1
|
Xu H, Wang W, Liu X, Huang W, Zhu C, Xu Y, Yang H, Bai J, Geng D. Targeting strategies for bone diseases: signaling pathways and clinical studies. Signal Transduct Target Ther 2023; 8:202. [PMID: 37198232 DOI: 10.1038/s41392-023-01467-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2023] [Revised: 04/02/2023] [Accepted: 04/19/2023] [Indexed: 05/19/2023] Open
Abstract
Since the proposal of Paul Ehrlich's magic bullet concept over 100 years ago, tremendous advances have occurred in targeted therapy. From the initial selective antibody, antitoxin to targeted drug delivery that emerged in the past decades, more precise therapeutic efficacy is realized in specific pathological sites of clinical diseases. As a highly pyknotic mineralized tissue with lessened blood flow, bone is characterized by a complex remodeling and homeostatic regulation mechanism, which makes drug therapy for skeletal diseases more challenging than other tissues. Bone-targeted therapy has been considered a promising therapeutic approach for handling such drawbacks. With the deepening understanding of bone biology, improvements in some established bone-targeted drugs and novel therapeutic targets for drugs and deliveries have emerged on the horizon. In this review, we provide a panoramic summary of recent advances in therapeutic strategies based on bone targeting. We highlight targeting strategies based on bone structure and remodeling biology. For bone-targeted therapeutic agents, in addition to improvements of the classic denosumab, romosozumab, and PTH1R ligands, potential regulation of the remodeling process targeting other key membrane expressions, cellular crosstalk, and gene expression, of all bone cells has been exploited. For bone-targeted drug delivery, different delivery strategies targeting bone matrix, bone marrow, and specific bone cells are summarized with a comparison between different targeting ligands. Ultimately, this review will summarize recent advances in the clinical translation of bone-targeted therapies and provide a perspective on the challenges for the application of bone-targeted therapy in the clinic and future trends in this area.
Collapse
Affiliation(s)
- Hao Xu
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, Jiangsu, 215006, P. R. China
| | - Wentao Wang
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, Jiangsu, 215006, P. R. China
| | - Xin Liu
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, Jiangsu, 215006, P. R. China
| | - Wei Huang
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230031, Anhui, China
| | - Chen Zhu
- Department of Orthopedics, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, 230031, Anhui, China
| | - Yaozeng Xu
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, Jiangsu, 215006, P. R. China
| | - Huilin Yang
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, Jiangsu, 215006, P. R. China.
- Orthopaedic Institute, Medical College, Soochow University, Suzhou, 215006, Jiangsu, China.
| | - Jiaxiang Bai
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, Jiangsu, 215006, P. R. China.
- Orthopaedic Institute, Medical College, Soochow University, Suzhou, 215006, Jiangsu, China.
| | - Dechun Geng
- Department of Orthopedics, The First Affiliated Hospital of Soochow University, 188 Shizi Street, Suzhou, Jiangsu, 215006, P. R. China.
- Orthopaedic Institute, Medical College, Soochow University, Suzhou, 215006, Jiangsu, China.
| |
Collapse
|
2
|
Ahmad S, Strunk CH, Schott-Verdugo SN, Jaeger KE, Kovacic F, Gohlke H. Substrate Access Mechanism in a Novel Membrane-Bound Phospholipase A of Pseudomonas aeruginosa Concordant with Specificity and Regioselectivity. J Chem Inf Model 2021; 61:5626-5643. [PMID: 34748335 DOI: 10.1021/acs.jcim.1c00973] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
PlaF is a cytoplasmic membrane-bound phospholipase A1 from Pseudomonas aeruginosa that alters the membrane glycerophospholipid (GPL) composition and fosters the virulence of this human pathogen. PlaF activity is regulated by a dimer-to-monomer transition followed by tilting of the monomer in the membrane. However, how substrates reach the active site and how the characteristics of the active site tunnels determine the activity, specificity, and regioselectivity of PlaF for natural GPL substrates have remained elusive. Here, we combined unbiased and biased all-atom molecular dynamics (MD) simulations and configurational free-energy computations to identify access pathways of GPL substrates to the catalytic center of PlaF. Our results map out a distinct tunnel through which substrates access the catalytic center. PlaF variants with bulky tryptophan residues in this tunnel revealed decreased catalysis rates due to tunnel blockage. The MD simulations suggest that GPLs preferably enter the active site with the sn-1 acyl chain first, which agrees with the experimentally demonstrated PLA1 activity of PlaF. We propose that the acyl chain-length specificity of PlaF is determined by the structural features of the access tunnel, which results in favorable free energy of binding of medium-chain GPLs. The suggested egress route conveys fatty acid (FA) products to the dimerization interface and, thus, contributes to understanding the product feedback regulation of PlaF by FA-triggered dimerization. These findings open up opportunities for developing potential PlaF inhibitors, which may act as antibiotics against P. aeruginosa.
Collapse
Affiliation(s)
- Sabahuddin Ahmad
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany
| | - Christoph Heinrich Strunk
- Institute of Molecular Enzyme Technology, Heinrich Heine University Düsseldorf, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Stephan N Schott-Verdugo
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany.,Centro de Bioinformática y Simulación Molecular (CBSM), Faculty of Engineering, University of Talca, 3460000 Talca, Chile.,John von Neumann Institute for Computing (NIC), Jülich Supercomputing Centre (JSC), Institute of Biological Information Processing (IBI-7: Structural Biochemistry) & Institute of Bio- and Geosciences (IBG-4: Bioinformatics), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Karl-Erich Jaeger
- Institute of Molecular Enzyme Technology, Heinrich Heine University Düsseldorf, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.,Institute of Bio- and Geosciences (IBG-1: Biotechnology), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Filip Kovacic
- Institute of Molecular Enzyme Technology, Heinrich Heine University Düsseldorf, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| | - Holger Gohlke
- Institute for Pharmaceutical and Medicinal Chemistry, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany.,John von Neumann Institute for Computing (NIC), Jülich Supercomputing Centre (JSC), Institute of Biological Information Processing (IBI-7: Structural Biochemistry) & Institute of Bio- and Geosciences (IBG-4: Bioinformatics), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
| |
Collapse
|
3
|
Manna D, Cordara G, Krengel U. Crystal structure of MOA in complex with a peptide fragment: A protease caught in flagranti. Curr Res Struct Biol 2020; 2:56-67. [PMID: 34235469 PMCID: PMC8244254 DOI: 10.1016/j.crstbi.2020.04.003] [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: 12/21/2019] [Revised: 03/28/2020] [Accepted: 04/06/2020] [Indexed: 11/20/2022] Open
Abstract
The Marasmius oreades agglutinin (MOA) is the holotype of an emerging family of fungal chimerolectins and an active Ca2+/Mn2+-dependent protease, which exhibits a unique papain-like fold with special active site features. Here we investigated the functional significance of the structural elements differentiating MOA from other papain-like cysteine proteases. X-ray crystal structures of MOA co-crystallized with two synthetic substrates reveal cleaved peptides bound to the catalytic site, corresponding to the final products of the proteolytic reaction. Anomalous diffraction data on crystals grown in the presence of calcium and manganese, cadmium or zinc resolve the calcium/manganese preference of MOA and elucidate the inhibitory roles of zinc and cadmium towards papain-like cysteine proteases in general. The reported structures, together with activity data of MOA active site variants, point to a conservation of the general proteolysis mechanism established for papain. Ultimately, the findings suggest that papain and the papain-like domain of MOA are the product of convergent evolution.
Collapse
Affiliation(s)
- Dipankar Manna
- Department of Chemistry, University of Oslo, PO Box 1033 Blindern, 0315, Oslo, Norway
| | - Gabriele Cordara
- Department of Chemistry, University of Oslo, PO Box 1033 Blindern, 0315, Oslo, Norway
| | - Ute Krengel
- Department of Chemistry, University of Oslo, PO Box 1033 Blindern, 0315, Oslo, Norway
| |
Collapse
|
4
|
Carboxylic Ester Hydrolases in Bacteria: Active Site, Structure, Function and Application. CRYSTALS 2019. [DOI: 10.3390/cryst9110597] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Carboxylic ester hydrolases (CEHs), which catalyze the hydrolysis of carboxylic esters to produce alcohol and acid, are identified in three domains of life. In the Protein Data Bank (PDB), 136 crystal structures of bacterial CEHs (424 PDB codes) from 52 genera and metagenome have been reported. In this review, we categorize these structures based on catalytic machinery, structure and substrate specificity to provide a comprehensive understanding of the bacterial CEHs. CEHs use Ser, Asp or water as a nucleophile to drive diverse catalytic machinery. The α/β/α sandwich architecture is most frequently found in CEHs, but 3-solenoid, β-barrel, up-down bundle, α/β/β/α 4-layer sandwich, 6 or 7 propeller and α/β barrel architectures are also found in these CEHs. Most are substrate-specific to various esters with types of head group and lengths of the acyl chain, but some CEHs exhibit peptidase or lactamase activities. CEHs are widely used in industrial applications, and are the objects of research in structure- or mutation-based protein engineering. Structural studies of CEHs are still necessary for understanding their biological roles, identifying their structure-based functions and structure-based engineering and their potential industrial applications.
Collapse
|
5
|
Abstract
The outer membrane (OM) bilayer of Gram-negative bacteria is biologically unique in its asymmetrical organization of lipids, with an inner leaflet composed of glycerophospholipids (PLs) and a surface-exposed outer leaflet composed of lipopolysaccharide (LPS). This lipid organization is integral to the OM’s barrier properties. Perturbations of the outer leaflet by antimicrobial peptides or defects in LPS biosynthesis or transport to the OM cause a compensatory flipping of PLs to the outer leaflet. As a result, lipid asymmetry is disrupted and OM integrity is compromised. Recently, we identified an Escherichia coli mutant that exhibits aberrant accumulation of surface PLs accompanied by a cellular increase in LPS production. Remarkably, the observed hyperproduction of LPS is PldA dependent. Here we provide evidence that the fatty acids generated by PldA at the OM are transported into the cytoplasm and simultaneously activated by thioesterification to coenzyme A (CoA) by FadD. The acyl-CoAs produced ultimately inhibit LpxC degradation by FtsH. The increased levels of LpxC, the enzyme that catalyzes the first committed step in LPS biosynthesis, increases the amount of LPS produced. Our data suggest that PldA acts as a sensor for lipid asymmetry in the OM. PldA protects the OM barrier by both degrading mislocalized PLs and generating lipid second messengers that enable long-distance signaling that prompts the cell to restore homeostasis at a distant organelle. The outer membrane of Gram-negative bacteria is an effective permeability barrier that protects the cell from toxic agents, including antibiotics. Barrier defects are often manifested by phospholipids present in the outer leaflet of this membrane that take up space normally occupied by lipopolysaccharide. We have discovered a signaling mechanism that operates across the entire cell envelope used by the cell to detect these outer membrane defects. A phospholipase, PldA, that functions to degrade these mislocalized phospholipids has a second, equally important function as a sensor. The fatty acids produced by hydrolysis of the phospholipids act as second messengers to signal the cell that more lipopolysaccharide is needed. These fatty acids diffuse across the periplasm and are transported into the cytoplasm by a process that attaches coenzyme A. The acyl-CoA molecule produces signals to inhibit the degradation of the critical enzyme LpxC by the ATP-dependent protease FtsH, increasing lipopolysaccharide production.
Collapse
|
6
|
Ortiz-Suarez ML, Samsudin F, Piggot TJ, Bond PJ, Khalid S. Full-Length OmpA: Structure, Function, and Membrane Interactions Predicted by Molecular Dynamics Simulations. Biophys J 2017; 111:1692-1702. [PMID: 27760356 PMCID: PMC5071624 DOI: 10.1016/j.bpj.2016.09.009] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Revised: 08/30/2016] [Accepted: 09/06/2016] [Indexed: 12/02/2022] Open
Abstract
OmpA is a multidomain protein found in the outer membranes of most Gram-negative bacteria. Despite a wealth of reported structural and biophysical studies, the structure-function relationships of this protein remain unclear. For example, it is still debated whether it functions as a pore, and the precise molecular role it plays in attachment to the peptidoglycan of the periplasm is unknown. The absence of a consensus view is partly due to the lack of a complete structure of the full-length protein. To address this issue, we performed molecular-dynamics simulations of the full-length model of the OmpA dimer proposed by Robinson and co-workers. The N-terminal domains were embedded in an asymmetric model of the outer membrane, with lipopolysaccharide molecules in the outer leaflet and phospholipids in the inner leaflet. Our results reveal a large dimerization interface within the membrane environment, ensuring that the dimer is stable over the course of the simulations. The linker is flexible, expanding and contracting to pull the globular C-terminal domain up toward the membrane or push it down toward the periplasm, suggesting a possible mechanism for providing mechanical stability to the cell. The external loops were more stabilized than was observed in previous studies due to the extensive dimerization interface and presence of lipopolysaccharide molecules in our outer-membrane model, which may have functional consequences in terms of OmpA adhesion to host cells. In addition, the pore-gating behavior of the protein was modulated compared with previous observations, suggesting a possible role for dimerization in channel regulation.
Collapse
Affiliation(s)
- Maite L Ortiz-Suarez
- School of Chemistry, Highfield Campus, University of Southampton, Southampton, United Kingdom
| | - Firdaus Samsudin
- School of Chemistry, Highfield Campus, University of Southampton, Southampton, United Kingdom
| | - Thomas J Piggot
- School of Chemistry, Highfield Campus, University of Southampton, Southampton, United Kingdom
| | - Peter J Bond
- Bioinformatics Institute (A(∗)STAR), Singapore, Singapore; Department of Biological Sciences, National University of Singapore, Singapore, Singapore.
| | - Syma Khalid
- School of Chemistry, Highfield Campus, University of Southampton, Southampton, United Kingdom.
| |
Collapse
|
7
|
Jahangiri A, Rasooli I, Owlia P, Fooladi AAI, Salimian J. In silico design of an immunogen against Acinetobacter baumannii based on a novel model for native structure of Outer membrane protein A. Microb Pathog 2017; 105:201-210. [DOI: 10.1016/j.micpath.2017.02.028] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2016] [Revised: 02/05/2017] [Accepted: 02/20/2017] [Indexed: 11/17/2022]
|
8
|
Dufrisne MB, Petrou VI, Clarke OB, Mancia F. Structural basis for catalysis at the membrane-water interface. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:1368-1385. [PMID: 27913292 DOI: 10.1016/j.bbalip.2016.11.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Revised: 11/22/2016] [Accepted: 11/23/2016] [Indexed: 11/27/2022]
Abstract
The membrane-water interface forms a uniquely heterogeneous and geometrically constrained environment for enzymatic catalysis. Integral membrane enzymes sample three environments - the uniformly hydrophobic interior of the membrane, the aqueous extramembrane region, and the fuzzy, amphipathic interfacial region formed by the tightly packed headgroups of the components of the lipid bilayer. Depending on the nature of the substrates and the location of the site of chemical modification, catalysis may occur in each of these environments. The availability of structural information for alpha-helical enzyme families from each of these classes, as well as several beta-barrel enzymes from the bacterial outer membrane, has allowed us to review here the different ways in which each enzyme fold has adapted to the nature of the substrates, products, and the unique environment of the membrane. Our focus here is on enzymes that process lipidic substrates. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.
Collapse
Affiliation(s)
- Meagan Belcher Dufrisne
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY 10032, USA
| | - Vasileios I Petrou
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY 10032, USA
| | - Oliver B Clarke
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Filippo Mancia
- Department of Physiology and Cellular Biophysics, Columbia University, New York, NY 10032, USA.
| |
Collapse
|
9
|
May KL, Silhavy TJ. Making a membrane on the other side of the wall. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:1386-1393. [PMID: 27742351 DOI: 10.1016/j.bbalip.2016.10.004] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Revised: 09/20/2016] [Accepted: 10/04/2016] [Indexed: 12/11/2022]
Abstract
The outer membrane (OM) of Gram-negative bacteria is positioned at the frontline of the cell's interaction with its environment and provides a barrier against influx of external toxins while still allowing import of nutrients and excretion of wastes. It is a remarkable asymmetric bilayer with a glycolipid surface-exposed leaflet and a glycerophospholipid inner leaflet. Lipid asymmetry is key to OM barrier function and several different systems actively maintain this lipid asymmetry. All OM components are synthesized in the cytosol before being secreted and assembled into a contiguous membrane on the other side of the cell wall. Work in recent years has uncovered the pathways that transport and assemble most of the OM components. However, our understanding of how phospholipids are delivered to the OM remains notably limited. Here we will review seminal works in phospholipid transfer performed some 40years ago and place more recent insights in their context. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.
Collapse
Affiliation(s)
- Kerrie L May
- Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Washington Road, Princeton, NJ 08544, USA
| | - Thomas J Silhavy
- Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, Washington Road, Princeton, NJ 08544, USA.
| |
Collapse
|
10
|
Abstract
Two membranes enclose Gram-negative bacteria-an inner membrane consisting of phospholipid and an outer membrane having an asymmetric structure in which the inner leaflet contains phospholipid and the outer leaflet consists primarily of lipopolysaccharide. The impermeable nature of the outer membrane imposes a need for numerous outer membrane pores and transporters to ferry substances in and out of the cell. These outer membrane proteins have structures distinct from their inner membrane counterparts and most often function without any discernable energy source. In this chapter, we review the structures and functions of four classes of outer membrane protein: general and specific porins, specific transporters, TonB-dependent transporters, and export channels. While not an exhaustive list, these classes exemplify small-molecule transport across the outer membrane and illustrate the diversity of structures and functions found in Gram-negative bacteria.
Collapse
|
11
|
Marcoux J, Politis A, Rinehart D, Marshall DP, Wallace MI, Tamm LK, Robinson CV. Mass spectrometry defines the C-terminal dimerization domain and enables modeling of the structure of full-length OmpA. Structure 2014; 22:781-90. [PMID: 24746938 DOI: 10.1016/j.str.2014.03.004] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2014] [Revised: 02/26/2014] [Accepted: 03/17/2014] [Indexed: 11/17/2022]
Abstract
The transmembrane domain of the outer membrane protein A (OmpA) from Escherichia coli is an excellent model for structural and folding studies of β-barrel membrane proteins. However, full-length OmpA resists crystallographic efforts, and the link between its function and tertiary structure remains controversial. Here we use site-directed mutagenesis and mass spectrometry of different constructs of OmpA, released in the gas phase from detergent micelles, to define the minimal region encompassing the C-terminal dimer interface. Combining knowledge of the location of the dimeric interface with molecular modeling and ion mobility data allows us to propose a low-resolution model for the full-length OmpA dimer. Our model of the dimer is in remarkable agreement with experimental ion mobility data, with none of the unfolding or collapse observed for full-length monomeric OmpA, implying that dimer formation stabilizes the overall structure and prevents collapse of the flexible linker that connects the two domains.
Collapse
Affiliation(s)
- Julien Marcoux
- Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, UK
| | - Argyris Politis
- Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, UK
| | - Dennis Rinehart
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, USA
| | - David P Marshall
- Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, UK
| | - Mark I Wallace
- Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, UK
| | - Lukas K Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA 22908, USA
| | - Carol V Robinson
- Chemistry Research Laboratory, University of Oxford, Oxford OX1 3TA, UK.
| |
Collapse
|
12
|
Efficient production of extracellular proteins with Escherichia coli by means of optimized coexpression of bacteriocin release proteins. J Biotechnol 2010; 145:350-8. [DOI: 10.1016/j.jbiotec.2009.11.019] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Revised: 11/08/2009] [Accepted: 11/24/2009] [Indexed: 11/19/2022]
|
13
|
Bishop RE. Structural biology of membrane-intrinsic beta-barrel enzymes: sentinels of the bacterial outer membrane. BIOCHIMICA ET BIOPHYSICA ACTA 2008; 1778:1881-96. [PMID: 17880914 PMCID: PMC5007122 DOI: 10.1016/j.bbamem.2007.07.021] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2007] [Revised: 06/28/2007] [Accepted: 07/24/2007] [Indexed: 02/06/2023]
Abstract
The outer membranes of Gram-negative bacteria are replete with integral membrane proteins that exhibit antiparallel beta-barrel structures, but very few of these proteins function as enzymes. In Escherichia coli, only three beta-barrel enzymes are known to exist in the outer membrane; these are the phospholipase OMPLA, the protease OmpT, and the phospholipidColon, two colonslipid A palmitoyltransferase PagP, all of which have been characterized at the structural level. Structural details have also emerged for the outer membrane beta-barrel enzyme PagL, a lipid A 3-O-deacylase from Pseudomonas aeruginosa. Lipid A can be further modified in the outer membrane by two beta-barrel enzymes of unknown structure; namely, the Salmonella enterica 3'-acyloxyacyl hydrolase LpxR, and the Rhizobium leguminosarum oxidase LpxQ, which employs O(2) to convert the proximal glucosamine unit of lipid A into 2-aminogluconate. Structural biology now indicates how beta-barrel enzymes can function as sentinels that remain dormant when the outer membrane permeability barrier is intact. Host immune defenses and antibiotics that perturb this barrier can directly trigger beta-barrel enzymes in the outer membrane. The ensuing adaptive responses occur instantaneously and rapidly outpace other signal transduction mechanisms that similarly function to restore the outer membrane permeability barrier.
Collapse
Affiliation(s)
- Russell E Bishop
- Department of Biochemistry and Biomedical Sciences, 1200 Main Street West, Health Sciences Centre 4H19, McMaster University, Hamilton, ON, Canada L8N 3Z5.
| |
Collapse
|
14
|
Istivan TS, Smith SC, Fry BN, Coloe PJ. Characterization of Campylobacter concisus hemolysins. ACTA ACUST UNITED AC 2008; 54:224-35. [PMID: 18754784 DOI: 10.1111/j.1574-695x.2008.00467.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Campylobacter concisus is an opportunistic pathogen commonly found in the human oral cavity. It has also been isolated from clinical sources including gastroenteritis cases. Both secreted and cell-associated hemolytic activities were detected in C. concisus strains isolated from children with gastroenteritis. The secreted hemolytic activity of C. concisus strains was labile and was detected in variable levels from fresh-culture filtrates only. In addition, another secreted hemolysin/cytotoxin with a molecular weight < 10 kDa was detected in a single C. concisus strain (RCH 12). A C. concisus genomic library, constructed from strain RCH 3 in Escherichia coli XL1-Blue, was screened for hemolytic clones. Subcloning and sequence analysis of selected hemolytic clones identified ORFs for genes that enhance hemolytic activity but do not appear to be related to any known hemolysin genes found in Gram-negative bacteria. In a previous study, a stable cell-associated hemolysin was identified as an outer-membrane phospholipase A (OMPLA) encoded by the pldA gene. In this study, we report cloning of the pldA gene of the clinical strain C. concisus RCH 3 and the complementation of phospholipase A activity in an E. coli pldA mutant.
Collapse
|
15
|
Dell’Orco D, Casciari D, Fanelli F. Quaternary structure predictions and estimation of mutational effects on the free energy of dimerization of the OMPLA protein. J Struct Biol 2008; 163:155-62. [DOI: 10.1016/j.jsb.2008.05.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2008] [Revised: 05/01/2008] [Accepted: 05/02/2008] [Indexed: 10/22/2022]
|
16
|
Laurencin D, Wong A, Hanna JV, Dupree R, Smith ME. A High-Resolution 43Ca Solid-State NMR Study of the Calcium Sites of Hydroxyapatite. J Am Chem Soc 2008; 130:2412-3. [DOI: 10.1021/ja710557t] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Danielle Laurencin
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom, and ANSTO NMR Facility, Menai 2234, New South Wales, Australia
| | - Alan Wong
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom, and ANSTO NMR Facility, Menai 2234, New South Wales, Australia
| | - John V. Hanna
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom, and ANSTO NMR Facility, Menai 2234, New South Wales, Australia
| | - Ray Dupree
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom, and ANSTO NMR Facility, Menai 2234, New South Wales, Australia
| | - Mark E. Smith
- Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom, and ANSTO NMR Facility, Menai 2234, New South Wales, Australia
| |
Collapse
|
17
|
Istivan TS, Coloe PJ. Phospholipase A in Gram-negative bacteria and its role in pathogenesis. MICROBIOLOGY-SGM 2006; 152:1263-1274. [PMID: 16622044 DOI: 10.1099/mic.0.28609-0] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Phospholipase A (PLA) is one of the few enzymes present in the outer membrane of Gram-negative bacteria, and is likely to be involved in the membrane disruption processes that occur during host cell invasion. Both secreted and membrane-bound phospholipase A(2) activities have been described in bacteria, fungi and protozoa. Recently there have been increasing reports on the involvement of PLA in bacterial invasion and pathogenesis. This review highlights the latest findings on PLA as a virulence factor in Gram-negative bacteria.
Collapse
Affiliation(s)
- Taghrid S Istivan
- Biotechnology and Environmental Biology, School of Applied Sciences, RMIT University, Bundoora West Campus, PO Box 71, Bundoora, Melbourne, VIC 3083, Australia
| | - Peter J Coloe
- Biotechnology and Environmental Biology, School of Applied Sciences, RMIT University, Bundoora West Campus, PO Box 71, Bundoora, Melbourne, VIC 3083, Australia
| |
Collapse
|
18
|
Reynolds CM, Ribeiro AA, McGrath SC, Cotter RJ, Raetz CRH, Trent MS. An outer membrane enzyme encoded by Salmonella typhimurium lpxR that removes the 3'-acyloxyacyl moiety of lipid A. J Biol Chem 2006; 281:21974-21987. [PMID: 16704973 PMCID: PMC2702521 DOI: 10.1074/jbc.m603527200] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Salmonella and related bacteria modify the structure of the lipid A portion of their lipopolysaccharide in response to environmental stimuli. Some lipid A modifications are required for virulence and resistance to cationic antimicrobial peptides. We now demonstrate that membranes of Salmonella typhimurium contain a novel hydrolase that removes the 3'-acyloxyacyl residue of lipid A in the presence of 5 mM Ca2+. We have identified the gene encoding the S. typhimurium lipid A 3'-O-deacylase, designated lpxR, by screening an ordered S. typhimurium genomic DNA library, harbored in Escherichia coli K-12, for expression of Ca2+-dependent 3'-O-deacylase activity in membranes. LpxR is synthesized with an N-terminal type I signal peptide and is localized to the outer membrane. Mass spectrometry was used to confirm the position of lipid A deacylation in vitro and the release of the intact 3'-acyloxyacyl group. Heterologous expression of lpxR in the E. coli K-12 W3110, which lacks lpxR, resulted in production of significant amounts of 3'-O-deacylated lipid A in growing cultures. Orthologues of LpxR are present in the genomes of E. coli O157:H7, Yersinia enterocolitica, Helicobacter pylori, and Vibrio cholerae. The function of LpxR is unknown, but it could play a role in pathogenesis because it might modulate the cytokine response of an infected animal.
Collapse
Affiliation(s)
- C Michael Reynolds
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710
| | - Anthony A Ribeiro
- Duke NMR Spectroscopy Center and Department of Radiology, Duke University Medical Center, Durham, North Carolina 27710
| | - Sara C McGrath
- Middle Atlantic Mass Spectrometry Laboratory, Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Robert J Cotter
- Middle Atlantic Mass Spectrometry Laboratory, Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Christian R H Raetz
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina 27710.
| | - M Stephen Trent
- Department of Microbiology, J. H. Quillen College of Medicine, East Tennessee State University, Johnson City, Tennessee 37614.
| |
Collapse
|
19
|
Wright CS, Mi LZ, Lee S, Rastinejad F. Crystal Structure Analysis of Phosphatidylcholine−GM2-Activator Product Complexes: Evidence for Hydrolase Activity,. Biochemistry 2005; 44:13510-21. [PMID: 16216074 DOI: 10.1021/bi050668w] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
GM2-activator protein (GM2AP) is a lysosomal lipid transfer protein with important biological roles in ganglioside catabolism, phospholipid metabolism, and T-cell activation. Previous studies of crystal structures of GM2AP complexed with the physiological ligand GM2 and platelet activating factor (PAF) have shown binding at two specific locations within the spacious apolar pocket and an ordering effect of endogenous resident lipids. To investigate the structural basis of phospholipid binding further, GM2AP was cocrystallized with phosphatidylcholine (PC), known to interact with GM2AP. Analysis of three crystal forms revealed binding of single chain lipids and fatty acids only and surprisingly not intact PC. The regions of best defined electron density are consistent with the presence of lyso-PC and oleic acid, which constitute deacylation products of PC. Their acyl tails are in stacking contact with shorter, less well-defined stretches of electron density that may represent resident fatty acids. The GM2AP associated hydrolytic activity that generates lyso-PC was further confirmed by mass spectrometry and enzymatic assays. In addition, we report the structures of (i) mutant Y137S, assessing the role of Tyr137 in lipid transfer via the hydrophobic cleft, and (ii) apo-mouse GM2AP, revealing a hydrophobic pocket with a constricted opening. Our structural results provide new insights into the biological functions of GM2AP. The combined effect of hydrolytic and lipid transfer properties has profound implications in cellular signaling.
Collapse
Affiliation(s)
- Christine S Wright
- Department of Pharmacology, X-ray Crystallography Laboratory, University of Virginia, Charlottesville, Virginia 22908-0735, USA.
| | | | | | | |
Collapse
|
20
|
Tannaes T, Bukholm G. Cholesteryl-6-O-acyl-α-d-glucopyranoside ofHelicobacter pylorirelate to relative lysophospholipid content. FEMS Microbiol Lett 2005; 244:117-20. [PMID: 15727830 DOI: 10.1016/j.femsle.2005.01.030] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Revised: 01/11/2005] [Accepted: 01/17/2005] [Indexed: 11/26/2022] Open
Abstract
The presence of cholesteryl glucosides and high levels of lysophospholipids are elements making the cell wall of Helicobacter pylori unique. In this study, we have investigated the relationship between lysophospholipid content and cholesteryl glucoside composition of variants of 6 clinical isolates. The samples were characterized by diverse outer membrane phospholipase A activity measured as lysophospholipid content of the cell wall. A pldA negative mutant was also included in the study. Thin-layer chromatography showed that cholesteryl glucosides were present in all samples. However, the distribution of cholesteryl-6-O-acyl-alpha-D-glucopyranoside, cholesteryl-alpha-D-glucopyranoside and cholesteryl-6-O-phosphatidyl-alpha-D-glucopyranoside varied according to lysophospholipid content. Cholesteryl-6-O-acyl-alpha-D-glucopyranoside was exclusively observed in the isolates/variants with an intact pldA and where a significant amount of lysophospholipids could be demonstrated. High lysophospholipid content destabilizes membranes. The balance between cholesteryl-6-O-acyl-alpha-D-glucopyranoside, cholesteryl-alpha-D-glucopyranoside and cholesteryl-6-O-phosphatidyl-alpha-D-glucopyranoside in H. pylori is probably important for the stability of the membrane when the lysophospholipid content varies.
Collapse
Affiliation(s)
- Tone Tannaes
- Institute of Clinical Epidemiology and Molecular Biology, University of Oslo, Akershus University Hospital, Lørenskog, Norway.
| | | |
Collapse
|
21
|
Bigelow HR, Petrey DS, Liu J, Przybylski D, Rost B. Predicting transmembrane beta-barrels in proteomes. Nucleic Acids Res 2004; 32:2566-77. [PMID: 15141026 PMCID: PMC419468 DOI: 10.1093/nar/gkh580] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Very few methods address the problem of predicting beta-barrel membrane proteins directly from sequence. One reason is that only very few high-resolution structures for transmembrane beta-barrel (TMB) proteins have been determined thus far. Here we introduced the design, statistics and results of a novel profile-based hidden Markov model for the prediction and discrimination of TMBs. The method carefully attempts to avoid over-fitting the sparse experimental data. While our model training and scoring procedures were very similar to a recently published work, the architecture and structure-based labelling were significantly different. In particular, we introduced a new definition of beta- hairpin motifs, explicit state modelling of transmembrane strands, and a log-odds whole-protein discrimination score. The resulting method reached an overall four-state (up-, down-strand, periplasmic-, outer-loop) accuracy as high as 86%. Furthermore, accurately discriminated TMB from non-TMB proteins (45% coverage at 100% accuracy). This high precision enabled the application to 72 entirely sequenced Gram-negative bacteria. We found over 164 previously uncharacterized TMB proteins at high confidence. Database searches did not implicate any of these proteins with membranes. We challenge that the vast majority of our 164 predictions will eventually be verified experimentally. All proteome predictions and the PROFtmb prediction method are available at http://www.rostlab.org/ services/PROFtmb/.
Collapse
Affiliation(s)
- Henry R Bigelow
- CUBIC, Department of Biochemistry and Molecular Biophysics, Columbia University, 650 West 168th Street BB217, New York, NY 10032, USA.
| | | | | | | | | |
Collapse
|
22
|
Baaden M, Meier C, Sansom MSP. A molecular dynamics investigation of mono and dimeric states of the outer membrane enzyme OMPLA. J Mol Biol 2003; 331:177-89. [PMID: 12875844 DOI: 10.1016/s0022-2836(03)00718-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
OMPLA is a phospholipase found in the outer membranes of many Gram-negative bacteria. Enzyme activation requires calcium-induced dimerisation plus bilayer perturbation. As the conformation of OMPLA in the different crystal forms (monomer versus dimer; with/without bound Ca(2+)) is remarkably similar we have used multi-nanosecond molecular dynamics (MD) simulations to probe possible differences in conformational dynamics that may be related to enzyme activation. Simulations of calcium-free monomeric OMPLA, of the Ca(2+)-bound dimer, and of the Ca(2+)-bound dimer with a substrate analogue covalently linked to the active site serine have been performed, all with the protein embedded in a phospholipid (POPC) bilayer. All simulations were stable, but differences in the dynamic behaviour of the protein between the various states were observed. In particular, the stability of the active site and the hydrophobic substrate-binding cleft varied. Dimeric OMPLA is less flexible than monomeric OMPLA, especially around the active site. In the absence of bound substrate analogue, the hydrophobic substrate-binding cleft of dimeric OMPLA collapses. A model is proposed whereby the increased stability of the active site in dimeric OMPLA is a consequence of the local ordering of water around the nearby calcium ion. The observed collapse of the substrate-binding cleft may explain the experimentally observed occurrence of multiple dimer conformations of OMPLA, one of which is fully active while the other shows significantly reduced activity.
Collapse
Affiliation(s)
- Marc Baaden
- Department of Biochemistry, University of Oxford, South Parks Road Oxford, OX1 3QU, UK
| | | | | |
Collapse
|
23
|
Abstract
Using a lysine-specific cleavable cross-linking reagent ethylene glycolbis(sulfosuccimidylsuccinate) (Sulfo-EGS), we studied conformational motion in the surface loops of Escherichia coli FepA during its transport of the siderophore ferric enterobactin. Site-directed mutagenesis determined that Sulfo-EGS reacted with two lysines, K332 and K483, and at least two other unidentified Lys residues in the surface loops of the outer membrane protein. The reagent cross-linked K483 in FepA L7 to either K332 in L5, forming a product that we designated band 1, or to the major outer membrane proteins OmpF, OmpC, and OmpA, forming band 2. Ferric enterobactin binding to FepA did not prevent modification of K483 by Sulfo-EGS but blocked its cross-linking to OmpF/C and OmpA and reduced its coupling to K332. These data show that the loops of FepA undergo conformational changes in vivo, with an approximate magnitude of 15 A, from a ligand-free open state to a ligand-bound closed state. The coupling of FepA L7 to OmpF, OmpC, or OmpA was TonB independent and was unaffected by the uncouplers CCCP (carbonyl cyanide m-chlorophenylhydrazone) and DNP (2,4-dinitrophenol) but completely inhibited by cyanide.
Collapse
Affiliation(s)
- Daniel C Scott
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA
| | | | | |
Collapse
|
24
|
Abstract
To kill Escherichia coli, toxic proteins, called colicins, pass through the permeability barrier created by the outer membrane (OM) of the bacterial cell envelope. We consider a variety of different colicins, including A, B, D, E1, E3, Ia, M and N, that penetrate through the porins OmpF, FepA, BtuB, Cir and FhuA, to subsequently interact with a few targets in the periplasm, including TolA, TolB, TolC and TonB. We review the mechanisms, demonstrated and postulated, by which such toxins enter bacterial cells, from the initial binding stage on the cell surface to the internalization reaction through the OM bilayer. Our discussions endeavor to answer two main questions: what is the origin of colicin-binding affinity and specificity, and after adsorption to OM porins, do colicin polypeptides translocate through porin channels, or enter by another, currently unknown pathway?
Collapse
Affiliation(s)
- Zhenghua Cao
- Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Norman, OK 73019, USA
| | | |
Collapse
|
25
|
Kingma RL, Snijder HJ, Dijkstra BW, Dekker N, Egmond MR. Functional importance of calcium binding sites in outer membrane phospholipase A. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1561:230-7. [PMID: 11997123 DOI: 10.1016/s0005-2736(02)00351-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Outer membrane phospholipase A (OMPLA) is an integral membrane enzyme that hydrolyses phospholipids requiring Ca(2+) as cofactor. In vitro studies have shown that OMPLA is only active as a dimer. The structures of monomeric and dimeric OMPLA provided possible clues to the activation process. In the inhibited dimeric species calcium ions are located at the dimer interface ideally suited to stabilise the oxyanion intermediates formed during catalysis. The side chain hydroxyl function of Ser152 is one of the ligands of this interfacial calcium. In the crystal structure of monomeric OMPLA the interfacial calcium site is lacking, but calcium was found to bind at a site involving the carboxylates of Asp149 and Asp184. In the current study the relevance of the identified calcium sites has been studied by site-directed mutagenesis. The Ser152Asn variant confirmed the importance of the interfacial calcium site for catalysis, and also demonstrated that this site is essentially involved in the dimerisation process. Replacements of the ligands in monomeric OMPLA, i.e. Asp149Asn, Asp149Ala and Asp184Asn, only showed minor effects on catalytic activity and dimerisation. A stronger effect observed for the variant Asp184Ala was explained by the proximity of Asp184 to the catalytically important Ser152 residue. We propose that Asp149 and Asp184 provide an electronegative funnel that may facilitate Ca(2+) transfer to the interfacial calcium site.
Collapse
Affiliation(s)
- Roelie L Kingma
- Department of Membrane Enzymology, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, P.O. Box 80054, 3508 TB Utrecht, Netherlands
| | | | | | | | | |
Collapse
|
26
|
Abstract
Outer membrane phospholipase A (OMPLA) activity is regulated by reversible dimerisation with the dimer being the active species. Observed lag phases in activity indicated that dimerisation may be slow relative to turnover. A covalent OMPLA dimer indeed did not display lag phase behaviour. A model for OMPLA kinetics was proposed accounting for a slow dimerisation step. Preincubation conditions determined the initial amount of monomer and influenced both lag times and final activities. Under the conditions used, substrate concentrations higher than 50 mol% inhibited OMPLA activity and increased lag times. Our results may shed more light on mechanisms controlling OMPLA activity in vivo.
Collapse
Affiliation(s)
- Roelie L Kingma
- Department of Membrane Enzymology, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
| | | |
Collapse
|
27
|
Kingma RL, Egmond MR. Activation of a covalent outer membrane phospholipase A dimer. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:2178-85. [PMID: 11985596 DOI: 10.1046/j.1432-1033.2002.02873.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The activity of outer membrane phospholipase A (OMPLA) is regulated by reversible dimerization. However, native OMPLA reconstituted in phospholipid vesicles was found to be present as a dimer but nevertheless inactive. To investigate the importance of dimerization for control of OMPLA activity, a covalent OMPLA dimer was constructed and its properties were compared to native OMPLA both in a micellar detergent and after reconstitution in a phospholipid bilayer. Unlike native OMPLA, activity of the covalent OMPLA dimer was independent of type and concentration of detergent in micellar systems. In such systems, the covalent OMPLA dimer invariantly displayed high calcium affinity. In contrast, high calcium concentrations were required to activate a covalent OMPLA dimer when present in intact vesicles. Solubilization of the vesicles increased the affinity for calcium, suggesting that in an intact bilayer the dimer interface is not properly formed. This was supported by the observation that OMPLA variants having an impaired dimeric interface also lacked high affinity calcium binding. A covalent linkage was not able to restore high affinity calcium binding in these variants, demonstrating that a proper dimer interface is essential for optimal catalysis.
Collapse
Affiliation(s)
- Roelie L Kingma
- Department of Membrane Enzymology, Centre for Biomembranes and Lipid Enzymology, Institute of Biomembranes, Utrecht University, the Netherlands
| | | |
Collapse
|
28
|
Snijder HJ, Van Eerde JH, Kingma RL, Kalk KH, Dekker N, Egmond MR, Dijkstra BW. Structural investigations of the active-site mutant Asn156Ala of outer membrane phospholipase A: function of the Asn-His interaction in the catalytic triad. Protein Sci 2001; 10:1962-9. [PMID: 11567087 PMCID: PMC2374211 DOI: 10.1110/ps.17701] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Outer membrane phospholipase A (OMPLA) from Escherichia coli is an integral-membrane enzyme with a unique His-Ser-Asn catalytic triad. In serine proteases and serine esterases usually an Asp occurs in the catalytic triad; its role has been the subject of much debate. Here the role of the uncharged asparagine in the active site of OMPLA is investigated by structural characterization of the Asn156Ala mutant. Asparagine 156 is not involved in maintaining the overall active-site configuration and does not contribute significantly to the thermal stability of OMPLA. The active-site histidine retains an active conformation in the mutant notwithstanding the loss of the hydrogen bond to the asparagine side chain. Instead, stabilization of the correct tautomeric form of the histidine can account for the observed decrease in activity of the Asn156Ala mutant.
Collapse
Affiliation(s)
- H J Snijder
- Laboratory of Biophysical Chemistry, BIOSON Research Institute, University of Groningen, 9747 AG Groningen, The Netherlands
| | | | | | | | | | | | | |
Collapse
|