Hematology and Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Ady Kendler
- Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Olivier Rixe
- Division of Hematology/Oncology, Georgia Regents University, GRU Cancer Center, Augusta, Georgia
| | - Ronald E Warnick
- Department of Neurosurgery, University of Cincinnati Brain Tumor Center, and Mayfield Clinic, Cincinnati, Ohio
| | - Robert S Franco
- Division of Hematology and Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio
| | - Xiaoyang Qi
- Division of Hematology and Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio; Division of Human Genetics, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio
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12
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De Moura DC, Bryksa BC, Yada RY. In silico insights into protein-protein interactions and folding dynamics of the saposin-like domain of Solanum tuberosum aspartic protease. PLoS One 2014; 9:e104315. [PMID: 25188221 PMCID: PMC4154668 DOI: 10.1371/journal.pone.0104315] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2014] [Accepted: 06/09/2014] [Indexed: 12/29/2022] Open
Abstract
The plant-specific insert is an approximately 100-residue domain found exclusively within the C-terminal lobe of some plant aspartic proteases. Structurally, this domain is a member of the saposin-like protein family, and is involved in plant pathogen defense as well as vacuolar targeting of the parent protease molecule. Similar to other members of the saposin-like protein family, most notably saposins A and C, the recently resolved crystal structure of potato (Solanum tuberosum) plant-specific insert has been shown to exist in a substrate-bound open conformation in which the plant-specific insert oligomerizes to form homodimers. In addition to the open structure, a closed conformation also exists having the classic saposin fold of the saposin-like protein family as observed in the crystal structure of barley (Hordeum vulgare L.) plant-specific insert. In the present study, the mechanisms of tertiary and quaternary conformation changes of potato plant-specific insert were investigated in silico as a function of pH. Umbrella sampling and determination of the free energy change of dissociation of the plant-specific insert homodimer revealed that increasing the pH of the system to near physiological levels reduced the free energy barrier to dissociation. Furthermore, principal component analysis was used to characterize conformational changes at both acidic and neutral pH. The results indicated that the plant-specific insert may adopt a tertiary structure similar to the characteristic saposin fold and suggest a potential new structural motif among saposin-like proteins. To our knowledge, this acidified PSI structure presents the first example of an alternative saposin-fold motif for any member of the large and diverse SAPLIP family.
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Affiliation(s)
- Dref C. De Moura
- Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada
- Department of Food Science, University of Guelph, Guelph, Ontario, Canada
| | - Brian C. Bryksa
- Department of Food Science, University of Guelph, Guelph, Ontario, Canada
| | - Rickey Y. Yada
- Biophysics Interdepartmental Group, University of Guelph, Guelph, Ontario, Canada
- Department of Food Science, University of Guelph, Guelph, Ontario, Canada
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13
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Chu Z, Abu-Baker S, Palascak MB, Ahmad SA, Franco RS, Qi X. Targeting and cytotoxicity of SapC-DOPS nanovesicles in pancreatic cancer. PLoS One 2013; 8:e75507. [PMID: 24124494 PMCID: PMC3790873 DOI: 10.1371/journal.pone.0075507] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2013] [Accepted: 08/14/2013] [Indexed: 01/05/2023] Open
Abstract
Only a small number of promising drugs target pancreatic cancer, which is the fourth leading cause of cancer deaths with a 5-year survival of less than 5%. Our goal is to develop a new biotherapeutic agent in which a lysosomal protein (saposin C, SapC) and a phospholipid (dioleoylphosphatidylserine, DOPS) are assembled into nanovesicles (SapC-DOPS) for treating pancreatic cancer. A distinguishing feature of SapC-DOPS nanovesicles is their high affinity for phosphatidylserine (PS) rich microdomains, which are abnormally exposed on the membrane surface of human pancreatic tumor cells. To evaluate the role of external cell PS, in vitro assays were used to correlate PS exposure and the cytotoxic effect of SapC-DOPS in human tumor and nontumorigenic pancreatic cells. Next, pancreatic tumor xenografts (orthotopic and subcutaneous models) were used for tumor targeting and therapeutic efficacy studies with systemic SapC-DOPS treatment. We observed that the nanovesicles selectively killed human pancreatic cancer cells in vitro by inducing apoptotic death, whereas untransformed cells remained unaffected. This in vitro cytotoxic effect correlated to the surface exposure level of PS on the tumor cells. Using xenografts, animals treated with SapC-DOPS showed clear survival benefits and their tumors shrank or disappeared. Furthermore, using a double-tracking method in live mice, we showed that the nanovesicles were specifically targeted to orthotopically-implanted, bioluminescent pancreatic tumors. These data suggest that the acidic phospholipid PS is a biomarker for pancreatic cancer that can be effectively targeted for therapy utilizing cancer-selective SapC-DOPS nanovesicles. This study provides convincing evidence in support of developing a new therapeutic approach to pancreatic cancer.
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Affiliation(s)
- Zhengtao Chu
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Shadi Abu-Baker
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Mary B. Palascak
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Syed A. Ahmad
- Department of Surgery, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Robert S. Franco
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
| | - Xiaoyang Qi
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
- Division of Human Genetics, Department of Pediatrics, Cincinnati Children’s Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, Ohio, United States of America
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14
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Wojton J, Chu Z, Mathsyaraja H, Meisen WH, Denton N, Kwon CH, Chow LM, Palascak M, Franco R, Bourdeau T, Thornton S, Ostrowski MC, Kaur B, Qi X. Systemic delivery of SapC-DOPS has antiangiogenic and antitumor effects against glioblastoma. Mol Ther 2013; 21:1517-25. [PMID: 23732993 DOI: 10.1038/mt.2013.114] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 04/23/2013] [Indexed: 01/12/2023] Open
Abstract
Saposin C-dioleoylphosphatidylserine (SapC-DOPS) nanovesicles are a nanotherapeutic which effectively target and destroy cancer cells. Here, we explore the systemic use of SapC-DOPS in several models of brain cancer, including glioblastoma multiforme (GBM), and the molecular mechanism behind its tumor-selective targeting specificity. Using two validated spontaneous brain tumor models, we demonstrate the ability of SapC-DOPS to selectively and effectively cross the blood-brain tumor barrier (BBTB) to target brain tumors in vivo and reveal the targeting to be contingent on the exposure of the anionic phospholipid phosphatidylserine (PtdSer). Increased cell surface expression of PtdSer levels was found to correlate with SapC-DOPS-induced killing efficacy, and tumor targeting in vivo was inhibited by blocking PtdSer exposed on cells. Apart from cancer cell killing, SapC-DOPS also exerted a strong antiangiogenic activity in vitro and in vivo. Interestingly, unlike traditional chemotherapy, hypoxic cells were sensitized to SapC-DOPS-mediated killing. This study emphasizes the importance of PtdSer exposure for SapC-DOPS targeting and supports the further development of SapC-DOPS as a novel antitumor and antiangiogenic agent for brain tumors.
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Affiliation(s)
- Jeffrey Wojton
- Dardinger Laboratory for Neuro-oncology and Neurosciences, Department of Neurological Surgery, The Ohio State University Medical Center, Columbus, Ohio 43210, USA
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15
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Körschen HG, Yildiz Y, Raju DN, Schonauer S, Bönigk W, Jansen V, Kremmer E, Kaupp UB, Wachten D. The non-lysosomal β-glucosidase GBA2 is a non-integral membrane-associated protein at the endoplasmic reticulum (ER) and Golgi. J Biol Chem 2012; 288:3381-93. [PMID: 23250757 DOI: 10.1074/jbc.m112.414714] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
GBA1 and GBA2 are both β-glucosidases, which cleave glucosylceramide (GlcCer) to glucose and ceramide. GlcCer is a main precursor for higher order glycosphingolipids but might also serve as intracellular messenger. Mutations in the lysosomal GBA1 underlie Gaucher disease, the most common lysosomal storage disease in humans. Knocking out the non-lysosomal GBA2 in mice results in accumulation of GlcCer outside the lysosomes in various tissues (e.g. testis and liver) and impairs sperm development and liver regeneration. However, the underlying mechanisms are not well understood. To reveal the physiological function of GBA2 and, thereby, of the non-lysosomal GlcCer pool, it is important to characterize the localization of GBA2 and its activity in different tissues. Thus, we generated GBA2-specific antibodies and developed an assay that discriminates between GBA1 and GBA2 without the use of detergent. We show that GBA2 is not, as previously thought, an integral membrane protein but rather a cytosolic protein that tightly associates with cellular membranes. The interaction with the membrane, in particular with phospholipids, is important for its activity. GBA2 is localized at the ER and Golgi, which puts GBA2 in a key position for a lysosome-independent route of GlcCer-dependent signaling. Furthermore, our results suggest that GBA2 might affect the phenotype of Gaucher disease, because GBA2 activity is reduced in Gba1 knock-out fibroblasts and fibroblasts from a Gaucher patient. Our results provide the basis to understand the mechanism for GBA2 function in vivo and might help to unravel the role of GBA2 during pathogenesis of Gaucher disease.
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Affiliation(s)
- Heinz G Körschen
- Department of Molecular Sensory Systems, Center of Advanced European Studies and Research, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany
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16
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Tamargo RJ, Velayati A, Goldin E, Sidransky E. The role of saposin C in Gaucher disease. Mol Genet Metab 2012; 106:257-63. [PMID: 22652185 PMCID: PMC3534739 DOI: 10.1016/j.ymgme.2012.04.024] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/12/2012] [Revised: 04/28/2012] [Accepted: 04/29/2012] [Indexed: 12/16/2022]
Abstract
Saposin C is one of four homologous proteins derived from sequential cleavage of the saposin precursor protein, prosaposin. It is an essential activator for glucocerebrosidase, the enzyme deficient in Gaucher disease. Gaucher disease is a rare autosomal recessive lysosomal storage disorder caused by mutations in the GBA gene that exhibits vast phenotypic heterogeneity, despite its designation as a "simple" Mendelian disorder. The observed phenotypic variability has led to a search for disease modifiers that can alter the Gaucher phenotype. The PSAP gene encoding saposin C is a prime candidate modifier for Gaucher disease. In humans, saposin C deficiency due to mutations in PSAP results in a Gaucher-like phenotype, despite normal in vitro glucocerebrosidase activity. Saposin C deficiency has also been shown to modify phenotype in one mouse model of Gaucher disease. The role of saposin C as an activator required for normal glucocerebrosidase function, and the consequences of saposin C deficiency are described, and are being explored as potential modifying factors in patients with Gaucher disease.
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Affiliation(s)
| | | | | | - Ellen Sidransky
- Corresponding author at: Section on Molecular Neurogenetics, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Building 35, Room 1A-213, 35 Convent Dr., MSC 3708, Bethesda, MD 20892-3708, USA. Fax: +1 301 402 6438
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17
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Abu-Baker S, Chu Z, Stevens AM, Li J, Qi X. Cytotoxicity and Selectivity in Skin Cancer by SapC-DOPS Nanovesicles. ACTA ACUST UNITED AC 2012; 3:321-326. [PMID: 25485166 DOI: 10.4236/jct.2012.34041] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Squamous cell carcinoma (SCC) and melanoma are malignant human cancers of the skin with an annual mortality that exceed 10,000 cases every year in the USA alone. In this study, the lysosomal protein saposin C (SapC) and the phospholipid dioloylphosphatidylserine (DOPS) were assembled into cancer-selective nanovesicles (SapC-DOPS) and successfully tested using several in vitro and in vivo skin cancer models. Using MTT assay that measures the percentage of cell death, SapC-DOPS cytotoxic effect on three skin tumor cell lines (squamous cell carcinoma, SK-MEL-28, and MeWo) was compared to two normal nontumorigenic skin cells lines, normal immortalized keratinocyte (NIK) and human fibroblast cell (HFC). We observed that the nanovesicles selectively killed the skin cancer cells by inducing apoptotic cell death whereas untransformed skin cancer cells remained unaffected. Using subcutaneous skin tumor xenografts, animals treated with SapC-DOPS by subcutaneous injection showed a 79.4 % tumor reduced compared to the control after 4 days of treatment. We observed that the nanovesicles killed skin cancer cells by inducing apoptotic cell death compared to the control as revealed by TUNEL staining of xenograft tumor sections.
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Affiliation(s)
- Shadi Abu-Baker
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH
| | - Zhengtao Chu
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH ; Division of Human Genetics, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH
| | - Ashley M Stevens
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH ; Division of Human Genetics, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH
| | - Jie Li
- Department of Dermatology, University of Miami, Miami, FL
| | - Xiaoyang Qi
- Division of Hematology/Oncology, Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, OH ; Division of Human Genetics, Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH
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18
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Bryksa BC, Bhaumik P, Magracheva E, De Moura DC, Kurylowicz M, Zdanov A, Dutcher JR, Wlodawer A, Yada RY. Structure and mechanism of the saposin-like domain of a plant aspartic protease. J Biol Chem 2011; 286:28265-75. [PMID: 21676875 DOI: 10.1074/jbc.m111.252619] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Many plant aspartic proteases contain an additional sequence of ~100 amino acids termed the plant-specific insert, which is involved in host defense and vacuolar targeting. Similar to all saposin-like proteins, the plant-specific insert functions via protein-membrane interactions; however, the structural basis for such interactions has not been studied, and the nature of plant-specific insert-mediated membrane disruption has not been characterized. In the present study, the crystal structure of the saposin-like domain of potato aspartic protease was resolved at a resolution of 1.9 Å, revealing an open V-shaped configuration similar to the open structure of human saposin C. Notably, vesicle disruption activity followed Michaelis-Menten-like kinetics, a finding not previously reported for saposin-like proteins including plant-specific inserts. Circular dichroism data suggested that secondary structure was pH-dependent in a fashion similar to influenza A hemagglutinin fusion peptide. Membrane effects characterized by atomic force microscopy and light scattering indicated bilayer solubilization as well as fusogenic activity. Taken together, the present study is the first report to elucidate the membrane interaction mechanism of plant saposin-like domains whereby pH-dependent membrane interactions resulted in bilayer fusogenic activity that probably arose from a viral type pH-dependent helix-kink-helix motif at the plant-specific insert N terminus.
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Affiliation(s)
- Brian C Bryksa
- Department of Food Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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19
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Yoneshige A, Suzuki K, Suzuki K, Matsuda J. A mutation in the saposin C domain of the sphingolipid activator protein (Prosaposin) gene causes neurodegenerative disease in mice. J Neurosci Res 2010; 88:2118-34. [PMID: 20175216 DOI: 10.1002/jnr.22371] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Saposins A, B, C, and D are small amphiphatic glycoproteins that are encoded in tandem within a precursor protein (prosaposin, PSAP), and are required for in vivo degradation of sphingolipids. Humans with saposin C deficiency exhibit the clinical presentation of Gaucher-like disease. We generated two types of saposin C mutant mice, one carrying a homozygous missense mutation (C384S) in the saposin C domain of prosaposin (Sap-C(-/-)) and the other carrying the compound heterozygous mutation with a second null Psap allele (Psap(-/C384S)). During early life stages, both Sap-C(-/-) and Psap(-/C384S) mice grew normally; however, they developed progressive motor and behavioral deficits after 3 months of age and the majority of affected mice could scarcely move by about 15 months. They showed no signs of hepatosplenomegaly throughout their lives. No accumulation of glucosylceramide and glucosylsphingosine was detected in the brain or liver of both Sap-C(-/-) and Psap(-/C384S) mice. Neuropathological analyses revealed patterned loss of cerebellar Purkinje cells, widespread axonal spheroids filled with membrane-derived concentric or lamellar electron-dense bodies, and lipofuscin-like deposition in the neurons. Soap-bubble-like inclusion bodies were detected in the trigeminal ganglion cells and the vascular endothelial cells. Compound heterozygous Psap(-/C384S) mice showed qualitatively identical but faster progression of the neurological phenotypes than Sap-C(-/-) mice. These results suggest the in vivo role of saposin C in axonal membrane homeostasis, the disruption of which leads to neurodegeneration in lysosomal storage disease.
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Affiliation(s)
- Azusa Yoneshige
- Institute of Glycoscience, Tokai University, Hiratsuka, Kanagawa, Japan
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20
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Lu K, Zhao G, Lu H, Zhao S, Song Y, Qi X, Hou Y. Toll-like receptor 4 can recognize SapC-DOPS to stimulate macrophages to express several cytokines. Inflamm Res 2010; 60:153-61. [PMID: 20853174 DOI: 10.1007/s00011-010-0249-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2010] [Revised: 07/20/2010] [Accepted: 09/06/2010] [Indexed: 02/04/2023] Open
Abstract
OBJECTIVE AND DESIGN SapC-DOPS is a newly combined compound consisting of saposin C and dioleoylphosphatidylserine (DOPS). Our recent study showed that SapC-DOPS exhibits anti-tumor activity. However, SapC-DOPS has recognition elements of Toll-like receptor (TLR) 2 and TLR4; therefore, we want to know whether SapC-DOPS can induce abnormal immunoreaction via identification TLRs. METHODS We investigated the capacity of SapC-DOPS to induce cytokines in vivo and in vitro and analyzed the involvement of TLR and NF-kB in these cytokines production. RESULTS SapC-DOPS could activate the cytokine production by peripheral macrophages, enhance the expressions of TLR4 and stimulate the NF-κB nuclear translocation. PDTC, an NF-κB inhibitor, could decrease the SapC-DOPS inducible TNF-α and IL-1β production. CONCLUSIONS SapC-DOPS was similar to LPS in the immune response and may induce the production of cytokines in macrophages via the TLR4 signaling pathway and, at least in part, the alteration of the NF-κB pathway.
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Affiliation(s)
- Kaihua Lu
- Immunology and Reproductive Biology Lab of Medical School and State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, People's Republic of China
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21
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Abdul-Hammed M, Breiden B, Adebayo MA, Babalola JO, Schwarzmann G, Sandhoff K. Role of endosomal membrane lipids and NPC2 in cholesterol transfer and membrane fusion. J Lipid Res 2010; 51:1747-60. [PMID: 20179319 PMCID: PMC2882726 DOI: 10.1194/jlr.m003822] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
We examined the effect of Niemann-Pick disease type 2 (NPC2) protein and some late endosomal lipids [sphingomyelin, ceramide and bis(monoacylglycero)phosphate (BMP)] on cholesterol transfer and membrane fusion. Of all lipid-binding proteins tested, only NPC2 transferred cholesterol at a substantial rate, with no transfer of ceramide, GM3, galactosylceramide, sulfatide, phosphatidylethanolamine, or phosphatidylserine. Cholesterol transfer was greatly stimulated by BMP, little by ceramide, and strongly inhibited by sphingomyelin. Cholesterol and ceramide were also significantly transferred in the absence of protein. This spontaneous transfer of cholesterol was greatly enhanced by ceramide, slightly by BMP, and strongly inhibited by sphingomyelin. In our transfer assay, biotinylated donor liposomes were separated from fluorescent acceptor liposomes by streptavidin-coated magnetic beads. Thus, the loss of fluorescence indicated membrane fusion. Ceramide induced spontaneous fusion of lipid vesicles even at very low concentrations, while BMP and sphingomyelin did so at about 20 mol% and 10 mol% concentrations, respectively. In addition to transfer of cholesterol, NPC2 induced membrane fusion, although less than saposin-C. In this process, BMP and ceramide had a strong and mild stimulating effect, and sphingomyelin an inhibiting effect, respectively. Note that the effects of the lipids on cholesterol transfer mediated by NPC2 were similar to their effect on membrane fusion induced by NPC2 and saposin-C.
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Affiliation(s)
- Misbaudeen Abdul-Hammed
- Membrane Biology and Biochemistry Unit, Life and Medical Sciences Institute (LIMES), Bonn, Germany
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22
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Abstract
Saposins or sphingolipid activator proteins (SAPs) are small, nonenzymatic glycoproteins that are ubiquitously present in lysosomes. SAPs comprise the five molecules saposins A-D and the GM2 activator protein. Saposins are essential for sphingolipid degradation and membrane digestion. On the one hand, they bind the respective hydrolases required to catabolize sphingolipid molecules; on the other hand, saposins can interact with intralysosomal membrane structures to render lipids accessible to their degrading enzymes. Thus, saposins bridge the physicochemical gap between lipid substrate and hydrophilic hydrolases. Accordingly, defects in saposin function can lead to lysosomal lipid accumulation. In addition to their specific functions in sphingolipid metabolism, saposins have membrane-perturbing properties. At the low pH of lysosomes, saposins get protonated and exhibit a high binding affinity for anionic phospholipids. Based on their universal principle to interact with membrane bilayers, we present the immunological functions of saposins with regard to lipid antigen presentation to CD1-restricted T cells, processing of apoptotic bodies for antigen delivery and cross-priming, as well as their potential antimicrobial impact.
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Affiliation(s)
- Alexandre Darmoise
- Program in Cellular and Molecular Medicine at Children's Hospital, Immune Disease Institute, Department of Pathology, Harvard Medical School, Boston, MA, USA
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23
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Qi X, Chu Z, Mahller YY, Stringer KF, Witte DP, Cripe TP. Cancer-selective targeting and cytotoxicity by liposomal-coupled lysosomal saposin C protein. Clin Cancer Res 2009; 15:5840-51. [PMID: 19737950 DOI: 10.1158/1078-0432.ccr-08-3285] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
PURPOSE Saposin C is a multifunctional protein known to activate lysosomal enzymes and induce membrane fusion in an acidic environment. Excessive accumulation of lipid-coupled saposin C in lysosomes is cytotoxic. Because neoplasms generate an acidic microenvironment, caused by leakage of lysosomal enzymes and hypoxia, we hypothesized that saposin C may be an effective anticancer agent. We investigated the antitumor efficacy and systemic biodistribution of nanovesicles comprised of saposin C coupled with dioleoylphosphatidylserine in preclinical cancer models. EXPERIMENTAL DESIGN Neuroblastoma, malignant peripheral nerve sheath tumor and, breast cancer cells were treated with saposin C-dioleoylphosphatidylserine nanovesicles and assessed for cell viability, ceramide elevation, caspase activation, and apoptosis. Fluorescently labeled saposin C-dioleoylphosphatidylserine was i.v. injected to determine in vivo tumor-targeting specificity. Antitumor activity and toxicity profile of saposin C-dioleoylphosphatidylserine were evaluated in xenograft models. RESULTS Saposin C-dioleoylphosphatidylserine nanovesicles, with a mean diameter of approximately 190 nm, showed specific tumor-targeting activity shown through in vivo imaging. Following i.v. administration, saposin C-dioleoylphosphatidylserine nanovesicles preferentially accumulated in tumor vessels and cells in tumor-bearing mice. Saposin C-dioleoylphosphatidylserine induced apoptosis in multiple cancer cell types while sparing normal cells and tissues. The mechanism of saposin C-dioleoylphosphatidylserine induction of apoptosis was determined to be in part through elevation of intracellular ceramides, followed by caspase activation. In in vivo models, saposin C-dioleoylphosphatidylserine nanovesicles significantly inhibited growth of preclinical xenografts of neuroblastoma and malignant peripheral nerve sheath tumor. I.v. dosing of saposin C-dioleoylphosphatidylserine showed no toxic effects in nontumor tissues. CONCLUSIONS Saposin C-dioleoylphosphatidylserine nanovesicles offer promise as a novel, nontoxic, cancer-targeted, antitumor agent for treating a broad range of cancers.
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Affiliation(s)
- Xiaoyang Qi
- Division and Program in HumanGenetics, 3333 Burnet Avenue, Cincinnati, Ohio 45229-3039, USA.
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24
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CHU ZHENGTAO, SUN YING, KUAN CHIAYI, GRABOWSKI GREGORYA, QI XIAOYANG. Saposin C: Neuronal Effect and CNS Delivery by Liposomes. Ann N Y Acad Sci 2008. [DOI: 10.1111/j.1749-6632.2005.tb00031.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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25
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Rossmann M, Schultz-Heienbrok R, Behlke J, Remmel N, Alings C, Sandhoff K, Saenger W, Maier T. Crystal Structures of Human Saposins C and D: Implications for Lipid Recognition and Membrane Interactions. Structure 2008; 16:809-17. [DOI: 10.1016/j.str.2008.02.016] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2007] [Revised: 01/30/2008] [Accepted: 02/06/2008] [Indexed: 01/18/2023]
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26
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Atrian S, López-Viñas E, Gómez-Puertas P, Chabás A, Vilageliu L, Grinberg D. An evolutionary and structure-based docking model for glucocerebrosidase-saposin C and glucocerebrosidase-substrate interactions - relevance for Gaucher disease. Proteins 2008; 70:882-91. [PMID: 17803231 DOI: 10.1002/prot.21554] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Gaucher disease, the most prevalent lysosomal storage disorder, is principally caused by malfunction of the lysosomal enzyme glucocerebrosidase (GBA), a 497-amino acid membrane glycoprotein that catalyzes the hydrolysis of glucosylceramide to ceramide and glucose in the presence of an essential 84-residue activator peptide named saposin C (SapC). Knowledge of the GBA structure, a typical (beta/alpha)(8) TIM barrel, explains the effect of few mutations, directly affecting or located near the catalytic site. To identify new regions crucial for proper GBA functionality, we analyzed the interactions of the enzyme with a second (substrate) and a third (cofactor) partner. We build 3D docking models of the GBA-SapC and the GBA-ceramide interactions, by means of methodologies that integrate both evolutive and structural information. The GBA-SapC docking model confirm the implication of three spatially closed regions of the GBA surface (TIM barrel-helix 6 and helix 7, and the Ig-like domain) in binding the SapC molecule. This model provides new basis to understand the pathogenicity of several mutations, such as the prevalent Leu444Pro, and the additive effect of Glu326Lys in the double mutant Glu326Lys-Leu444Pro. Overall, 39 positions in which amino acid changes are known to cause Gaucher disease were localized in the GBA regions identified in this work. Our model is discussed in relation to the phenotype (pathogenic effect) of these mutations, as well as to the enzymatic activity of the recombinant proteins when available. Both data fully correlates with the proposed model, which will provide a new tool to better understand Gaucher disease and to design new therapy strategies.
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Affiliation(s)
- Sílvia Atrian
- Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, 08028 Barcelona, Spain.
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27
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Abu-Baker S, Qi X, Lorigan GA. Investigating the interaction of saposin C with POPS and POPC phospholipids: a solid-state NMR spectroscopic study. Biophys J 2007; 93:3480-90. [PMID: 17704143 PMCID: PMC2072076 DOI: 10.1529/biophysj.107.107789] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The interaction of Saposin C (Sap C) with negatively charged phospholipids such as phosphatidylserine (PS) is essential for its biological function. In this study, Sap C (initially protonated in a weak acid) was inserted into multilamellar vesicles (MLVs) consisting of either 1-palmitoyl-2-oleoyl-sn-glycero-3-[phospho-L-serine] (negatively charged, POPS) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (neutrally charged, POPC). The MLVs were then investigated using solid-state NMR spectroscopy under neutral pH (7.0) conditions. The (2)H and (31)P solid-state NMR spectroscopic data of Sap C-POPS and Sap C-POPC MLVs (prepared under the same conditions) were compared using the (2)H order parameter profiles of the POPC-d(31) or POPS-d(31) acyl chains as well as the (31)P chemical shift anisotropy width and (31)P T(1) relaxation times of the phospholipids headgroups. All those solid-state NMR spectroscopic approaches indicate that protonated Sap C disturbs the POPS bilayers and not the POPC lipid bilayers. These observations suggest for the first time that protonated Sap C inserts into PS bilayers and forms a stable complex with the lipids even after resuspension under neutral buffer conditions. Additionally, (31)P solid-state NMR spectroscopic studies of mechanically oriented phospholipids on glass plates were conducted and perturbation effect of Sap C on both POPS and POPC bilayers was compared. Unlike POPC bilayers, the data indicates that protonated Sap C (initially protonated in a weak acid) was unable to produce well-oriented POPS bilayers on glass plates at neutral pH. Conversely, unprotonated Sap C (initially dissolved in a neutral buffer) did not interact significantly with POPS phospholipids allowing them to produce well-oriented bilayers at neutral pH.
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Affiliation(s)
- Shadi Abu-Baker
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio, USA
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28
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John M, Wendeler M, Heller M, Sandhoff K, Kessler H. Characterization of human saposins by NMR spectroscopy. Biochemistry 2006; 45:5206-16. [PMID: 16618109 DOI: 10.1021/bi051944+] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Saposins are lipid-binding and membrane-perturbing glycoproteins of the mammalian lysosomes involved in sphingolipid and membrane digestion. Although the four human saposins (Saps), A-D, are sequence-related, they are responsible for the activation of different steps in the cascade of lysosomal glycosphingolipid degradation. Saposin activity is maximal under acidic conditions, and the pH dependence of lipid and membrane binding has been assigned to conformational variability. We have employed solution NMR spectroscopy to all four (15)N-labeled human saposins at both neutral and acidic pH. Using backbone NOEs and residual dipolar couplings, the "saposin fold" comprising five alpha-helices was confirmed for Sap-A, Sap-C, and Sap-D. Structural variations within these proteins are in the order of variations between the known structures of Sap-C and NK-lysin. In contrast, Sap-B yielded spectra of very poor quality, presumably due to conformational heterogeneity and molecular association. Sap-D exists in a slow dynamic equilibrium of two conformational states with yet unknown function. At pH 4.0, where all saposins are highly unstable, Sap-C undergoes a transition to a specific dimeric state, which is likely to resemble the structure recently found in both Sap-C in a detergent environment and crystals of Sap-B.
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Affiliation(s)
- Michael John
- Department Chemie, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany
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Winkelmann J, Leippe M, Bruhn H. A novel saposin-like protein of Entamoeba histolytica with membrane-fusogenic activity. Mol Biochem Parasitol 2006; 147:85-94. [PMID: 16529828 DOI: 10.1016/j.molbiopara.2006.01.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2005] [Revised: 01/20/2006] [Accepted: 01/24/2006] [Indexed: 02/04/2023]
Abstract
Amoebapores, the pore-forming proteins of Entamoeba histolytica, are major pathogenicity factors of the parasite. Upon a comprehensive survey in the recently completed genome data sets for the protozoon, we identified in addition to the three amoebapore genes, 16 genes which are constitutively expressed and code for structurally similar proteins, all belonging to the family of saposin-like proteins. Here, we recombinantly expressed in bacteria a defined single entity of this expansive amoebic protein family, namely SAPLIP 3. The protein consists of the saposin-like domain only, comparable to amoebapores, and we characterized its interactions with membranes using different assays. In contrast to amoebapores, SAPLIP 3 neither forms pores in liposomes nor permeabilizes bacterial membranes. However, SAPLIP 3 induces leaky fusion of lipid vesicles as evidenced by fluorescence microscopic analysis and by using a fusion assay that monitors the dequenching of a lipophilic dye. The membrane-fusogenic activity of SAPLIP 3 which is dependent on the presence of negatively charged lipids and on acidic pH resembles in combination with the negative surface charge of the protein characteristics of human saposin C. Beside its function as a cofactor of sphingolipid hydrolysing enzymes, the human protein is considered to be involved in the reorganization of lysosomal compartments due to its fusogenic activity. We hypothesize that in the amoeba, SAPLIP 3 fulfils a similar function in the multifarious endo- and exocytotic transport processes.
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Affiliation(s)
- Julia Winkelmann
- Research Center for Infectious Diseases, University of Wuerzburg, Roentgenring 11, D-97070 Wuerzburg, Germany
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Liu A, Wenzel N, Qi X. Role of lysine residues in membrane anchoring of saposin C. Arch Biochem Biophys 2006; 443:101-12. [PMID: 16256068 DOI: 10.1016/j.abb.2005.09.007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2005] [Revised: 09/02/2005] [Accepted: 09/03/2005] [Indexed: 02/04/2023]
Abstract
Molecular dynamics (MD) simulations of the N-terminal region of saposin C, containing amino acid residues 4-20 (saposin C4-20), were performed over 2.5 ns in 1,2-dioleoyl-sn-glycero-3-phosphoserine (DOPS) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) monolayers. The simulations revealed several strong specific interactions of lysine 13 (Lys13) and lysine 17 (Lys17) in saposin C4-20 with the anionic phospholipids, which are required for membrane anchoring of the peptide. Membrane anchoring of saposin C4-20 facilitates saposin C-induced liposomal membrane fusion. Substitutions of Lys13 or Lys17 with alanine or glutamic acid led to a substantial loss of saposin C's fusogenicity. However, arginine replacement of Lys13 or Lys17 caused a partial loss of saposin C's fusogenic activity. The membrane anchoring of saposin C was altered in the presence of 0.4 M sodium chloride. Differential salt effects on Lys-mutant saposin Cs were observed using Trp fluorescence analysis. Low salt concentration had a more significant impact on Lys-mutant saposin C with a negatively charged amino acid residue replacement than those mutants with a positively charged or neutral residue replacement. These results indicate that positively charged amino acids at positions 13 and 17 are required for the fusogenic function of saposin C. In addition, the side-chain structure of lysine is crucial to the precise membrane anchoring which is necessary for the total fusion activity of saposin C. The MD simulations and vesicle size measurements of lysine-mutant saposins confirm the importance of the two lysine residues in saposin C4-20 for saposin C-induced fusion of negatively charged phospholipid membranes.
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Affiliation(s)
- Anping Liu
- Department of Chemistry, University of Cincinnati, P.O. Box 210172, Cincinnati, OH 45221-0172, USA
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Abu-Baker S, Qi X, Newstadt J, Lorigan GA. Structural changes in a binary mixed phospholipid bilayer of DOPG and DOPS upon saposin C interaction at acidic pH utilizing 31P and 2H solid-state NMR spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1717:58-66. [PMID: 16289479 DOI: 10.1016/j.bbamem.2005.09.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2005] [Revised: 09/07/2005] [Accepted: 09/12/2005] [Indexed: 12/15/2022]
Abstract
Saposin C (Sap C) is known to stimulate the catalytic activity of the lysosomal enzyme glucosylceramidase (GCase) that facilitates the hydrolysis of glucosylceramide to ceramide and glucose. Both Sap C and acidic phospholipids are required for full activity of GCase. In order to better understand this interaction, mixed bilayer samples prepared from dioleoylphosphatidylglycerol (DOPG) and dioleoylphosphatidylserine (DOPS) (5:3 ratio) and Sap C were investigated using (2)H and (31)P solid-state NMR spectroscopy at temperatures ranging from 25 to 50 degrees C at pH 4.7. The Sap C concentrations used to carry out these experiments were 0 mol%, 1 mol% and 3 mol% with respect to the phospholipids. The molecular order parameters (S(CD)) were calculated from the dePaked (2)H solid-state NMR spectra of Distearoyl-d70-phosphatidylglycerol (DSPG-d70) incorporated with DOPG and DOPS binary mixed bilayers. The S(CD) profiles indicate that the addition of Sap C to the negatively charged phospholipids is concentration dependent. S(CD) profiles of 1 mol% of the Sap C protein show only a very slight decrease in the acyl chain order. However, the S(CD) profiles of the 3 mol% of Sap C protein indicate that the interaction is predominantly increasing the disorder in the first half of the acyl chain near the head group (C1-C8) indicating that the amino and the carboxyl termini of Sap C are not inserting deep into the DOPG and DOPS mixed bilayers. The (31)P solid-state NMR spectra show that the chemical shift anisotropy (CSA) for both phospholipids decrease and the spectral broadening increases upon addition of Sap C to the mixed bilayers. The data indicate that Sap C interacts similarly with the head groups of both acidic phospholipids and that Sap C has no preference to DOPS over DOPG. Moreover, our solid-state NMR spectroscopic data agree with the structural model previously proposed in the literature [X. Qi, G.A. Grabowski, Differential membrane interactions of saposins A and C. Implication for the functional specificity, J. Biol. Chem. 276 (2001) 27010-27017] [1].
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Affiliation(s)
- Shadi Abu-Baker
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
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Hawkins CA, de Alba E, Tjandra N. Solution structure of human saposin C in a detergent environment. J Mol Biol 2005; 346:1381-92. [PMID: 15713488 DOI: 10.1016/j.jmb.2004.12.045] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2004] [Revised: 11/04/2004] [Accepted: 12/20/2004] [Indexed: 01/19/2023]
Abstract
Saposin C is a lysosomal, membrane-binding protein that acts as an activator for the hydrolysis of glucosylceramide by the enzyme glucocerebrosidase. We used high-resolution NMR to determine the three-dimensional solution structure of saposin C in the presence of the detergent sodium dodecyl sulfate (SDS). This structure provides the first representation of membrane bound saposin C at the atomic level. In the presence of SDS, the protein adopts an open conformation with an exposed hydrophobic pocket. In contrast, the previously reported NMR structure of saposin C in the absence of SDS is compact and contains a hydrophobic core that is not exposed to the solvent. NMR data indicate that the SDS molecules interact with the hydrophobic pocket. The structure of saposin C in the presence of SDS is very similar to a monomer in the saposin B homodimer structure. Their comparison reveals possible similarity in the type of protein/lipid interaction as well as structural components differentiating their quaternary structures and functional specificity.
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Affiliation(s)
- Cheryl A Hawkins
- Laboratory of Biophysical Chemistry, National Heart, Lung, and Blood Institute, National Institutes of Health, 50 Center Drive, Bethesda, MD 20892, USA
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Qi X, Chu Z. Fusogenic domain and lysines in saposin C. Arch Biochem Biophys 2004; 424:210-8. [PMID: 15047193 DOI: 10.1016/j.abb.2004.02.023] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2003] [Revised: 02/17/2004] [Indexed: 02/07/2023]
Abstract
Saposin C, a sphingolipid activator protein with fusogenic activity, interacts specifically with the membrane containing negatively charged, unsaturated phospholipids. The kinetics and mechanism of saposin C-induced membrane fusion were previously investigated using acidic phospholipid liposomes. A hypothetic clip-on model for such a fusion process was illustrated by the ionic binding between saposin C and lipids, as well as the inter-saposin C hydrophobic interaction. Here, we report the location of the fusogenic domain in a linear sequence at the amino-terminal half of saposin C. This domain consisted of the first and second helical sequences. Selected positively charged lysines in the fusogenic domain were mutated to study the roles of basic residues in the saposin C-induced vesicle fusion. Based on the results, Lys13 and Lys17 were critical for the fusogenic activity, but had no effect on the enzymatic activation of acid beta-glucosidase (GCase). These results clearly indicate the segregation of the fusion and activation function into two different regions of saposin C. Interestingly, all the Lys mutant saposin Cs anchored on the acidic phospholipid membrane. Our data suggest that saposin C's fusogenic and activation functions have different requirements for the orientation and insertion manners of helical peptides in membranes.
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Affiliation(s)
- Xiaoyang Qi
- The Division and Program in Human Genetics, Cincinnati Children's Hospital Research Foundation, and Department of Pediatrics, The University of Cincinnati College of Medicine, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, USA.
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Abstract
Saposin C is a small Trp-free, multifunctional glycoprotein that enhances the hydrolytic activity of acid beta-glucosidase in lysosomes. Saposin C's functions have been shown to include neuritogenic/neuroprotection effects and membrane fusion induction. Here, the mechanism and kinetics of saposin C's fusogenic activity were evaluated by fluorescence spectroscopic methods including dequenching, fluorescence resonance energy transfer, and stopped-flow analyses. Trp or dansyl groups were introduced as fluorescence reporters into selected sites of saposin C to serve as topological probes for protein-protein and protein-membrane interactions. Saposin C induction of liposomal vesicle enlargement was dependent upon anionic phospholipids and acidic pH. The initial fusion burst was completed in the timeframe of a few seconds to minutes and was dependent upon the unsaturated anionic phospholipid content. Two events were associated with saposin C-membrane interaction: membrane insertion of the saposin C terminal helices and reorientation of its central helical region. The latter conformational change likely exposed a binding site for saposins anchored on vesicles. Addition of selected saposin C peptides prior to intact saposin C in reaction mixtures abolished the liposomal fusion. These results indicated that saposin-membrane and saposin-saposin interactions are needed for the fusion process.
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Affiliation(s)
- Ying Wang
- Division and Program in Human Genetics, Children's Hospital Research Foundation, 3333 Burnet Avenue, Cincinnati, OH 45229-3039, USA
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35
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You HX, Qi X, Grabowski GA, Yu L. Phospholipid membrane interactions of saposin C: in situ atomic force microscopic study. Biophys J 2003; 84:2043-57. [PMID: 12609906 PMCID: PMC1302773 DOI: 10.1016/s0006-3495(03)75012-7] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2002] [Accepted: 10/28/2002] [Indexed: 10/21/2022] Open
Abstract
Saposin C (Sap C) is a small glycoprotein required for hydrolysis of glucosylceramidase in lysosomes. The full activity of glucosylceramidase requires the presence of both Sap C and acidic phospholipids. Interaction between Sap C and acidic phospholipid-containing membranes, a crucial step for enzyme activation, is not fully understood. In this study, the dynamic process of Sap C interaction with acidic phospholipid-containing membranes was investigated in aqueous buffer using atomic force microscopy. Sap C induced two types of membrane restructuring: formation of patch-like structural domains and the occurrence of membrane destabilization. The former caused thickness increase whereas the latter caused thickness reduction in the gel-phase membrane bilayer, possibly as a result of lipid loss or an interdigitating process. Patch-like domain formation was independent of acidic phospholipids, whereas membrane destabilization is dependent on the presence and concentration of acidic phospholipids. Sap C effects on membrane restructuring were further studied using synthetic peptides. Synthetic peptides corresponding to the amphipathic alpha-helical domains 1 (designated "H1 peptide") and 2 (H2 peptide) of Sap C were used. Our results indicated that H2 contributed to domain formation but not to membrane destabilization, whereas H1 induced neither type of membrane restructuring. However, H1 was able to mimic Sap C's destabilization effect in conjunction with H2, but only when H1 was present first and H2 was added afterwards. This study provides an approach to investigate the structure-function aspects of Sap C interaction with phospholipid membranes, with insights into the mechanism(s) of Sap C-membrane interaction.
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Affiliation(s)
- Hong Xing You
- Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, Ohio 45267-0521, USA.
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Ciaffoni F, Salvioli R, Tatti M, Arancia G, Crateri P, Vaccaro AM. Saposin D solubilizes anionic phospholipid-containing membranes. J Biol Chem 2001; 276:31583-9. [PMID: 11406625 DOI: 10.1074/jbc.m102736200] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Saposin (Sap) D is a late endosomal/lysosomal small protein, generated together with three other similar proteins, Sap A, B, and C, from the common precursor, prosaposin. Although the functions of saposins such as Sap B and C are well known (Sap B promotes the hydrolysis of sulfatides and Sap C that of glucosylceramide), neither the physiological function nor the mechanism of action of Sap D are yet fully understood. We previously found that a dramatic increase of Sap D superficial hydrophobicity, occurring at the low pH values characteristic of the late endosomal/lysosomal environment, triggers the interaction of the saposin with anionic phospholipid-containing vesicles. We have presently found that, upon lipid binding, Sap D solubilizes the membranes, as shown by the clearance of the vesicles turbidity. The results of gel filtration, density gradient centrifugation, and negative staining electron microscopy demonstrate that this effect is due to the transformation of large vesicles to smaller particles. The solubilizing effect of Sap D is highly dependent on pH, the lipid/saposin ratio, and the presence of anionic phospholipids; small variations in each of these conditions markedly influences the activity of Sap D. The present study documents the interaction of Sap D with membranes as a complex process. Anionic phospholipids attract Sap D from the medium; when the concentration of the saposin on the lipid surface reaches a critical value, the membrane breaks down into recombinant small particles enriched in anionic phospholipids. Our results suggest that the role played by Sap D is more general than promoting sphingolipid degradation, e.g. the saposin might also be a key mediator of the solubilization of intralysosomal/late endosomal anionic phospholipid-containing membranes.
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Affiliation(s)
- F Ciaffoni
- Department of Metabolism and Pathological Biochemistry, Istituto Superiore Sanita', Viale Regina Elena 299, 00161 Rome, Italy
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You HX, Yu L, Qi X. Phospholipid membrane restructuring induced by saposin C: a topographic study using atomic force microscopy. FEBS Lett 2001; 503:97-102. [PMID: 11513862 DOI: 10.1016/s0014-5793(01)02700-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The enzymatic activity of glucosylceramidase depends on the presence of saposin C (Sap C) and acidic phospholipid-containing membranes. In order to delineate the mechanism underlying Sap C stimulation of the enzyme activity, it is important to understand how Sap C interacts with phospholipid membranes. We studied the dynamic process of Sap C interaction with planar phospholipid membranes, in real time, using atomic force microscopy (AFM). The phospholipid membrane underwent restructuring upon addition of Sap C. The topographic characteristics of the membrane restructuring include the appearance of patch-like new features, initially emerged at the edge of phospholipid membranes and extended laterally with time. Changes in the image contrast of the phospholipid membrane observed after the Sap C addition indicate that a new phase of lipid-protein structure has formed during membrane restructuring. The process of membrane restructuring is dynamic, commencing shortly after Sap C addition, and continuing throughout the duration of AFM imaging (about 30 min, sometimes over 1 h). This study demonstrated the potential of AFM real-time imaging in studying protein-membrane interactions.
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Affiliation(s)
- H X You
- Department of Cell Biology, Neurobiology, and Anatomy, University of Cincinnati College of Medicine, OH 45267-0521, USA.
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Qi X, Grabowski GA. Molecular and cell biology of acid beta-glucosidase and prosaposin. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2001; 66:203-39. [PMID: 11051765 DOI: 10.1016/s0079-6603(00)66030-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- X Qi
- Children's Hospital Research Foundation, Cincinnati, Ohio 45229-3039, USA
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Salvioli R, Tatti M, Ciaffoni F, Vaccaro AM. Further studies on the reconstitution of glucosylceramidase activity by Sap C and anionic phospholipids. FEBS Lett 2000; 472:17-21. [PMID: 10781797 DOI: 10.1016/s0014-5793(00)01417-4] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The reconstitution of the activity of the lysosomal enzyme glucosylceramidase requires anionic phospholipids and, at least, a protein factor, saposin C (Sap C). We have previously proposed a mechanism for the glucosylceramidase activation [Vaccaro et al. (1993) FEBS Lett. 336, 159-162] which implies that Sap C promotes the association of the enzyme with anionic phospholipid-containing membranes, thus favoring the contact between the enzyme and its lipid substrate, glucosylceramide. We have further investigated the properties of Sap C using a fluorescent hydrophobic probe such as 4, 4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid (bis-ANS). The binding between bis-ANS and Sap C was pH-dependent, indicating that protonation leads to increased exposure of hydrophobic surfaces of Sap C. The interaction of Sap C with membranes, triggered by the development of hydrophobic properties at low pH values, was affected by the content of anionic phospholipids, such as phosphatidylserine or phosphatidylinositol, suggesting that anionic phospholipids have the potential to modulate the insertion of Sap C in the hydrophobic environment of lysosomal membranes. We previously showed that Sap C and anionic phospholipids are both required for the binding of glucosylceramidase to large vesicles. We have presently observed that Sap C is able to promote the association of glucosylceramidase with the lipid surface only when anionic phospholipids exceed a concentration of 5-10%. This level can be reached by summing lower amounts of individual anionic phospholipids, since they have additive effects. The present data extend and refine our model of the mechanism of glucosylceramidase activation and stress the key role of pH, Sap C and anionic phospholipids in promoting the interaction of the enzyme with membranes.
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Affiliation(s)
- R Salvioli
- Department of Metabolism and Pathological Biochemistry, Istituto Superiore Sanita, Viale Regina Elena 299, 00161, Rome, Italy
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40
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Grabowski GA, Horowitz M. Gaucher's disease: molecular, genetic and enzymological aspects. BAILLIERE'S CLINICAL HAEMATOLOGY 1997; 10:635-56. [PMID: 9497856 DOI: 10.1016/s0950-3536(97)80032-7] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The molecular, genetic and enzymological abnormalities in Gaucher's disease have been delineated during the past decade. Although our understanding of the primary predisposition to the Gaucher's disease phenotypes has improved, the relationships remain poorly understood between the mutant alleles, the resultant enzyme variants, the saposin C (activator protein) locus and phenotypes. Of the more than 100-disease associated alleles, about 8 to 10 have significant frequencies in various ethnic and demographic groups. The N370S(1226G) allele is very frequent in Caucasian populations, but absent in Asian groups. In the Ashkenazi Jewish population, the N370S homozygosity predisposes to Gaucher's disease, but over 50% of such patients escape medical detection because of their mild to absent involvement, i.e. N370S may be a prediposing polymorphic variant. Clarification of genotype/phenotype relationships and the identification of modifier loci that impact on Gaucher's disease phenotypes remain a critical area for research. Greater understanding of these issues will facilitate genetic counselling and appropriate interventive therapy to prevent the morbid long-term manifestations of Gaucher's disease.
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Affiliation(s)
- G A Grabowski
- University of Cincinnati College of Medicine, Children's Hospital Medical Center, Ohio 45339-3039, USA
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Vaccaro AM, Ciaffoni F, Tatti M, Salvioli R, Barca A, Tognozzi D, Scerch C. pH-dependent conformational properties of saposins and their interactions with phospholipid membranes. J Biol Chem 1995; 270:30576-80. [PMID: 8530492 DOI: 10.1074/jbc.270.51.30576] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Saposins A, B, C, and D are small lysosomal glycoproteins released by proteolysis from a single precursor polypeptide, prosaposin. We have presently investigated the conformational states of saposins and their interaction with membranes at acidic pH values similar to those present in lysosomes. With the use of phase partitioning in Triton X-114, experimental evidence was provided that, upon acidification, saposins (Sap) A, C, and D acquire hydrophobic properties, while the hydrophilicity of Sap B is apparently unchanged. The pH-dependent exposure of hydrophobic domains of Sap C and D paralleled their pH-dependent binding to large unilamellar vesicles composed of phosphatidylcholine, phosphatidylserine, and cholesterol. In contrast, the binding of Sap A to the vesicles was very restricted, in spite of its increased hydrophobicity at low pH. A low affinity for the vesicles was also shown by Sap B, a finding consistent with its apparent hydrophilicity both at neutral and acidic pH. At the acidic pH values needed for binding, Sap C and D powerfully destabilized the phospholipid membranes, while Sap A and B minimally affected the bilayer integrity. In the absence of the acidic phospholipid phosphatidylserine, the induced destabilization markedly decreased. Of the four saposins, only Sap C was able to promote the binding of glucosylceramidase to phosphatidylserine-containing membranes. This result is consistent with the notion that Sap C is specifically required by glucosylceramidase to exert its activity. Our finding that an acidic environment induces an increased hydrophobicity in Sap A, C, and D, making the last two saposins able to interact and perturb phospholipid membranes, suggests that this mechanism might be relevant to the mode of action of saposins in lysosomes.
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Affiliation(s)
- A M Vaccaro
- Department of Metabolism and Pathological Biochemistry, Istituto Superiore Sanitá, Rome, Italy
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42
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Munford RS, Sheppard PO, O'Hara PJ. Saposin-like proteins (SAPLIP) carry out diverse functions on a common backbone structure. J Lipid Res 1995. [DOI: 10.1016/s0022-2275(20)41485-3] [Citation(s) in RCA: 153] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
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43
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Vaccaro AM, Salvioli R, Barca A, Tatti M, Ciaffoni F, Maras B, Siciliano R, Zappacosta F, Amoresano A, Pucci P. Structural analysis of saposin C and B. Complete localization of disulfide bridges. J Biol Chem 1995; 270:9953-60. [PMID: 7730378 DOI: 10.1074/jbc.270.17.9953] [Citation(s) in RCA: 72] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Saposins A, B, C, and D are a group of homologous glycoproteins derived from a single precursor, prosaposin, and apparently involved in the stimulation of the enzymatic degradation of sphingolipids in lysosomes. All saposins have six cysteine residues at similar positions. In the present study we have investigated the disulfide structure of saposins B and C using advanced mass spectrometric procedures. Electrospray analysis showed that deglycosylated saposins B and C are mainly present as 79- and 80-residue monomeric polypeptides, respectively. Fast atom bombardment mass analysis of peptide mixtures obtained by a combination of chemical and enzymatic cleavages demonstrated that the pairings of the three disulfide bridges present in each saposin are Cys4-Cys77, Cys7-Cys71, Cys36-Cys47 for saposin B and Cys5-Cys78, Cys8-Cys72, Cys36-Cys47 for saposin C. We have recently shown that saposin C interacts with phosphatidylserine-containing vesicles inducing destabilization of the lipid surface (Vaccaro, A. M., Tatti, M., Ciaffoni, F., Salvioli, R., Serafino, A., and Barca, A. (1994) FEBS Lett. 349, 181-186); this perturbation promotes the binding of the lysosomal enzyme glucosylceramidase to the vesicles and the reconstitution of its activity. It was presently found that the effects of saposin C on phosphatidylserine liposomes and on glucosylceramidase activity are markedly reduced when the three disulfide bonds are irreversibly disrupted. These results stress the importance of the disulfide structure for the functional properties of the saposin.
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Affiliation(s)
- A M Vaccaro
- Laboratorio Metabolismo e Biochimica Patologica, Istituto Superiore di Sanità, Roma, Italy
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