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The Metastable XBP1u Transmembrane Domain Defines Determinants for Intramembrane Proteolysis by Signal Peptide Peptidase. Cell Rep 2020; 26:3087-3099.e11. [PMID: 30865896 DOI: 10.1016/j.celrep.2019.02.057] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 12/07/2018] [Accepted: 02/14/2019] [Indexed: 11/23/2022] Open
Abstract
Unspliced XBP1 mRNA encodes XBP1u, the transcriptionally inert variant of the unfolded protein response (UPR) transcription factor XBP1s. XBP1u targets its mRNA-ribosome-nascent-chain-complex to the endoplasmic reticulum (ER) to facilitate UPR activation and prevents overactivation. Yet, its membrane association is controversial. Here, we use cell-free translocation and cellular assays to define a moderately hydrophobic stretch in XBP1u that is sufficient to mediate insertion into the ER membrane. Mutagenesis of this transmembrane (TM) region reveals residues that facilitate XBP1u turnover by an ER-associated degradation route that is dependent on signal peptide peptidase (SPP). Furthermore, the impact of these mutations on TM helix dynamics was assessed by residue-specific amide exchange kinetics, evaluated by a semi-automated algorithm. Based on our results, we suggest that SPP-catalyzed intramembrane proteolysis of TM helices is not only determined by their conformational flexibility, but also by side-chain interactions near the scissile peptide bond with the enzyme's active site.
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2
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Keller RCA. The role and significance of potential lipid-binding regions in the mitochondrial protein import motor: an in-depth in silico study. 3 Biotech 2015; 5:1041-1051. [PMID: 28324412 PMCID: PMC4624131 DOI: 10.1007/s13205-015-0310-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2015] [Accepted: 05/12/2015] [Indexed: 12/05/2022] Open
Abstract
Over the last two decades, an impressive progress has been made in the identification of novel factors in the translocation machineries of the mitochondrial protein import and their possible roles. The role of lipids and possible protein–lipids interactions remains a relatively unexplored territory. Investigating the role of potential lipid-binding regions in the sub-units of the mitochondrial motor might help to shed some more light in our understanding of protein–lipid interactions mechanistically. Bioinformatics results seem to indicate multiple potential lipid-binding regions in each of the sub-units. The subsequent characterization of some of those regions in silico provides insight into the mechanistic functioning of this intriguing and essential part of the protein translocation machinery. Details about the way the regions interact with phospholipids were found by the use of Monte Carlo simulations. For example, Pam18 contains one possible transmembrane region and two tilted surface bound conformations upon interaction with phospholipids. The results demonstrate that the presented bioinformatics approach might be useful in an attempt to expand the knowledge of the possible role of protein–lipid interactions in the mitochondrial protein translocation process.
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Affiliation(s)
- Rob C A Keller
- Section Chemistry, Charlemagne College, Wilhelminastraat 13-15, 6524 AJ, Nijmegen, The Netherlands.
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3
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You Z, Liao M, Zhang H, Yang H, Pan X, Houghton JE, Sui SF, Tai PC. Phospholipids induce conformational changes of SecA to form membrane-specific domains: AFM structures and implication on protein-conducting channels. PLoS One 2013; 8:e72560. [PMID: 23977317 PMCID: PMC3745498 DOI: 10.1371/journal.pone.0072560] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Accepted: 07/12/2013] [Indexed: 11/23/2022] Open
Abstract
SecA, an essential component of the Sec machinery, exists in a soluble and a membrane form in Escherichia coli. Previous studies have shown that the soluble SecA transforms into pore structures when it interacts with liposomes, and integrates into membranes containing SecYEG in two forms: SecAS and SecAM; the latter exemplified by two tryptic membrane-specific domains, an N-terminal domain (N39) and a middle M48 domain (M48). The formation of these lipid-specific domains was further investigated. The N39 and M48 domains are induced only when SecA interacts with anionic liposomes. Additionally, the N-terminus, not the C-terminus of SecA is required for inducing such conformational changes. Proteolytic treatment and sequence analyses showed that liposome-embedded SecA yields the same M48 and N39 domains as does the membrane-embedded SecA. Studies with chemical extraction and resistance to trypsin have also shown that these proteoliposome-embedded SecA fragments exhibit the same stability and characteristics as their membrane-embedded SecA equivalents. Furthermore, the cloned lipid-specific domains N39 and M48, but not N68 or C34, are able to form partial, but imperfect ring-like structures when they interact with phospholipids. These ring-like structures are characteristic of a SecA pore-structure, suggesting that these domains contribute part of the SecA-dependent protein-conducting channel. We, therefore, propose a model in which SecA alone is capable of forming a lipid-specific, asymmetric dimer that is able to function as a viable protein-conducting channel in the membrane, without any requirement for SecYEG.
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Affiliation(s)
- Zhipeng You
- Department of Biology and Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, United States of America
| | - Meijiang Liao
- Department of Biology and Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, United States of America
| | - Hao Zhang
- Department of Biology and Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, United States of America
| | - Hsiuchin Yang
- Department of Biology and Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, United States of America
| | - Xijian Pan
- School of Life Sciences, Center for Structural Biology, Tsinghua University, Beijing, China
| | - John E. Houghton
- Department of Biology and Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, United States of America
| | - Sen-fang Sui
- School of Life Sciences, Center for Structural Biology, Tsinghua University, Beijing, China
| | - Phang C. Tai
- Department of Biology and Center of Biotechnology and Drug Design, Georgia State University, Atlanta, Georgia, United States of America
- * E-mail:
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4
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Prediction of Lipid-Binding Regions in Cytoplasmic and Extracellular Loops of Membrane Proteins as Exemplified by Protein Translocation Membrane Proteins. J Membr Biol 2012; 246:21-9. [DOI: 10.1007/s00232-012-9498-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2012] [Accepted: 08/18/2012] [Indexed: 02/07/2023]
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5
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Vega LA, Caparon MG. Cationic antimicrobial peptides disrupt the Streptococcus pyogenes ExPortal. Mol Microbiol 2012; 85:1119-32. [PMID: 22780862 DOI: 10.1111/j.1365-2958.2012.08163.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Although they possess a well-characterized ability to porate the bacterial membrane, emerging research suggests that cationic antimicrobial peptides (CAPs) can influence pathogen behaviour at levels that are sublethal. In this study, we investigated the interaction of polymyxin B and human neutrophil peptide (HNP-1) with the human pathogen Streptococcus pyogenes. At sublethal concentrations, these CAPs preferentially targeted the ExPortal, a unique microdomain of the S. pyogenes membrane, specialized for protein secretion and processing. A consequence of this interaction was the disruption of ExPortal organization and a redistribution of ExPortal components into the peripheral membrane. Redistribution was associated with inhibition of secretion of certain toxins, including the SpeB cysteine protease and the streptolysin O (SLO) cytolysin, but not SIC, a protein that protects S. pyogenes from CAPs. These data suggest a novel function for CAPs in targeting the ExPortal and interfering with secretion of factors required for infection and survival. This mechanism may prove valuable for the design of new types of antimicrobial agents to combat the emergence of antibiotic-resistant pathogens.
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Affiliation(s)
- Luis Alberto Vega
- Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, MO 63110-1093, USA
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6
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Hong H, Bowie JU. Dramatic destabilization of transmembrane helix interactions by features of natural membrane environments. J Am Chem Soc 2011; 133:11389-98. [PMID: 21682279 DOI: 10.1021/ja204524c] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Membrane proteins have evolved to fold and function in a lipid bilayer, so it is generally assumed that their stability should be optimized in a natural membrane environment. Yet optimal stability is not always in accord with optimization of function, so evolutionary pressure, occurring in a complex membrane environment, may favor marginal stability. Here, we find that the transmembrane helix dimer, glycophorin A (GpATM), is actually much less stable in the heterogeneous environment of a natural membrane than it is in model membranes and even common detergents. The primary destabilizing factors are electrostatic interactions between charged lipids and charged GpATM side chains, and nonspecific competition from other membrane proteins. These effects overwhelm stabilizing contributions from lateral packing pressure and excluded volume. Our work illustrates how evolution can employ membrane composition to modulate protein stability.
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Affiliation(s)
- Heedeok Hong
- Department of Chemistry and Biochemistry, UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, California 90095, USA
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7
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Romão RIS, Ferreira Q, Morgado J, Martinho JMG, Gonçalves da Silva AMPS. Microphase separation in mixed monolayers of DPPG with a double hydrophilic block copolymer at the air-water interface: a BAM, LSCFM, and AFM study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:17165-17177. [PMID: 20964300 DOI: 10.1021/la103029d] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Phase separation and interactions in mixed monolayers of dipalmitoylphosphatidylglycerol (DPPG) with the rhodamine B end-labeled double-hydrophilic block copolymer (DHBC), poly(N,N-dimethylacrylamide)-block-poly(N,N-diethylacrylamide) (RhB-PDMA(207)-b-PDEA(177)), was studied at the air-water interface. Surface pressure versus area isotherms indicate that both components behave almost independently. Brewster angle microscopy (BAM) images show a random distribution of liquid condensed (LC) domains of DPPG in an apparent homogeneous matrix of DHBC, excluding the macroscopic phase separation. The laser scanning confocal fluorescence microscopy (LSCFM) of the rhodamine dye at the end of the PDMA chain showed how the DHBC is distributed in Langmuir-Blodgett (LB) mixed monolayers. The high spatial resolution of atomic force microscopy (AFM) combined with the LCSFM images indicates that DHBC incorporates in the expanded phase of DPPG to form mixed domains, being excluded from the condensed regions. Upon compression, nanosized LC domains of DPPG nucleate inside the mixed domains corralled in the nanopatterning of pure DHBC. The negatively charged polar group of DPPG inhibits rhodamine aggregation, while the long polymer chains promote the formation of corralled nanodomains of DPPG in two dimensions.
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Affiliation(s)
- Rute I S Romão
- Centro de Química Estrutural, Instituto Superior Técnico, Avenida Rovisco Pais, P-1049-001 Lisboa, Portugal
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8
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The prediction of novel multiple lipid-binding regions in protein translocation motor proteins: a possible general feature. Cell Mol Biol Lett 2010; 16:40-54. [PMID: 20957445 PMCID: PMC6275888 DOI: 10.2478/s11658-010-0036-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2010] [Accepted: 10/12/2010] [Indexed: 11/20/2022] Open
Abstract
Protein translocation is an important cellular process. SecA is an essential protein component in the Sec system, as it contains the molecular motor that facilitates protein translocation. In this study, a bioinformatics approach was applied in the search for possible lipid-binding helix regions in protein translocation motor proteins. Novel lipid-binding regions in Escherichia coli SecA were identified. Remarkably, multiple lipid-binding sites were also identified in other motor proteins such as BiP, which is involved in ER protein translocation. The prokaryotic signal recognition particle receptor FtsY, though not a motor protein, is in many ways related to SecA, and was therefore included in this study. The results demonstrate a possible general feature for motor proteins involved in protein translocation.
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9
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Davis CH, Berkowitz ML. A molecular dynamics study of the early stages of amyloid-beta(1-42) oligomerization: the role of lipid membranes. Proteins 2010; 78:2533-45. [PMID: 20602359 DOI: 10.1002/prot.22763] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
As research progresses toward understanding the role of the amyloid-beta (Abeta) peptide in Alzheimer's disease, certain aspects of the aggregation process for Abeta are still not clear. In particular, the accepted constitution of toxic aggregates in neurons has shifted toward small oligomers. However, the process of forming these oligomers in cells is also not full clear. Even more interestingly, it has been implied that cell membranes, and, in particular, anionic lipids within those membranes, play a key role in the progression of Abeta aggregation, but the exact nature of the Abeta-membrane interaction in this process is unknown. In this work, we use a thermodynamic cycle and umbrella sampling molecular dynamics to investigate dimerization of the 42-residue Abeta peptide on model zwitterionic dipalmitoylphosphatidylcholine (DPPC) or model anionic dioleoylphosphatidylserine (DOPS) bilayer surfaces. We determined that Abeta dimerization was strongly favored through interactions with the DOPS bilayer. Further, our calculations showed that the DOPS bilayer promoted strong protein-protein interactions within the Abeta dimer, whereas DPPC favored strong protein-lipid interactions. By promoting dimer formation and subsequent dimer release into the solvent, the DOPS bilayer acts as a catalyst in Abeta aggregation.
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Affiliation(s)
- Charles H Davis
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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10
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Ding R, Li Z, Chen S, Wu D, Wu J, Chen J. Enhanced secretion of recombinant α-cyclodextrin glucosyltransferase from E. coli by medium additives. Process Biochem 2010. [DOI: 10.1016/j.procbio.2010.02.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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11
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Davis CH, Berkowitz ML. Structure of the amyloid-beta (1-42) monomer absorbed to model phospholipid bilayers: a molecular dynamics study. J Phys Chem B 2010; 113:14480-6. [PMID: 19807060 DOI: 10.1021/jp905889z] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The amyloid-beta (Abeta) peptide, the 39 to 43 amino acid peptide that plays a substantial role in Alzheimer's disease, has been shown to interact strongly with lipids both in vitro and in vivo. Abeta-lipid interactions have been proposed as a considerable factor in accelerating Abeta aggregation through the templating role of membranes in aggregation disorders. Previous work has shown that anionic lipids are able to significantly increase Abeta aggregation rate and induce a structural conversion in Abeta from a random coil to a beta-structure that is similar to the monomer structure observed in mature fibrils. However, it is unclear if this structural change occurs with the Abeta monomer because of direct interactions with the lipids or if the structural change results from protein-protein interactions during oligomerization. We use extensive replica exchange molecular dynamics simulations of an Abeta monomer bound to a homogeneous model zwitterionic or anionic lipid bilayer. From these simulations, we do not observe any significant beta-structure formation except for a small, unstable beta-hairpin formed on the anionic dioleylphosphatidylserine bilayer. Further, we see that the Asp23-Lys28 salt bridge that plays a role in beta-hairpin formation is not substantially formed on the bilayer surface and that Lys28 preferentially interacts with lipids when bound to the bilayer. These results suggest that the structural conversion seen in experiments are not due to the ordering of monomeric Abeta on the bilayer surface but are a result of protein-protein interactions enhanced by Abeta binding to the cell membrane.
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Affiliation(s)
- Charles H Davis
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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12
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Zhang J, Lazaridis T. Transmembrane helix association affinity can be modulated by flanking and noninterfacial residues. Biophys J 2009; 96:4418-27. [PMID: 19486666 DOI: 10.1016/j.bpj.2009.03.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 02/13/2009] [Accepted: 03/03/2009] [Indexed: 11/24/2022] Open
Abstract
The GxxxG sequence motif mediates the association of transmembrane (TM) helices by providing a site of close contact between them. However, it is not sufficient for strong association. For example, both bacteriophage M13 major coat protein (MCP) and human erythrocyte protein glycophorin A (GpA) contain a GxxxG motif in their TM domains and form a homodimer, but the association affinity of MCP, measured by the ToxCAT in vivo assay, is dramatically weaker than that of GpA. Even when all interfacial residues of MCP were substituted for those of GpA (MCP-GpA), association remained significantly weaker than in GpA. Here we provide an explanation for these experimental observations using molecular dynamics simulations in an implicit membrane (IMM1-GC). The association free energies of GpA29 (GpA with 29 residues all from the wild-type sequence), GpA15p11 (GpA with 15 residues from the wild-type sequence plus 11 flanking residues from the ToxCAT construct), MCP, and MCP-GpA TM helices were calculated and compared. MCP and MCP-GpA have the same flanking residues used in the ToxCAT assay as those in GpA15p11, but the position of the flanking residues relative to the GxxxG motif is different. The calculated association free energies follow experimental observations: the association affinity of MCP-GpA falls between those of GpA15p11 and MCP wild-type. MCP exhibits an equally strong interhelical interaction in the TM domain. A major reason for the weaker association of MCP in the calculations was the noninterfacial residue Lys-40, which in the dimer structure is forced to be buried in the membrane interior. To alleviate the desolvation cost, in MCP and MCP-GpA dimers, Lys-40 gets deprotonated. A second factor that modulates association affinity is the flanking residues. Thanks to them, GpA15p11 exhibits a much stronger association affinity than GpA29. The positioning of the flanking residues is also important, as evidenced by the difference in association affinity between MCP and MCP-GpA on one hand and GpA15p11 on the other. Thus, residues outside the contact interface can exert a significant influence on transmembrane helix association affinity.
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Affiliation(s)
- Jinming Zhang
- Department of Chemistry, City College of New York/CUNY, New York, NY 10031, USA
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13
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Houbiers MC, Hemminga MA. Protein-lipid interactions of bacteriophage M13 gene 9 minor coat protein (Review). Mol Membr Biol 2009; 21:351-9. [PMID: 15764365 DOI: 10.1080/09687860400012918] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Gene 9 protein is one of the minor coat proteins of bacteriophage M13. The protein plays a role in the assembly process by associating with the host membrane by protein-lipid interactions. The availability of chemically synthesized protein has enabled the biophysical characterization of the membrane-bound state of the protein by using model membrane systems. This paper summarizes, discusses and further interprets this work in the light of the current state of the literature, leading to new possible models of the coat protein in a membrane. The biological implications of these findings related to the membrane-bound phage assembly are indicated.
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Affiliation(s)
- M Chantal Houbiers
- Laboratory of Biophysics, Wageningen University, Dreijenlaan 3, NL-6703 HA Wageningen, The Netherlands
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Davis CH, Berkowitz ML. Interaction between amyloid-beta (1-42) peptide and phospholipid bilayers: a molecular dynamics study. Biophys J 2009; 96:785-97. [PMID: 19186121 DOI: 10.1016/j.bpj.2008.09.053] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Accepted: 09/24/2008] [Indexed: 01/09/2023] Open
Abstract
The amyloid-beta (Abeta) peptide is a key aggregate species in Alzheimer's disease. Although important aspects of Abeta peptide aggregation are understood, the initial stage of aggregation from monomer to oligomer is still not clear. One potential mediator of this early aggregation process is interactions of Abeta with anionic cell membranes. We used unconstrained and umbrella sampling molecular dynamics simulations to investigate interactions between the 42-amino acid Abeta peptide and model bilayers of zwitterionic dipalmitoylphosphatidylcholine (DPPC) lipids and anionic dioleoylphosphatidylserine (DOPS) lipids. Using these methods, we determined that Abeta is attracted to the surface of DPPC and DOPS bilayers over the small length scales used in these simulations. We also found supporting evidence that the charge on both the bilayer surface and the peptide affects the free energy of binding of the peptide to the bilayer surface and the distribution of the peptide on the bilayer surface. Our work demonstrates that interactions between the Abeta peptide and lipid bilayer promotes a peptide distribution on the bilayer surface that is prone to peptide-peptide interactions, which can influence the propensity of Abeta to aggregate into higher-order structures.
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Affiliation(s)
- Charles H Davis
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA.
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15
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Leal-Pinto E, Teixeira A, Tran B, Hanss B, Klotman PE. Presence of the nucleic acid channel in renal brush-border membranes: allosteric modulation by extracellular calcium. Am J Physiol Renal Physiol 2005; 289:F97-106. [PMID: 15727991 DOI: 10.1152/ajprenal.00196.2004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have previously described a cell surface channel complex that is highly selective for nucleic acid ( 6 , 7 ). The channel complex was purified to homogeneity by solubilizing renal brush-border membranes (BBM) with CHAPS and separation by liquid chromatography. It was characterized by reconstitution in planar lipid bilayers. The channel consists of a pore-forming subunit that is blocked by heparan sulfate and a regulatory subunit that is blocked by l-malate ( 7 ). The current studies were performed to compare the characteristics of the nucleic acid-conducting channel in native BBM with the characteristics that have been determined for the complex reconstituted from purified proteins. BBM were purified by differential centrifugation and reconstituted in lipid bilayers. Current was not observed until oligodeoxynucleotide (ODN) was added. Conductance was 9.1 ± 0.9 pS; rectification and voltage dependence were not observed. Reversal potential ( Erev) shifted to +14 ± 0.1 mV by a 10-fold gradient for ODN but was not altered when gradients were created for any other ion. Open probability increased significantly with an increase in Ca2+on the trans chamber of the bilayer apparatus. Changes in cis Ca2+were without effect. Addition of l-malate to the cis chamber or heparan sulfate to the trans chamber significantly reduced the open probability of the channel. These data demonstrate that the nucleic acid channel in BBM is electrophysiologically and pharmacologically identical to that previously reported for purified protein and demonstrate that a nucleic acid-conducting channel is a component of renal BBM.
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Affiliation(s)
- Edgar Leal-Pinto
- Division of Nephrology, Mt. Sinai School of Medicine, New York, NY 10029, USA
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16
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Shokri A, Larsson G. Characterisation of the Escherichia coli membrane structure and function during fedbatch cultivation. Microb Cell Fact 2004; 3:9. [PMID: 15282031 PMCID: PMC514524 DOI: 10.1186/1475-2859-3-9] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2004] [Accepted: 07/28/2004] [Indexed: 11/10/2022] Open
Abstract
Background Important parameters during recombinant protein production in Escherichia coli, such as productivity and protein activity, are affected by the growth rate. This includes the translocation of protein over the membrane to gain better folding capacity or reduced proteolysis. To vary the growth rate two techniques are available: fedbatch and continuous cultivation, both controlled by the ingoing feed rate. Results During fedbatch cultivation, E. coli contains phosphatidylethanolamine, phosphatidylglycerol, cardiolipin and saturated fatty acids in amounts which are stable with growth rate. However, the levels of cardiolipin are very high compared to continuous cultivation. The reason for fedbatch triggering of this metabolism is not known but hypothesised to result from an additional need for carbon and energy. The reason could be the dynamic and sometimes rapid changes in growth rate to which the fedbatch cell has at all times to adjust. The membrane flexibility, essential for translocation of various components, is however to some degree sustained by production of increased amounts of unsaturated fatty acids in phosphatidylglycerol. The result is a functionally stiff membrane which generally promotes low cell lysis and is constant with respect to protein leakage to the medium. At comparatively high growth rates, when the further stabilising effect of cyclic fatty acids is gone, the high level of unsaturated fatty acids results in a pronounced effect upon sonication. This is very much in contrast to the membrane function in continuous cultivation which shows very specific characteristics as a function of growth rate. Conclusions The stiff and unchanging fedbatch membrane should promote a stable behaviour during downstream processing and is less dependent on the time of harvest. However, optimisation of protein leakage can only be achieved in the continuously cultivated cell where leakage is twice as high compared to the constant leakage level in fedbatch. If leakage is undesired, continuous cultivation is also preferred since it can be designed to lead to the lowest values detected. Induction at low growth rate (<0.2 h-1) should be avoided with respect to productivity, in any system, since the specific and total protein production shows their lowest values at this point.
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Affiliation(s)
- Atefeh Shokri
- The Swedish Centre for Bioprocess Technology, Albanova University Centre, KTH SE-106 91 Stockholm, SWEDEN
| | - Gen Larsson
- The Swedish Centre for Bioprocess Technology, Albanova University Centre, KTH SE-106 91 Stockholm, SWEDEN
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17
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Wikström M, Xie J, Bogdanov M, Mileykovskaya E, Heacock P, Wieslander A, Dowhan W. Monoglucosyldiacylglycerol, a Foreign Lipid, Can Substitute for Phosphatidylethanolamine in Essential Membrane-associated Functions in Escherichia coli. J Biol Chem 2004; 279:10484-93. [PMID: 14688287 DOI: 10.1074/jbc.m310183200] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanisms by which lipid bilayer properties govern or influence membrane protein functions are little understood, but a liquid-crystalline state and the presence of anionic and nonbilayer (NB)-prone lipids seem important. An Escherichia coli mutant lacking the major membrane lipid phosphatidylethanolamine (NB-prone) requires divalent cations for viability and cell integrity and is impaired in several membrane functions that are corrected by introduction of the "foreign" NB-prone neutral glycolipid alpha-monoglucosyldiacylglycerol (MGlcDAG) synthesized by the MGlcDAG synthase from Acholeplasma laidlawii. Dependence on Mg(2+) was reduced, and cellular yields and division malfunction were greatly improved. The increased passive membrane permeability of the mutant was not abolished, but protein-mediated osmotic stress adaptation to salts and sucrose was recovered by the presence of MGlcDAG. MGlcDAG also restored tryptophan prototrophy and active transport function of lactose permease, both critically dependent on phosphatidylethanolamine. Three mechanisms can explain the observed effects: NB-prone MGlcDAG improves the quenched lateral pressure profile across the bilayer; neutral MGlcDAG dilutes the high anionic lipid surface charge; MGlcDAG provides a neutral lipid that can hydrogen bond and/or partially ionize. The reduced dependence on Mg(2+) and lack of correction by high monovalent salts strongly support the essential nature of the NB properties of MGlcDAG.
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Affiliation(s)
- Malin Wikström
- Department of Biochemistry and Biophysics, Stockholm University, Sweden
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18
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Demmers JAA, van Dalen A, de Kruijff B, Heck AJR, Killian JA. Interaction of the K+ channel KcsA with membrane phospholipids as studied by ESI mass spectrometry. FEBS Lett 2003; 541:28-32. [PMID: 12706814 DOI: 10.1016/s0014-5793(03)00282-5] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this study we have used electrospray ionization mass spectrometry (ESI-MS) to investigate interactions between the bacterial K(+) channel KcsA and membrane phospholipids. KcsA was reconstituted into lipid vesicles of variable lipid composition. These vesicles were directly analyzed by ESI-MS or mixed with trifluoroethanol (TFE) before analysis. In the resulting mass spectra, non-covalent complexes of KcsA and phospholipids were observed with an interesting lipid specificity. The anionic phosphatidylglycerol (PG), and, to a lesser extent, the zwitterionic phosphatidylethanolamine (PE), which both are abundant bacterial lipids, were found to preferentially associate with KcsA as compared to the zwitterionic phosphatidylcholine (PC). These preferred interactions may reflect the differences in affinity of these phospholipids for KcsA in the membrane.
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Affiliation(s)
- Jeroen A A Demmers
- Department of Biochemistry of Membranes, Center for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, The Netherlands.
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19
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Abstract
The presenilin-type aspartic protease signal peptide peptidase (SPP) can cleave signal peptides within their transmembrane region. SPP is essential for generation of signal peptide-derived HLA-E epitopes in humans and is exploited by Hepatitis C virus for processing of the viral polyprotein. Here we analyzed requirements of substrates for intramembrane cleavage by SPP. Comparing signal peptides that are substrates with those that are not revealed that helix-breaking residues within the transmembrane region are required for cleavage, and flanking regions can affect processing. Furthermore, signal peptides have to be liberated from the precursor protein by cleavage with signal peptidase in order to become substrates for SPP. We propose that signal peptides require flexibility in the lipid bilayer to exhibit an accessible peptide bond for intramembrane proteolysis.
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Affiliation(s)
- Marius K Lemberg
- Institute of Biochemistry, Swiss Federal Institute of Technology, ETH-Hoenggerberg, 8093, Zürich, Switzerland
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20
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Zakharov SD, Rokitskaya TI, Shapovalov VL, Antonenko YN, Cramer WA. Tuning the membrane surface potential for efficient toxin import. Proc Natl Acad Sci U S A 2002; 99:8654-9. [PMID: 12060711 PMCID: PMC124348 DOI: 10.1073/pnas.122613099] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Membrane surface electrostatic interactions impose structural constraints on imported proteins. An unprecedented sensitive dependence on these constraints was seen in the voltage-gated import and channel formation by the C-terminal pore-forming domain of the bacteriocin, colicin E1. At physiological ionic strengths, significant channel current was observed only in a narrow interval of anionic lipid content ([L-]), with the maximum current (I(max)) at 25-30 mol% (dioleoyl)-phosphatidylglycerol ([L-]max) corresponding to a surface potential of the lipid bilayer in the absence of protein, psi(o)max = -60 +/- 5 mV. Higher ionic strength shifted [L-]max to larger values, but psi(o)max remained approximately constant. It is proposed that the channel current (i) increases and (ii) decreases at /psi(o)/ values <55 mV and >65 mV, because of (i) electrostatic interactions needed for effective insertion of the channel polypeptide and (ii) constraints due to electrostatic forces on the flexibility needed for cooperative insertion into the membrane. The loss of flexibility for /psi(o)/ 65 mV was demonstrated by the absence of thermally induced intraprotein distance changes of the bound polypeptide. The anionic lipid content, 25-30 mol%, corresponding to the channel current maxima, is similar to that of the target Escherichia coli cytoplasmic membrane and membranes of mesophilic microorganisms. This suggests that one reason the membrane surface potential is tuned in vivo is to facilitate protein import.
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Affiliation(s)
- Stanislav D Zakharov
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA.
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21
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Wieprecht T, Beyermann M, Seelig J. Thermodynamics of the coil-alpha-helix transition of amphipathic peptides in a membrane environment: the role of vesicle curvature. Biophys Chem 2002; 96:191-201. [PMID: 12034440 DOI: 10.1016/s0301-4622(02)00025-x] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The binding of peptides or proteins to a bilayer membrane is often coupled with a random coil-->alpha-helix transition. Knowledge of the energetics of this membrane-induced folding event is essential for the understanding of the mechanism of membrane activity. In a recent study [Wieprecht et al., J. Mol. Biol. 294 (1999) 785-794], we have developed an approach which allows an analysis of the energetics of membrane-induced folding. We have systematically varied the helix content of the amphipathic peptide magainin-2-amide by synthesizing analogs where two adjacent amino acid residues were substituted by their corresponding D-enantiomers and have measured their binding to small unilamellar vesicles (SUVs). Correlation of the binding parameters with the helicities allowed the evaluation of the thermodynamic parameters of helix formation. Since SUVs (30 nm in diameter) are characterized by a non-ideal lipid packing due to their high membrane curvature, we have now extended our studies to large unilamellar vesicles (LUVs) (100 nm in diameter) with a lipid packing close to planar membranes. While the free energy of binding was similar for SUVs and LUVs, the binding enthalpies and entropies were distinctly different for the two membrane systems. The thermodynamic parameters of the coil-helix transition were nevertheless not affected by the vesicle size. Helix formation at the membrane surface of LUVs (SUVs) was characterized by an enthalpy change of -0.8 (-0.7) kcal/mol per residue, an entropy change of-2.3 (-1.9) cal/mol K per residue, and a free energy change of -0.12 (-0.14) kcal/mol per residue. Helix formation accounted for approximately 50% of the free energy of binding underlining its major role as a driving force for membrane-binding.
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Affiliation(s)
- Torsten Wieprecht
- Department of Biophysical Chemistry, Biozentrum University of Basel, Basel, Switzerland
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22
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Tipper DJ, Harley CA. Yeast genes controlling responses to topogenic signals in a model transmembrane protein. Mol Biol Cell 2002; 13:1158-74. [PMID: 11950929 PMCID: PMC102259 DOI: 10.1091/mbc.01-10-0488] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Yeast protein insertion orientation (PIO) mutants were isolated by selecting for growth on sucrose in cells in which the only source of invertase is a C-terminal fusion to a transmembrane protein. Only the fraction with an exocellular C terminus can be processed to secreted invertase and this fraction is constrained to 2-3% by a strong charge difference signal. Identified pio mutants increased this to 9-12%. PIO1 is SPF1, encoding a P-type ATPase located in the endoplasmic reticulum (ER) or Golgi. spf1-null mutants are modestly sensitive to EGTA. Sensitivity is considerably greater in an spf1 pmr1 double mutant, although PIO is not further disturbed. Pmr1p is the Golgi Ca(2+) ATPase and Spf1p may be the equivalent ER pump. PIO2 is STE24, a metalloprotease anchored in the ER membrane. Like Spf1p, Ste24p is expressed in all yeast cell types and belongs to a highly conserved protein family. The effects of ste24- and spf1-null mutations on invertase secretion are additive, cell generation time is increased 60%, and cells become sensitive to cold and to heat shock. Ste24p and Rce1p cleave the C-AAX bond of farnesylated CAAX box proteins. The closest paralog of SPF1 is YOR291w. Neither rce1-null nor yor291w-null mutations affected PIO or the phenotype of spf1- or ste24-null mutants. Mutations in PIO3 (unidentified) cause a weaker Pio phenotype, enhanced by a null mutation in BMH1, one of two yeast 14-3-3 proteins.
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Affiliation(s)
- Donald J Tipper
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, MA 01655, USA.
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23
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Schleiff E, Klösgen RB. Without a little help from 'my' friends: direct insertion of proteins into chloroplast membranes? BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1541:22-33. [PMID: 11750660 DOI: 10.1016/s0167-4889(01)00152-5] [Citation(s) in RCA: 67] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The chloroplast membranes are highly regulated and biological active regions of the living plant cell, which carry numerous essential proteinaceous components. For example, in the thylakoid membrane the photosynthesis apparatus, one of the most life-relevant biological machineries, is located. How these membrane proteins are targeted to and inserted into their target membranes was one of the questions we aimed to understand in the last few years. Fifteen years ago little to nothing was known about the targeting and translocation of outer envelope proteins (G.W. Schmidt and L.M. Mishkind, Annu. Rev. Biochem. 55 (1986)). Although several protein assisted pathways for translocation of proteins across the membranes have been characterised, only recent results gave insight into how membrane proteins are inserted into the chloroplast membranes. Here we will focus on the mode of insertion of a class of proteins into the outer envelope and the thylakoid membranes, which share a unique feature: they insert apparently directly into the lipid bilayer, i.e. without the help of a proteinaceous translocation pore.
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Affiliation(s)
- E Schleiff
- Department of Botany, University of Kiel, Germany
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24
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Ahn T, Kim JS, Lee BC, Yun CH. Effects of lipids on the interaction of SecA with model membranes. Arch Biochem Biophys 2001; 395:14-20. [PMID: 11673860 DOI: 10.1006/abbi.2001.2565] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The effects of nonlamellar-prone lipids, diacylglycerol and phosphatidylethanolamine (PE), on the kinetic association of SecA with model membranes were examined by measuring changes in the intrinsic emission fluorescence with a stopped-flow apparatus. Upon interaction with standard liposomes composed of 50 mol% dioleolyphosphatidylcholine (DOPC) and 50 mol% of dioleoylphosphatidylglycerol (DOPG), the intrinsic fluorescence intensity of SecA was decreased after a lapse of time with a rate constant of 0.0049 s(-1). When the DOPC of the standard vesicles was gradually replaced with either dioeloyl PE (DOPE) or Escherichia coli (E. coli) PE, the rate constant increased appreciably as a function of PE concentration, in the order DOPE > E. coli PE. In addition, when the PE of E. coli PE/DOPG (50/50) vesicles was replaced with more than 5 mol% dioleoylglycerol (DOG), the rate constant further increased by 40%. The incorporation of nonlamellar-prone lipids in the vesicles also enhanced the binding of SecA to model membranes in the order DOPE > or = E. coli PE/DOG > E. coli PE > DOPC. These results provide the first kinetic evidence for the importance of nonlamellar-prone phospholipids for the association rate of SecA with membranes.
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Affiliation(s)
- T Ahn
- Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Taejon, 305-701, Republic of Korea
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25
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Abstract
Lateral segregation in biomembranes can lead to the formation of biologically functional domains. This paper reviews atomic force microscopy studies on domain formation in model membranes, with special emphasis on transbilayer asymmetry, and on lateral domains induced by lipid-lipid interactions or by peptide-lipid interactions.
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Affiliation(s)
- H A Rinia
- Department of Biochemistry of Membranes, CBLE, Institute of Biopmembranes, Utrecht university, Netherlands.
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26
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Hessel E, Müller P, Herrmann A, Hofmann KP. Light-induced reorganization of phospholipids in rod disc membranes. J Biol Chem 2001; 276:2538-43. [PMID: 11062249 DOI: 10.1074/jbc.m009061200] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The transbilayer redistribution of spin-labeled phospholipid analogues (SL-PL) with choline, serine, and ethanolamine head groups (PC, PS, and PE, respectively) was studied on intact disc vesicles of bovine rod outer segment membranes in the dark and after illumination. Redistribution was measured by the extraction of spin-labeled lipid analogues from the outer leaflet of membrane using the bovine serum albumin back-exchange assay. In the dark, PS was distributed asymmetrically, favoring the outer leaflet, whereas PC and PE showed small if any asymmetry. Green illumination for 1 min caused lipid head group-specific reorganization of SL-PL. Extraction of SL-PS by bovine serum albumin showed a fast transient (<10 min) enhancement, which was further augmented by a peptide stabilizing the active metarhodopsin II conformation. The data suggest a direct release of 1 molecule of bound PS per rhodopsin into the outer leaflet and subsequent redistribution between the two leaflets. SL-PE and SL-PC showed more complex kinetics, in both cases consistent with a prolonged period of reduced extraction (2 phospholipids per rhodopsin in each case). The different phases of SL-PL reorganization after illumination may be related to the formation and decay of the active rhodopsin species and to their subsequent regeneration process.
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Affiliation(s)
- E Hessel
- Institut für Medizinische Physik und Biophysik, Universitätsklinikum Charité, Humboldt Universität zu Berlin, Ziegelstrabetae 5-9, Berlin D-10098, Germany.
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27
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Roux M, Beswick V, Coïc YM, Huynh-Dinh T, Sanson A, Neumann JM. PMP1 18-38, a yeast plasma membrane protein fragment, binds phosphatidylserine from bilayer mixtures with phosphatidylcholine: a (2)H-NMR study. Biophys J 2000; 79:2624-31. [PMID: 11053135 PMCID: PMC1301143 DOI: 10.1016/s0006-3495(00)76501-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
PMP1 is a 38-residue plasma membrane protein of the yeast Saccharomyces cerevisiae that regulates the activity of the H(+)-ATPase. The cytoplasmic domain conformation results in a specific interfacial distribution of five basic side chains, thought to strongly interact with anionic phospholipids. We have used the PMP1 18-38 fragment to carry out a deuterium nuclear magnetic resonance ((2)H-NMR) study for investigating the interactions between the PMP1 cytoplasmic domain and phosphatidylserines. For this purpose, mixed bilayers of 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl, 2-oleoyl-sn-glycero-3-phosphoserine (POPS) were used as model membranes (POPC/POPS 5:1, m/m). Spectra of headgroup- and chain-deuterated POPC and POPS phospholipids, POPC-d4, POPC-d31, POPS-d3, and POPS-d31, were recorded at different temperatures and for various concentrations of the PMP1 fragment. Data obtained from POPS deuterons revealed the formation of specific peptide-POPS complexes giving rise to a slow exchange between free and bound PS lipids, scarcely observed in solid-state NMR studies of lipid-peptide/protein interactions. The stoichiometry of the complex (8 POPS per peptide) was determined and its significance is discussed. The data obtained with headgroup-deuterated POPC were rationalized with a model that integrates the electrostatic perturbation induced by the cationic peptide on the negatively charged membrane interface, and a "spacer" effect due to the intercalation of POPS/PMP1f complexes between choline headgroups.
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Affiliation(s)
- M Roux
- Département de Biologie Cellulaire et Moléculaire, Section de Biophysique des Protéines et des Membranes, CEA and URA CNRS 2096, Centre d'Etudes de Saclay, 91191 Gif sur Yvette Cedex, France.
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28
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Weihofen A, Lemberg MK, Ploegh HL, Bogyo M, Martoglio B. Release of signal peptide fragments into the cytosol requires cleavage in the transmembrane region by a protease activity that is specifically blocked by a novel cysteine protease inhibitor. J Biol Chem 2000; 275:30951-6. [PMID: 10921927 DOI: 10.1074/jbc.m005980200] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Signal peptides of secretory and membrane proteins are generated by proteolytic processing of precursor proteins after insertion into the endoplasmic reticulum membrane. Liberated signal peptides can be further processed, and the resulting N-terminal fragments are released toward the cytosol, where they may interact with target proteins like calmodulin. We show here that the processing of signal peptides requires a protease activity distinct from signal peptidase. This activity is inhibited specifically with a newly developed cysteine protease inhibitor, 1, 3-di-(N-carboxybenzoyl-l-leucyl-l-leucyl)amino acetone ((Z-LL)(2) ketone). Inhibitor studies revealed that the final, (Z-LL)(2) ketone-sensitive cleavage event occurs within the hydrophobic transmembrane region of the signal peptide, thus promoting the release of an N-terminal fragment into the cytosol.
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Affiliation(s)
- A Weihofen
- Institut für Biochemie, ETH-Zentrum, Universitätstrasse 16, CH-8092 Zürich, Switzerland
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29
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Abstract
Secretion of most polypeptides across the bacterial plasma membrane is catalyzed by the Sec protein translocase. This complex molecular machine comprises a flexible transmembrane conduit coupled to a motor-like component and displays four activities: (a) it is a specific receptor at its cytoplasmic side for all secretory polypeptides, (b) it converts metabolic energy from ATP and proton gradients into mechanical motion, (c) it prevents substrates from folding in statu translocanti and (d) it binds and releases short segments of the polymeric substrate sequentially. Combination of these activities allows translocase to move processively along the length of the substrate. Substrates are thus gradually expelled from the membrane and are released for subsequent extracytoplasmic folding.
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Affiliation(s)
- A Economou
- Institute of Molecular Biology and Biotechnology-FORTH and Department of Biology, University of Crete, P.O. Box 1527, Crete GR-711 10, Iraklio, Greece.
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30
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van der Does C, Swaving J, van Klompenburg W, Driessen AJ. Non-bilayer lipids stimulate the activity of the reconstituted bacterial protein translocase. J Biol Chem 2000; 275:2472-8. [PMID: 10644701 DOI: 10.1074/jbc.275.4.2472] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To determine the phospholipid requirement of the preprotein translocase in vitro, the Escherichia coli SecYEG complex was purified in a delipidated form using the detergent dodecyl maltoside. SecYEG was reconstituted into liposomes composed of defined synthetic phospholipids, and proteoliposomes were analyzed for their preprotein translocation and SecA translocation ATPase activity. The activity strictly required the presence of anionic phospholipids, whereas the non-bilayer lipid phosphatidylethanolamine was found stimulatory. The latter effect could also be induced by dioleoylglycerol, a lipid that adopts a non-bilayer conformation. Phosphatidylethanolamine derivatives that prefer the bilayer state were unable to stimulate translocation. In the absence of SecG, activity was reduced, but the phospholipid requirement was unaltered. Remarkably, non-bilayer lipids were found essential for the activity of the Bacillus subtilis SecYEG complex. Optimal activity required a mixture of anionic and non-bilayer lipids at concentrations that correspond to concentrations found in the natural membrane.
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Affiliation(s)
- C van der Does
- Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
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31
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Buckland AG, Wilton DC. Anionic phospholipids, interfacial binding and the regulation of cell functions. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1483:199-216. [PMID: 10634937 DOI: 10.1016/s1388-1981(99)00188-2] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- A G Buckland
- Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton, UK
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32
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Wieprecht T, Apostolov O, Beyermann M, Seelig J. Thermodynamics of the alpha-helix-coil transition of amphipathic peptides in a membrane environment: implications for the peptide-membrane binding equilibrium. J Mol Biol 1999; 294:785-94. [PMID: 10610796 DOI: 10.1006/jmbi.1999.3268] [Citation(s) in RCA: 159] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Amphipathic alpha-helices are the membrane binding motif in many proteins. The corresponding peptides are often random coil in solution but are folded into an alpha-helix upon interaction with the membrane. The energetics of this ubiquitous folding process are still a matter of conjecture. Here, we present a new method to quantitatively analyze the thermodynamics of peptide folding at the membrane interface. We have systematically varied the helix content of a given amphipathic peptide when bound to the membrane and have correlated the thermodynamic binding parameters determined by isothermal titration calorimetry with the alpha-helix content obtained by circular dichroism spectroscopy. The peptides investigated were the antibiotic magainin 2 amide and three analogs in which two adjacent amino acid residues were substituted by their d-enantiomers. The thermodynamic parameters controlling the alpha-helix formation were found to be linearly related to the helicity of the membrane-bound peptides. Helix formation at the membrane surface is characterized by an enthalpy change of DeltaH(helix) approximately -0.7 kcal/mol per residue, an entropy change of DeltaS(helix) approximately -1.9 cal/molK residue and a free energy change of DeltaG(helix)=-0.14 kcal/mol residue. Helix formation is a strong driving force of peptide insertion into the membrane and accounts for about 50 % of the free energy of binding. An increase in temperature entails an unfolding of the membrane-bound helix. The temperature dependence can be described with the Zimm-Bragg theory and the enthalpy of unfolding agrees with that deduced from isothermal titration calorimetry.
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Affiliation(s)
- T Wieprecht
- Department of Biophysical Chemistry, Biocenter of the University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland
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33
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Rinia HA, Demel RA, van der Eerden JP, de Kruijff B. Blistering of langmuir-blodgett bilayers containing anionic phospholipids as observed by atomic force microscopy. Biophys J 1999; 77:1683-93. [PMID: 10465778 PMCID: PMC1300455 DOI: 10.1016/s0006-3495(99)77015-3] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Asymmetric bilayers of different phospholipid compositions have been prepared by the Langmuir-Blodgett (L-B) method, and imaged by atomic force microscopy (AFM). Such bilayers can function as a model for biological membranes. The first leaflet consisted of zwitterionic phospholipids phosphatidylcholine (PC) or phosphatidylethanolamine (PE). The second leaflet consisted of the anionic phospholipid phosphatidylglycerol (PG), in either the condensed or liquid phase or, for comparison, of PC. Different bilayers showed different morphology. In all bilayers defects in the form of holes were present. In some bilayers with a first leaflet consisting of PC, polygonal line-shaped defects were observed, whereas when the first leaflet consisted of PE, mainly round defects were seen. Not only the shape, but also the amount of defects varied, depending on the condition and the composition of the second leaflet. In most of the PG-containing systems the defects were surrounded by elevations, which reversibly disappeared in the presence of divalent cations. This is the first time that such elevations have been observed on phospholipid bilayers. We propose that they are induced by phospholipid exchange between the two leaflets around the defects, leading to the presence of negatively charged phospholipids in the first leaflet. Because the substrate is also negatively charged, the bilayer around the edges is repelled and lifted up. Since it was found that the elevations are indeed detached from the substrate, we refer to this effect as bilayer blistering.
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Affiliation(s)
- H A Rinia
- Department of Biochemistry of Membranes, Institute of Biomembranes, Centre for Biomembranes and Lipid Enzymology, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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34
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Abstract
Significant strides have been made during the past 20 years in our understanding of protein secretion across the bacterial inner membrane. Specialized chaperones select secretory polypeptide chains and usher them to a membrane-embedded preprotein translocase. This unique molecular machine envelops the polymeric substrate and migrates along its length in defined, energy-dependent steps. Consequently, preproteins are gradually pumped into the periplasm where they acquire their native, folded conformation.
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Affiliation(s)
- A Economou
- Institute of Molecular Biology and Biotechnology-FORTH, Iraklio, Crete, GR-71110, Greece.
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35
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DiRusso CC, Black PN, Weimar JD. Molecular inroads into the regulation and metabolism of fatty acids, lessons from bacteria. Prog Lipid Res 1999; 38:129-97. [PMID: 10396600 DOI: 10.1016/s0163-7827(98)00022-8] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- C C DiRusso
- Department of Biochemistry and Molecular Biology, Albany Medical College, New York, USA.
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