151
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Willis LM, Whitfield C. Structure, biosynthesis, and function of bacterial capsular polysaccharides synthesized by ABC transporter-dependent pathways. Carbohydr Res 2013; 378:35-44. [PMID: 23746650 DOI: 10.1016/j.carres.2013.05.007] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Revised: 05/06/2013] [Accepted: 05/11/2013] [Indexed: 12/11/2022]
Abstract
Bacterial capsules are formed primarily from long-chain polysaccharides with repeat-unit structures. A given bacterial species can produce a range of capsular polysaccharides (CPSs) with different structures and these help distinguish isolates by serotyping, as is the case with Escherichia coli K antigens. Capsules are important virulence factors for many pathogens and this review focuses on CPSs synthesized via ATP-binding cassette (ABC) transporter-dependent processes in Gram-negative bacteria. Bacteria utilizing this pathway are often associated with urinary tract infections, septicemia, and meningitis, and E. coli and Neisseria meningitidis provide well-studied examples. CPSs from ABC transporter-dependent pathways are synthesized at the cytoplasmic face of the inner membrane through the concerted action of glycosyltransferases before being exported across the inner membrane and translocated to the cell surface. A hallmark of these CPSs is a conserved reducing terminal glycolipid composed of phosphatidylglycerol and a poly-3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) linker. Recent discovery of the structure of this conserved lipid terminus provides new insights into the early steps in CPS biosynthesis.
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Affiliation(s)
- Lisa M Willis
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
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152
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Bushell S, Mainprize I, Wear M, Lou H, Whitfield C, Naismith J. Wzi is an outer membrane lectin that underpins group 1 capsule assembly in Escherichia coli. Structure 2013; 21:844-53. [PMID: 23623732 PMCID: PMC3791409 DOI: 10.1016/j.str.2013.03.010] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Revised: 03/19/2013] [Accepted: 03/20/2013] [Indexed: 12/12/2022]
Abstract
Many pathogenic bacteria encase themselves in a polysaccharide capsule that provides a barrier to the physical and immunological challenges of the host. The mechanism by which the capsule assembles around the bacterial cell is unknown. Wzi, an integral outer-membrane protein from Escherichia coli, has been implicated in the formation of group 1 capsules. The 2.6 Å resolution structure of Wzi reveals an 18-stranded β-barrel fold with a novel arrangement of long extracellular loops that blocks the extracellular entrance and a helical bundle that plugs the periplasmic end. Mutagenesis shows that specific extracellular loops are required for in vivo capsule assembly. The data show that Wzi binds the K30 carbohydrate polymer and, crucially, that mutants functionally deficient in vivo show no binding to K30 polymer in vitro. We conclude that Wzi is a novel outer-membrane lectin that assists in the formation of the bacterial capsule via direct interaction with capsular polysaccharides.
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Affiliation(s)
- Simon R. Bushell
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews, KY16 9ST, UK
| | - Iain L. Mainprize
- Department of Molecular & Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Martin A. Wear
- School of Chemistry, King’s Buildings, University of Edinburgh, Edinburgh, EH9 3JJ, UK
| | - Hubing Lou
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews, KY16 9ST, UK
| | - Chris Whitfield
- Department of Molecular & Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - James H. Naismith
- Biomedical Sciences Research Complex, University of St Andrews, St Andrews, KY16 9ST, UK
- Corresponding author
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153
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Yuan B, Cheng A, Wang M. Polysaccharide export outer membrane proteins in Gram-negative bacteria. Future Microbiol 2013; 8:525-35. [DOI: 10.2217/fmb.13.13] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Polysaccharide export outer membrane proteins of Gram-negative bacteria are involved in the export of polysaccharides across the outer membrane. The mechanisms of polysaccharide export across the outer membrane in Gram-negative bacteria are not yet completely clear. However, the mechanisms of polysaccharide assembly in Escherichia coli have been intensively investigated. Here, we mainly review the current understanding of the assembly mechanisms of group 1 capsular polysaccharide, group 2 capsular polysaccharide and lipopolysaccharide of E. coli, and the current structures and interactions of some polysaccharide export outer membrane proteins with other proteins involved in polysaccharide export in Gram-negative bacteria. In addition, LptD may be targeted by peptidomimetic antibiotics in Gram-negative bacteria. We also give insights into the directions of future research regarding the mechanisms of polysaccharide export.
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Affiliation(s)
- Biao Yuan
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan 611130, China.
| | - Anchun Cheng
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan 611130, China
- Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, 46 Xinkang Road, Ya’an, Sichuan 625014, China
- Key Laboratory of Animal Disease & Human Health of Sichuan Province, Sichuan Agricultural University, Wenjiang, Chengdu city, Sichuan 611130, China
| | - Mingshu Wang
- Institute of Preventive Veterinary Medicine, Sichuan Agricultural University, Wenjiang, Chengdu City, Sichuan 611130, China
- Avian Disease Research Center, College of Veterinary Medicine of Sichuan Agricultural University, 46 Xinkang Road, Ya’an, Sichuan 625014, China
- Key Laboratory of Animal Disease & Human Health of Sichuan Province, Sichuan Agricultural University, Wenjiang, Chengdu city, Sichuan 611130, China
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154
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Vera M, Krok B, Bellenberg S, Sand W, Poetsch A. Shotgun proteomics study of early biofilm formation process of Acidithiobacillus ferrooxidans ATCC 23270 on pyrite. Proteomics 2013; 13:1133-44. [PMID: 23319327 DOI: 10.1002/pmic.201200386] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2012] [Revised: 12/17/2012] [Accepted: 12/18/2012] [Indexed: 12/15/2022]
Abstract
Acidithiobacillus ferrooxidans is a chemolithoautotrophic, mesophilic Gram-negative bacterium able to oxidize ferrous iron, sulfur, and metal sulfides. It forms monolayer biofilms where extracellular polymeric substances are essential for cell attachment and metal sulfide leaching. High-throughput proteomics has been applied to study the early process of biofilm formation on pyrite by At. ferrooxidans ATCC 23270. After 24 h contact with the mineral, planktonic and sessile (biofilm) cell subpopulations were separated and proteins extracted. In total, 1319 proteins were detected in both samples. Sixty-two of these were found to be increased in biofilms. Additionally, 25 proteins were found to be decreased in the biofilm cell subpopulation. Three transcriptional factors were found to be increased or decreased among both cell subpopulations, suggesting their potential involvement in the regulation of these processes. Although no significant differences were observed for the known proteins related to ferrous iron and sulfur oxidation pathways among both cell subpopulations, the results presented here show that the early steps of At. ferrooxidans biofilm formation consist of a set of metabolic adaptations following cell attachment to the mineral surface. Functions such as extracellular polymeric substances biosynthesis seem to be pivotal. This first high-throughput proteomic study may also contribute to the annotation of several unknown At. ferrooxidans proteins found.
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Affiliation(s)
- Mario Vera
- Biofilm Centre, University of Duisburg-Essen, Duisburg-Essen, Germany
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155
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Nanda V, Hsieh D, Davis A. Prediction and design of outer membrane protein-protein interactions. Methods Mol Biol 2013; 1063:183-96. [PMID: 23975778 DOI: 10.1007/978-1-62703-583-5_10] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Protein-protein interactions (PPI) play central roles in biological processes, motivating us to understand the structural basis underlying affinity and specificity. In this chapter, we focus on biochemical and computational design strategies of assessing and detecting PPIs of β-barrel outer membrane proteins (OMPs). A few case studies are presented highlighting biochemical techniques used to dissect the energetics of oligomerization and determine amino acids forming the key interactions of the PPI sites. Current computational strategies for detecting/predicting PPIs are introduced, and examples of computational and rational engineering strategies applied to OMPs are presented.
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Affiliation(s)
- Vikas Nanda
- Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School-UMDNJ, Piscataway, NJ, USA
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156
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Ruiz N. A bird's eye view of the bacterial landscape. Methods Mol Biol 2013; 966:1-14. [PMID: 23299725 DOI: 10.1007/978-1-62703-245-2_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Bacteria interact with the environment through their cell surface. Activities as diverse as attaching to a catheter, crawling on a surface, swimming through a pond, or being preyed on by a bacteriophage depend on the composition and structure of the cell surface. The cell surface must also protect bacteria from harmful chemicals present in the environment while allowing the intake of nutrients and excretion of toxic molecules. Bacteria have evolved four main types of bacterial cell surfaces to accomplish these functions: those of the typical gram-negative and gram-positive bacteria, and those of the Actinobacteria and Mollicutes. So few types seems remarkable since bacteria are very diverse and abundant, and they can live in many different environments. However, each species has tweaked these stereotypical bacterial surfaces to best fit its needs. The result is an amazing diversity of the bacterial landscape, most of which remains unexplored. Here I give an overview of the main features of the bacterial cell surface and highlight how advances in methodology have moved forward this field of study.
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Affiliation(s)
- Natividad Ruiz
- Department of Microbiology, The Ohio State University, Columbus, OH, USA.
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157
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Grangeasse C, Nessler S, Mijakovic I. Bacterial tyrosine kinases: evolution, biological function and structural insights. Philos Trans R Soc Lond B Biol Sci 2012; 367:2640-55. [PMID: 22889913 DOI: 10.1098/rstb.2011.0424] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Reversible protein phosphorylation is a major mechanism in the regulation of fundamental signalling events in all living organisms. Bacteria have been shown to possess a versatile repertoire of protein kinases, including histidine and aspartic acid kinases, serine/threonine kinases, and more recently tyrosine and arginine kinases. Tyrosine phosphorylation is today recognized as a key regulatory device of bacterial physiology, linked to exopolysaccharide production, virulence, stress response and DNA metabolism. However, bacteria have evolved tyrosine kinases that share no resemblance with their eukaryotic counterparts and are unique in exploiting the ATP/GTP-binding Walker motif to catalyse autophosphorylation and substrate phosphorylation on tyrosine. These enzymes, named BY-kinases (for Bacterial tYrosine kinases), have been identified in a majority of sequenced bacterial genomes, and to date no orthologues have been found in Eukarya. The aim of this review was to present the most recent knowledge about BY-kinases by focusing primarily on their evolutionary origin, structural and functional aspects, and emerging regulatory potential based on recent bacterial phosphoproteomic studies.
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Affiliation(s)
- Christophe Grangeasse
- Bases Moléculaires et Structurales des Systèmes Infectieux, IBCP, CNRS, Université de Lyon, UMR 5086, 7 passage du Vercors, 69367 Lyon, France.
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158
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Lin TL, Yang FL, Yang AS, Peng HP, Li TL, Tsai MD, Wu SH, Wang JT. Amino acid substitutions of MagA in Klebsiella pneumoniae affect the biosynthesis of the capsular polysaccharide. PLoS One 2012; 7:e46783. [PMID: 23118860 PMCID: PMC3485256 DOI: 10.1371/journal.pone.0046783] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2012] [Accepted: 09/06/2012] [Indexed: 11/18/2022] Open
Abstract
Mucoviscosity-associated gene A (magA) of Klebsiella pneumoniae contributes to K1 capsular polysaccharide (CPS) biosynthesis. Based on sequence homology and gene alignment, the magA gene has been predicted to encode a Wzy-type CPS polymerase. Sequence alignment with the Wzy_C and RfaL protein families (which catalyze CPS or lipopolysaccharide (LPS) biosynthesis) and topological analysis has suggested that eight highly conserved residues, including G308, G310, G334, G337, R290, P305, H323, and N324, were located in a hypothetical loop region. Therefore, we used site-directed mutagenesis to study the role of these residues in CPS production, and to observe the consequent phenotypes such as mucoviscosity, serum and phagocytosis resistance, and virulence (as assessed in mice) in pyogenic liver abscess strain NTUH-K2044. Alanine substitutions at R290 or H323 abolished all of these properties. The G308A mutant was severely impaired for these functions. The G334A mutant remained mucoid with decreased CPS production, but its virulence was significantly reduced in vivo. No phenotypic change was observed for strains harboring magA G310A, G337A, P305A, or N324A mutations. Therefore, R290, G308, H323, and G334 are functionally important residues of the MagA (Wzy) protein of K. pneumoniae NTUH-K2044, capsular type K1. These amino acids are also likely to be important for the function of Wzy in other capsular types in K. pneumoniae and other species bearing Wzy_C family proteins.
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Affiliation(s)
- Tzu-Lung Lin
- Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan
| | - Feng-Ling Yang
- Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
| | - An-Suei Yang
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
| | - Hung-Pin Peng
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
| | - Tsung-Lin Li
- Genomics Research Center, Academia Sinica, Taipei, Taiwan
| | - Ming-Daw Tsai
- Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
- * E-mail: (MDT); (SHW); (JTW)
| | - Shih-Hsiung Wu
- Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
- * E-mail: (MDT); (SHW); (JTW)
| | - Jin-Town Wang
- Department of Microbiology, National Taiwan University College of Medicine, Taipei, Taiwan
- Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
- * E-mail: (MDT); (SHW); (JTW)
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159
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Whitney JC, Howell PL. Synthase-dependent exopolysaccharide secretion in Gram-negative bacteria. Trends Microbiol 2012; 21:63-72. [PMID: 23117123 DOI: 10.1016/j.tim.2012.10.001] [Citation(s) in RCA: 154] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2012] [Revised: 09/28/2012] [Accepted: 10/03/2012] [Indexed: 01/26/2023]
Abstract
The biosynthesis and export of bacterial cell-surface polysaccharides is known to occur through several distinct mechanisms. Recent advances in the biochemistry and structural biology of several proteins in synthase-dependent polysaccharide secretion systems have identified key conserved components of this pathway in Gram-negative bacteria. These components include an inner-membrane-embedded polysaccharide synthase, a periplasmic tetratricopeptide repeat (TPR)-containing scaffold protein, and an outer-membrane β-barrel porin. There is also increasing evidence that many synthase-dependent systems are post-translationally regulated by the bacterial second messenger bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP). Here, we compare these core proteins in the context of the alginate, cellulose, and poly-β-D-N-acetylglucosamine (PNAG) secretion systems.
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Affiliation(s)
- J C Whitney
- Program in Molecular Structure and Function, The Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada
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160
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Galván EM, Ielmini MV, Patel YN, Bianco MI, Franceschini EA, Schneider JC, Ielpi L. Xanthan chain length is modulated by increasing the availability of the polysaccharide copolymerase protein GumC and the outer membrane polysaccharide export protein GumB. Glycobiology 2012; 23:259-72. [DOI: 10.1093/glycob/cws146] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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161
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Jacobs M, Salinas SR, Bianco MI, Ielpi L. Expression, purification and crystallization of the outer membrane lipoprotein GumB from Xanthomonas campestris. Acta Crystallogr Sect F Struct Biol Cryst Commun 2012; 68:1255-8. [PMID: 23027761 PMCID: PMC3497991 DOI: 10.1107/s1744309112036597] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 08/22/2012] [Indexed: 01/28/2023]
Abstract
GumB is a predicted outer membrane lipoprotein that is involved in the synthesis and/or secretion of xanthan gum. This exopolysaccharide, produced by Xanthomonas campestris, is valuable in industry because of its important rheological properties. Solution of the GumB structure will provide insight into the polymerization and/or secretion mechanisms of xanthan gum. GumB was overexpressed and purified and diffraction-quality crystals of native GumB were obtained. A complete data set was collected to 2.54 Å resolution with an R(p.i.m.) of 0.034. The crystals belonged to space group P2(1)2(1)2(1), with unit-cell parameters a = 84.4, b = 90.5, c = 120.7 Å.
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Affiliation(s)
- Melisa Jacobs
- Laboratory of Bacterial Genetics, Fundación Instituto Leloir, IIBBA–CONICET, Avenida Patricias Argentinas 435, C1405BWE Buenos Aires, Argentina
| | - Silvina R. Salinas
- Laboratory of Bacterial Genetics, Fundación Instituto Leloir, IIBBA–CONICET, Avenida Patricias Argentinas 435, C1405BWE Buenos Aires, Argentina
| | - María I. Bianco
- Laboratory of Bacterial Genetics, Fundación Instituto Leloir, IIBBA–CONICET, Avenida Patricias Argentinas 435, C1405BWE Buenos Aires, Argentina
| | - Luis Ielpi
- Laboratory of Bacterial Genetics, Fundación Instituto Leloir, IIBBA–CONICET, Avenida Patricias Argentinas 435, C1405BWE Buenos Aires, Argentina
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162
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Molecular characterization of the viaB locus encoding the biosynthetic machinery for Vi capsule formation in Salmonella Typhi. PLoS One 2012; 7:e45609. [PMID: 23029132 PMCID: PMC3448643 DOI: 10.1371/journal.pone.0045609] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2012] [Accepted: 08/23/2012] [Indexed: 01/30/2023] Open
Abstract
The Vi capsular polysaccharide (CPS) of Salmonella enterica serovar Typhi, the cause of human typhoid, is important for infectivity and virulence. The Vi biosynthetic machinery is encoded within the viaB locus composed of 10 genes involved in regulation of expression (tviA), polymer synthesis (tviB-tviE), and cell surface localization of the CPS (vexA-vexE). We cloned the viaB locus from S. Typhi and transposon insertion mutants of individual viaB genes were characterized in Escherichia coli DH5α. Phenotype analysis of viaB mutants revealed that tviB, tviC, tviD and tviE are involved in Vi polymer synthesis. Furthermore, expression of tviB-tviE in E. coli DH5α directed the synthesis of cytoplasmic Vi antigen. Mutants of the ABC transporter genes vexBC and the polysaccharide copolymerase gene vexD accumulated the Vi polymer within the cytoplasm and productivity in these mutants was greatly reduced. In contrast, de novo synthesis of Vi polymer in the export deficient vexA mutant was comparable to wild-type cells, with drastic effects on cell stability. VexE mutant cells exported the Vi, but the CPS was not retained at the cell surface. The secreted polymer of a vexE mutant had different physical characteristics compared to the wild-type Vi.
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163
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SurA is involved in the targeting to the outer membrane of a Tat signal sequence-anchored protein. J Bacteriol 2012; 194:6131-42. [PMID: 22961852 DOI: 10.1128/jb.01419-12] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The twin arginine translocation (Tat) pathway exports folded proteins from the cytoplasm to the periplasm of bacteria. The targeting of the exported proteins to the Tat pathway relies on a specific amino-terminal signal sequence, which is cleaved after exportation. In the phytopathogen Dickeya dadantii, the pectin lyase homologue PnlH is exported by the Tat pathway without cleavage of its signal sequence, which anchors PnlH into the outer membrane. In proteobacteria, the vast majority of outer membrane proteins consists of β-barrel proteins and lipoproteins. Thus, PnlH represents a new kind of outer membrane protein. In Escherichia coli, periplasmic chaperones SurA, Skp, and DegP work together with the β-barrel assembly machinery (Bam) to target and insert β-barrel proteins into the outer membrane. In this work, we showed that SurA is required for an efficient targeting of PnlH to the outer membrane. Moreover, we were able to detect an in vitro interaction between SurA and the PnlH signal sequence. Since the PnlH signal sequence contains a highly hydrophobic region, we propose that SurA protects it from the hydrophobic periplasm during targeting of PnlH to the outer membrane. We also studied the nature of the information carried by the PnlH signal sequence responsible for its targeting to the outer membrane after exportation by the Tat system.
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164
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Berry JL, Phelan MM, Collins RF, Adomavicius T, Tønjum T, Frye SA, Bird L, Owens R, Ford RC, Lian LY, Derrick JP. Structure and assembly of a trans-periplasmic channel for type IV pili in Neisseria meningitidis. PLoS Pathog 2012; 8:e1002923. [PMID: 23028322 PMCID: PMC3441751 DOI: 10.1371/journal.ppat.1002923] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2012] [Accepted: 08/07/2012] [Indexed: 01/24/2023] Open
Abstract
Type IV pili are polymeric fibers which protrude from the cell surface and play a critical role in adhesion and invasion by pathogenic bacteria. The secretion of pili across the periplasm and outer membrane is mediated by a specialized secretin protein, PilQ, but the way in which this large channel is formed is unknown. Using NMR, we derived the structures of the periplasmic domains from N. meningitidis PilQ: the N-terminus is shown to consist of two β-domains, which are unique to the type IV pilus-dependent secretins. The structure of the second β-domain revealed an eight-stranded β-sandwich structure which is a novel variant of the HSP20-like fold. The central part of PilQ consists of two α/β fold domains: the structure of the first of these is similar to domains from other secretins, but with an additional α-helix which links it to the second α/β domain. We also determined the structure of the entire PilQ dodecamer by cryoelectron microscopy: it forms a cage-like structure, enclosing a cavity which is approximately 55 Å in internal diameter at its largest extent. Specific regions were identified in the density map which corresponded to the individual PilQ domains: this allowed us to dock them into the cryoelectron microscopy density map, and hence reconstruct the entire PilQ assembly which spans the periplasm. We also show that the C-terminal domain from the lipoprotein PilP, which is essential for pilus assembly, binds specifically to the first α/β domain in PilQ and use NMR chemical shift mapping to generate a model for the PilP:PilQ complex. We conclude that passage of the pilus fiber requires disassembly of both the membrane-spanning and the β-domain regions in PilQ, and that PilP plays an important role in stabilising the PilQ assembly during secretion, through its anchorage in the inner membrane.
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Affiliation(s)
- Jamie-Lee Berry
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Marie M. Phelan
- Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Richard F. Collins
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Tomas Adomavicius
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Tone Tønjum
- Centre for Molecular Biology and Neuroscience, University of Oslo, Oslo, Norway
| | - Stefan A. Frye
- Centre for Molecular Biology and Neuroscience, University of Oslo, Oslo, Norway
| | - Louise Bird
- Oxford Protein Production Facility, Research Complex at Harwell, Harwell, Oxford, United Kingdom
| | - Ray Owens
- Oxford Protein Production Facility, Research Complex at Harwell, Harwell, Oxford, United Kingdom
| | - Robert C. Ford
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
| | - Lu-Yun Lian
- Institute of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Jeremy P. Derrick
- Faculty of Life Sciences, Michael Smith Building, University of Manchester, Manchester, United Kingdom
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165
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New currency for old rope: from coiled-coil assemblies to α-helical barrels. Curr Opin Struct Biol 2012; 22:432-41. [DOI: 10.1016/j.sbi.2012.03.002] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Revised: 03/01/2012] [Accepted: 03/01/2012] [Indexed: 11/18/2022]
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166
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Del Val C, White SH, Bondar AN. Ser/Thr motifs in transmembrane proteins: conservation patterns and effects on local protein structure and dynamics. J Membr Biol 2012; 245:717-30. [PMID: 22836667 DOI: 10.1007/s00232-012-9452-4] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2012] [Accepted: 06/04/2012] [Indexed: 01/16/2023]
Abstract
We combined systematic bioinformatics analyses and molecular dynamics simulations to assess the conservation patterns of Ser and Thr motifs in membrane proteins, and the effect of such motifs on the structure and dynamics of α-helical transmembrane (TM) segments. We find that Ser/Thr motifs are often present in β-barrel TM proteins. At least one Ser/Thr motif is present in almost half of the sequences of α-helical proteins analyzed here. The extensive bioinformatics analyses and inspection of protein structures led to the identification of molecular transporters with noticeable numbers of Ser/Thr motifs within the TM region. Given the energetic penalty for burying multiple Ser/Thr groups in the membrane hydrophobic core, the observation of transporters with multiple membrane-embedded Ser/Thr is intriguing and raises the question of how the presence of multiple Ser/Thr affects protein local structure and dynamics. Molecular dynamics simulations of four different Ser-containing model TM peptides indicate that backbone hydrogen bonding of membrane-buried Ser/Thr hydroxyl groups can significantly change the local structure and dynamics of the helix. Ser groups located close to the membrane interface can hydrogen bond to solvent water instead of protein backbone, leading to an enhanced local solvation of the peptide.
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Affiliation(s)
- Coral Del Val
- Department of Computer Science and Artificial Intelligence, University of Granada, Granada, Spain.
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167
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Jiang K, Sanseverino J, Chauhan A, Lucas S, Copeland A, Lapidus A, Del Rio TG, Dalin E, Tice H, Bruce D, Goodwin L, Pitluck S, Sims D, Brettin T, Detter JC, Han C, Chang YJ, Larimer F, Land M, Hauser L, Kyrpides NC, Mikhailova N, Moser S, Jegier P, Close D, Debruyn JM, Wang Y, Layton AC, Allen MS, Sayler GS. Complete genome sequence of Thauera aminoaromatica strain MZ1T. Stand Genomic Sci 2012; 6:325-35. [PMID: 23407619 PMCID: PMC3558969 DOI: 10.4056/sigs.2696029] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Thauera aminoaromatica strain MZ1T, an isolate belonging to genus Thauera, of the family Rhodocyclaceae and the class the Betaproteobacteria, has been characterized for its ability to produce abundant exopolysaccharide and degrade various aromatic compounds with nitrate as an electron acceptor. These properties, if fully understood at the genome-sequence level, can aid in environmental processing of organic matter in anaerobic cycles by short-circuiting a central anaerobic metabolite, acetate, from microbiological conversion to methane, a critical greenhouse gas. Strain MZ1T is the first strain from the genus Thauera with a completely sequenced genome. The 4,496,212 bp chromosome and 78,374 bp plasmid contain 4,071 protein-coding and 71 RNA genes, and were sequenced as part of the DOE Community Sequencing Program CSP_776774.
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Affiliation(s)
- Ke Jiang
- Center for Environmental Biotechnology, The University of Tennessee, Knoxville, Tennessee, USA
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168
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Prehna G, Zhang G, Gong X, Duszyk M, Okon M, McIntosh L, Weiner J, Strynadka N. A Protein Export Pathway Involving Escherichia coli Porins. Structure 2012; 20:1154-66. [DOI: 10.1016/j.str.2012.04.014] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2011] [Revised: 04/16/2012] [Accepted: 04/16/2012] [Indexed: 11/28/2022]
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169
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Douzi B, Filloux A, Voulhoux R. On the path to uncover the bacterial type II secretion system. Philos Trans R Soc Lond B Biol Sci 2012; 367:1059-72. [PMID: 22411978 DOI: 10.1098/rstb.2011.0204] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Gram-negative bacteria have evolved several secretory pathways to release enzymes or toxins into the surrounding environment or into the target cells. The type II secretion system (T2SS) is conserved in Gram-negative bacteria and involves a set of 12 to 16 different proteins. Components of the T2SS are located in both the inner and outer membranes where they assemble into a supramolecular complex spanning the bacterial envelope, also called the secreton. The T2SS substrates transiently go through the periplasm before they are translocated across the outer membrane and exposed to the extracellular milieu. The T2SS is unique in its ability to promote secretion of large and sometimes multimeric proteins that are folded in the periplasm. The present review describes recently identified protein-protein interactions together with structural and functional advances in the field that have contributed to improve our understanding on how the type II secretion apparatus assembles and on the role played by individual proteins of this highly sophisticated system.
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Affiliation(s)
- Badreddine Douzi
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (CNRS-LISM-UPR 9027), Aix-Marseille Universités, Institut de Microbiologie de la Méditerranée, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France
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170
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Crystal structure of the enzyme CapF of Staphylococcus aureus reveals a unique architecture composed of two functional domains. Biochem J 2012; 443:671-80. [PMID: 22320426 DOI: 10.1042/bj20112049] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
CP (capsular polysaccharide) is an important virulence factor during infections by the bacterium Staphylococcus aureus. The enzyme CapF is an attractive therapeutic candidate belonging to the biosynthetic route of CP of pathogenic strains of S. aureus. In the present study, we report two independent crystal structures of CapF in an open form of the apoenzyme. CapF is a homodimer displaying a characteristic dumb-bell-shaped architecture composed of two domains. The N-terminal domain (residues 1-252) adopts a Rossmann fold belonging to the short-chain dehydrogenase/reductase family of proteins. The C-terminal domain (residues 252-369) displays a standard cupin fold with a Zn2+ ion bound deep in the binding pocket of the β-barrel. Functional and thermodynamic analyses indicated that each domain catalyses separate enzymatic reactions. The cupin domain is necessary for the C3-epimerization of UDP-4-hexulose. Meanwhile, the N-terminal domain catalyses the NADPH-dependent reduction of the intermediate species generated by the cupin domain. Analysis by ITC (isothermal titration calorimetry) revealed a fascinating thermodynamic switch governing the attachment and release of the coenzyme NADPH during each catalytic cycle. These observations suggested that the binding of coenzyme to CapF facilitates a disorder-to-order transition in the catalytic loop of the reductase (N-terminal) domain. We anticipate that the present study will improve the general understanding of the synthesis of CP in S. aureus and will aid in the design of new therapeutic agents against this pathogenic bacterium.
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171
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Dynamic association of BAM complex modules includes surface exposure of the lipoprotein BamC. J Mol Biol 2012; 422:545-55. [PMID: 22683355 DOI: 10.1016/j.jmb.2012.05.035] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2012] [Revised: 05/09/2012] [Accepted: 05/30/2012] [Indexed: 11/21/2022]
Abstract
The β-barrel assembly machinery (BAM) complex drives the assembly of β-barrel proteins into the outer membrane of gram-negative bacteria. It is composed of five subunits: BamA, BamB, BamC, BamD, and BamE. We find that the BAM complex isolated from the outer membrane of Escherichia coli consists of a core complex of BamA:B:C:D:E and, in addition, a BamA:B module and a BamC:D module. In the absence of BamC, these modules are destabilized, resulting in increased protease susceptibility of BamD and BamB. While the N-terminus of BamC carries a highly conserved region crucial for stable interaction with BamD, immunofluorescence, immunoprecipitation, and protease-sensitivity assays show that the C-terminal domain of BamC, composed of two helix-grip motifs, is exposed on the surface of E. coli. This unexpected topology of a bacterial lipoprotein is reminiscent of the analogous protein subunits from the mitochondrial β-barrel insertion machinery, the SAM complex. The modular arrangement and topological features provide new insight into the architecture of the BAM complex, towards a better understanding of the mechanism driving β-barrel membrane protein assembly.
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172
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Wet-surface-enhanced ellipsometric contrast microscopy identifies slime as a major adhesion factor during bacterial surface motility. Proc Natl Acad Sci U S A 2012; 109:10036-41. [PMID: 22665761 DOI: 10.1073/pnas.1120979109] [Citation(s) in RCA: 68] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
In biology, the extracellular matrix (ECM) promotes both cell adhesion and specific recognition, which is essential for central developmental processes in both eukaryotes and prokaryotes. However, live studies of the dynamic interactions between cells and the ECM, for example during motility, have been greatly impaired by imaging limitations: mostly the ability to observe the ECM at high resolution in absence of specific staining by live microscopy. To solve this problem, we developed a unique technique, wet-surface enhanced ellipsometry contrast (Wet-SEEC), which magnifies the contrast of transparent organic materials deposited on a substrate (called Wet-surf) with exquisite sensitivity. We show that Wet-SEEC allows both the observation of unprocessed nanofilms as low as 0.2 nm thick and their accurate 3D topographic reconstructions, directly by standard light microscopy. We next used Wet-SEEC to image slime secretion, a poorly defined property of many prokaryotic and eukaryotic organisms that move across solid surfaces in absence of obvious extracellular appendages (gliding). Using combined Wet-SEEC and fluorescent-staining experiments, we observed slime deposition by gliding Myxococcus xanthus cells at unprecedented resolution. Altogether, the results revealed that in this bacterium, slime associates preferentially with the outermost components of the motility machinery and promotes its adhesion to the substrate on the ventral side of the cell. Strikingly, analogous roles have been proposed for the extracellular proteoglycans of gliding diatoms and apicomplexa, suggesting that slime deposition is a general means for gliding organisms to adhere and move over surfaces.
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173
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Hagelueken G, Ward R, Naismith JH, Schiemann O. MtsslWizard: In Silico Spin-Labeling and Generation of Distance Distributions in PyMOL. APPLIED MAGNETIC RESONANCE 2012; 42:377-391. [PMID: 22448103 PMCID: PMC3296949 DOI: 10.1007/s00723-012-0314-0] [Citation(s) in RCA: 171] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Indexed: 05/09/2023]
Abstract
MtsslWizard is a computer program, which operates as a plugin for the PyMOL molecular graphics system. MtsslWizard estimates distances between spin labels on proteins quickly with user-configurable options through a simple graphical interface. In default mode, the program searches for ensembles of possible MTSSL conformations that do not clash with a static model of the protein. Once conformations are assigned, distance distributions between two or more ensembles are calculated, displayed, and can be exported to other software. The program's use is evaluated in a number of challenging test cases and its strengths and weaknesses evaluated. The benefits of the program are its accuracy and simplicity. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00723-012-0314-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Gregor Hagelueken
- Biomedical Sciences Research Complex, The University of St. Andrews, Fife, KY16 9ST UK
| | - Richard Ward
- Biomedical Sciences Research Complex, The University of St. Andrews, Fife, KY16 9ST UK
| | - James H. Naismith
- Biomedical Sciences Research Complex, The University of St. Andrews, Fife, KY16 9ST UK
| | - Olav Schiemann
- Biomedical Sciences Research Complex, The University of St. Andrews, Fife, KY16 9ST UK
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174
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Kalynych S, Yao D, Magee J, Cygler M. Structural characterization of closely related O-antigen lipopolysaccharide (LPS) chain length regulators. J Biol Chem 2012; 287:15696-705. [PMID: 22437828 DOI: 10.1074/jbc.m112.354837] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The surface O-antigen polymers of gram-negative bacteria exhibit a modal length distribution that depends on dedicated chain length regulator periplasmic proteins (polysaccharide co-polymerases, PCPs) anchored in the inner membrane by two transmembrane helices. In an attempt to determine whether structural changes underlie the O-antigen modal length specification, we have determined the crystal structures of several closely related PCPs, namely two chimeric PCP-1 family members solved at 1.6 and 2.8 Å and a wild-type PCP-1 from Shigella flexneri solved at 2.8 Å. The chimeric proteins form circular octamers, whereas the wild-type WzzB from S. flexneri was found to be an open trimer. We also present the structure of a Wzz(FepE) mutant, which exhibits severe attenuation in its ability to produce very long O-antigen polymers. Our findings suggest that the differences in the modal length distribution depend primarily on the surface-exposed amino acids in specific regions rather than on the differences in the oligomeric state of the PCP protomers.
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Affiliation(s)
- Sergei Kalynych
- Department of Biochemistry, McGill University, Montreal, Quebec H3G 0B1, Canada
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175
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Ferreira AS, Silva IN, Oliveira VH, Cunha R, Moreira LM. Insights into the role of extracellular polysaccharides in Burkholderia adaptation to different environments. Front Cell Infect Microbiol 2011; 1:16. [PMID: 22919582 PMCID: PMC3417362 DOI: 10.3389/fcimb.2011.00016] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2011] [Accepted: 11/21/2011] [Indexed: 12/11/2022] Open
Abstract
The genus Burkholderia comprises more than 60 species able to adapt to a wide range of environments such as soil and water, and also colonize and infect plants and animals. They have large genomes with multiple replicons and high gene number, allowing these bacteria to thrive in very different niches. Among the properties of bacteria from the genus Burkholderia is the ability to produce several types of exopolysaccharides (EPSs). The most common one, cepacian, is produced by the majority of the strains examined irrespective of whether or not they belong to the Burkholderia cepacia complex (Bcc). Cepacian biosynthesis proceeds by a Wzy-dependent mechanism, and some of the B. cepacia exopolysaccharide (Bce) proteins have been functionally characterized. In vitro studies showed that cepacian protects bacterial cells challenged with external stresses. Regarding virulence, bacterial cells with the ability to produce EPS are more virulent in several animal models of infection than their isogenic non-producing mutants. Although the production of EPS within the lungs of cystic fibrosis (CF) patients has not been demonstrated, the in vitro assessment of the mucoid phenotype in serial Bcc isolates from CF patients colonized for several years showed that mucoid to non-mucoid transitions are relatively frequent. This morphotype variation can be induced under laboratory conditions by exposing cells to stress such as high antibiotic concentration. Clonal isolates where mucoid to non-mucoid transition had occurred showed that during lung infection, genomic rearrangements, and mutations had taken place. Other phenotypic changes include variations in motility, chemotaxis, biofilm formation, bacterial survival rate under nutrient starvation and virulence. In this review, we summarize major findings related to EPS biosynthesis by Burkholderia and the implications in broader regulatory mechanisms important for cell adaptation to the different niches colonized by these bacteria.
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Affiliation(s)
- Ana S Ferreira
- Institute for Biotechnology and Bioengineering, Centre for Biological and Chemical Engineering, Instituto Superior Técnico Lisboa, Portugal
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176
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Zaccai NR, Chi B, Thomson AR, Boyle AL, Bartlett GJ, Bruning M, Linden N, Sessions RB, Booth PJ, Brady RL, Woolfson DN. A de novo peptide hexamer with a mutable channel. Nat Chem Biol 2011; 7:935-41. [PMID: 22037471 PMCID: PMC3223406 DOI: 10.1038/nchembio.692] [Citation(s) in RCA: 149] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Accepted: 08/19/2011] [Indexed: 11/10/2022]
Abstract
The design of new proteins that expand the repertoire of natural protein structures represents a formidable challenge. Success in this area would increase understanding of protein structure, and present new scaffolds that could be exploited in biotechnology and synthetic biology. Here we describe the design, characterisation and X-ray crystal structure of a new coiled-coil protein. The de novo sequence forms a stand-alone, parallel, 6-helix bundle with a channel running through it. Although lined exclusively by hydrophobic leucine and isoleucine side chains, the 6 Å channel is permeable to water. One layer of leucine residues within the channel is mutable accepting polar aspartic acid (Asp) and histidine (His) side chains, and leading to subdivision and organization of solvent within the lumen. Moreover, these mutants can be combined to form a stable and unique (Asp-His)3 heterohexamer. These new structures provide a basis for engineering de novo proteins with new functions.
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177
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Marassi FM. Mycobacterium tuberculosis Rv0899 defines a family of membrane proteins widespread in nitrogen-fixing bacteria. Proteins 2011; 79:2946-55. [PMID: 21905117 DOI: 10.1002/prot.23151] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 06/30/2011] [Accepted: 07/21/2011] [Indexed: 11/07/2022]
Abstract
The Mycobacterium tuberculosis membrane protein Rv0899 confers adaptation of the bacterium to acidic environments. Due to strong sequence homology of its C-terminus to bacterial OmpA-like domains, Rv0899 has been proposed to constitute an outer membrane porin of M. tuberculosis. However, OmpA-like domains are widespread in a wide variety of bacterial proteins with different functions. Furthermore, the three-dimensional structure of Rv0899 does not contain a transmembrane β-barrel, and recent evidence demonstrates that it does not have porin activity. Instead, the rv0899 gene is part of an operon (rv0899-rv0901) that is required for fast ammonia secretion, pH neutralization, and growth of M. tuberculosis in acidic environments. The mechanism whereby these functions are accomplished is not known. To gain further functional insights, a targeted search of the genomic databases was performed for proteins with sequence similarity beyond the OmpA-like C-terminus. The results presented here, show that Rv0899-like proteins are widespread in bacteria with functions in nitrogen metabolism, adaptation to nutrient poor environments, and/or establishing symbiosis with the host organism, and appear to form a protein family. These findings suggest that M. tuberculosis Rv0899 may also assist similar processes and lend further support to its role in ammonia secretion and M. tuberculosis adaptation to the host environment.
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Affiliation(s)
- Francesca M Marassi
- Sanford Burnham Medical Research Institute, La Jolla, California 92037, USA.
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178
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Franklin MJ, Nivens DE, Weadge JT, Howell PL. Biosynthesis of the Pseudomonas aeruginosa Extracellular Polysaccharides, Alginate, Pel, and Psl. Front Microbiol 2011; 2:167. [PMID: 21991261 PMCID: PMC3159412 DOI: 10.3389/fmicb.2011.00167] [Citation(s) in RCA: 338] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Accepted: 07/19/2011] [Indexed: 12/30/2022] Open
Abstract
Pseudomonas aeruginosa thrives in many aqueous environments and is an opportunistic pathogen that can cause both acute and chronic infections. Environmental conditions and host defenses cause differing stresses on the bacteria, and to survive in vastly different environments, P. aeruginosa must be able to adapt to its surroundings. One strategy for bacterial adaptation is to self-encapsulate with matrix material, primarily composed of secreted extracellular polysaccharides. P. aeruginosa has the genetic capacity to produce at least three secreted polysaccharides; alginate, Psl, and Pel. These polysaccharides differ in chemical structure and in their biosynthetic mechanisms. Since alginate is often associated with chronic pulmonary infections, its biosynthetic pathway is the best characterized. However, alginate is only produced by a subset of P. aeruginosa strains. Most environmental and other clinical isolates secrete either Pel or Psl. Little information is available on the biosynthesis of these polysaccharides. Here, we review the literature on the alginate biosynthetic pathway, with emphasis on recent findings describing the structure of alginate biosynthetic proteins. This information combined with the characterization of the domain architecture of proteins encoded on the Psl and Pel operons allowed us to make predictive models for the biosynthesis of these two polysaccharides. The results indicate that alginate and Pel share certain features, including some biosynthetic proteins with structurally or functionally similar properties. In contrast, Psl biosynthesis resembles the EPS/CPS capsular biosynthesis pathway of Escherichia coli, where the Psl pentameric subunits are assembled in association with an isoprenoid lipid carrier. These models and the environmental cues that cause the cells to produce predominantly one polysaccharide over the others are subjects of current investigation.
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179
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Structural basis for alginate secretion across the bacterial outer membrane. Proc Natl Acad Sci U S A 2011; 108:13083-8. [PMID: 21778407 DOI: 10.1073/pnas.1104984108] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pseudomonas aeruginosa is the predominant pathogen associated with chronic lung infection among cystic fibrosis patients. During colonization of the lung, P. aeruginosa converts to a mucoid phenotype characterized by the overproduction of the exopolysaccharide alginate. Secretion of newly synthesized alginate across the outer membrane is believed to occur through the outer membrane protein AlgE. Here we report the 2.3 Å crystal structure of AlgE, which reveals a monomeric 18-stranded β-barrel characterized by a highly electropositive pore constriction formed by an arginine-rich conduit that likely acts as a selectivity filter for the negatively charged alginate polymer. Interestingly, the pore constriction is occluded on either side by extracellular loop L2 and an unusually long periplasmic loop, T8. In halide efflux assays, deletion of loop T8 (ΔT8-AlgE) resulted in a threefold increase in anion flux compared to the wild-type or ΔL2-AlgE supporting the idea that AlgE forms a transport pathway through the membrane and suggesting that transport is regulated by T8. This model is further supported by in vivo experiments showing that complementation of an algE deletion mutant with ΔT8-AlgE impairs alginate production. Taken together, these studies support a mechanism for exopolysaccharide export across the outer membrane that is distinct from the Wza-mediated translocation observed in canonical capsular polysaccharide export systems.
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180
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Filloux A. Protein Secretion Systems in Pseudomonas aeruginosa: An Essay on Diversity, Evolution, and Function. Front Microbiol 2011; 2:155. [PMID: 21811488 PMCID: PMC3140646 DOI: 10.3389/fmicb.2011.00155] [Citation(s) in RCA: 122] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Accepted: 07/01/2011] [Indexed: 12/25/2022] Open
Abstract
Protein secretion systems are molecular nanomachines used by Gram-negative bacteria to thrive within their environment. They are used to release enzymes that hydrolyze complex carbon sources into usable compounds, or to release proteins that capture essential ions such as iron. They are also used to colonize and survive within eukaryotic hosts, causing acute or chronic infections, subverting the host cell response and escaping the immune system. In this article, the opportunistic human pathogen Pseudomonas aeruginosa is used as a model to review the diversity of secretion systems that bacteria have evolved to achieve these goals. This diversity may result from a progressive transformation of cell envelope complexes that initially may not have been dedicated to secretion. The striking similarities between secretion systems and type IV pili, flagella, bacteriophage tail, or efflux pumps is a nice illustration of this evolution. Differences are also needed since various secretion configurations call for diversity. For example, some proteins are released in the extracellular medium while others are directly injected into the cytosol of eukaryotic cells. Some proteins are folded before being released and transit into the periplasm. Other proteins cross the whole cell envelope at once in an unfolded state. However, the secretion system requires conserved basic elements or features. For example, there is a need for an energy source or for an outer membrane channel. The structure of this review is thus quite unconventional. Instead of listing secretion types one after each other, it presents a melting pot of concepts indicating that secretion types are in constant evolution and use basic principles. In other words, emergence of new secretion systems could be predicted the way Mendeleïev had anticipated characteristics of yet unknown elements.
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Affiliation(s)
- Alain Filloux
- Division of Cell and Molecular Biology, Centre for Molecular Microbiology and Infection, Imperial College London London, UK
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181
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Structural insights into the oligomerization and architecture of eukaryotic membrane pore-forming toxins. Structure 2011; 19:181-91. [PMID: 21300287 DOI: 10.1016/j.str.2010.11.013] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2010] [Revised: 11/01/2010] [Accepted: 11/06/2010] [Indexed: 01/27/2023]
Abstract
Pore-forming toxins (PFTs) are proteins that are secreted as soluble molecules and are inserted into membranes to form oligomeric transmembrane pores. In this paper, we report the crystal structure of Fragaceatoxin C (FraC), a PFT isolated from the sea anemone Actinia fragacea, at 1.8 Å resolution. It consists of a crown-shaped nonamer with an external diameter of about 11.0 nm and an internal diameter of approximately 5.0 nm. Cryoelectron microscopy studies of FraC in lipid bilayers reveal the pore structure that traverses the membrane. The shape and dimensions of the crystallographic oligomer are fully consistent with the membrane pore. The FraC structure provides insight into the interactions governing the assembly process and suggests the structural changes that allow for membrane insertion. We propose a nonameric pore model that spans the membrane by forming a lipid-free α-helical bundle pore.
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182
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How hydrophobic molecules traverse the outer membranes of gram-negative bacteria. Proc Natl Acad Sci U S A 2011; 108:10929-30. [PMID: 21693645 DOI: 10.1073/pnas.1106927108] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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183
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Sathiyamoorthy K, Mills E, Franzmann TM, Rosenshine I, Saper MA. The crystal structure of Escherichia coli group 4 capsule protein GfcC reveals a domain organization resembling that of Wza. Biochemistry 2011; 50:5465-76. [PMID: 21449614 DOI: 10.1021/bi101869h] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report the 1.9 Å resolution crystal structure of enteropathogenic Escherichia coli GfcC, a periplasmic protein encoded by the gfc operon, which is essential for assembly of group 4 polysaccharide capsule (O-antigen capsule). Presumed gene orthologs of gfcC are present in capsule-encoding regions of at least 29 genera of Gram-negative bacteria. GfcC, a member of the DUF1017 family, is comprised of tandem β-grasp (ubiquitin-like) domains (D2 and D3) and a carboxyl-terminal amphipathic helix, a domain arrangement reminiscent of that of Wza that forms an exit pore for group 1 capsule export. Unlike the membrane-spanning C-terminal helix from Wza, the GfcC C-terminal helix packs against D3. Previously unobserved in a β-grasp domain structure is a 48-residue helical hairpin insert in D2 that binds to D3, constraining its position and sequestering the carboxyl-terminal amphipathic helix. A centrally located and invariant Arg115 not only is essential for proper localization but also forms one of two mostly conserved pockets. Finally, we draw analogies between a GfcC protein fused to an outer membrane β-barrel pore in some species and fusion proteins necessary for secreting biofilm-forming exopolysaccharides.
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184
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Larue K, Ford RC, Willis LM, Whitfield C. Functional and structural characterization of polysaccharide co-polymerase proteins required for polymer export in ATP-binding cassette transporter-dependent capsule biosynthesis pathways. J Biol Chem 2011; 286:16658-68. [PMID: 21454677 PMCID: PMC3089508 DOI: 10.1074/jbc.m111.228221] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2011] [Revised: 03/17/2011] [Indexed: 11/06/2022] Open
Abstract
Neisseria meningitidis serogroup B and Escherichia coli K1 bacteria produce a capsular polysaccharide (CPS) that is composed of α2,8-linked polysialic acid (PSA). Biosynthesis of PSA in these bacteria occurs via an ABC (ATP-binding cassette) transporter-dependent pathway. In N. meningitidis, export of PSA to the surface of the bacterium requires two proteins that form an ABC transporter (CtrC and CtrD) and two additional proteins, CtrA and CtrB, that are proposed to form a cell envelope-spanning export complex. CtrA is a member of the outer membrane polysaccharide export (OPX) family of proteins, which are proposed to form a pore to mediate export of CPSs across the outer membrane. CtrB is an inner membrane protein belonging to the polysaccharide co-polymerase (PCP) family. PCP proteins involved in other bacterial polysaccharide assembly systems form structures that extend into the periplasm from the inner membrane. There is currently no structural information available for PCP or OPX proteins involved in an ABC transporter-dependent CPS biosynthesis pathway to support their proposed roles in polysaccharide export. Here, we report cryo-EM images of purified CtrB reconstituted into lipid bilayers. These images contained molecular top and side views of CtrB and showed that it formed a conical oligomer that extended ∼125 Å from the membrane. This structure is consistent with CtrB functioning as a component of an envelope-spanning complex. Cross-complementation of CtrA and CtrB in E. coli mutants with defects in genes encoding the corresponding PCP and OPX proteins show that PCP-OPX pairs require interactions with their cognate partners to export polysaccharide. These experiments add further support for the model of an ABC transporter-PCP-OPX multiprotein complex that functions to export CPS across the cell envelope.
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Affiliation(s)
- Kane Larue
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1 and
| | - Robert C. Ford
- the Faculty of Life Science, University of Manchester, Manchester M60 1QD, United Kingdom
| | - Lisa M. Willis
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1 and
| | - Chris Whitfield
- From the Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1 and
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185
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Schell MA, Zhao P, Wells L. Outer membrane proteome of Burkholderia pseudomallei and Burkholderia mallei from diverse growth conditions. J Proteome Res 2011; 10:2417-24. [PMID: 21391724 PMCID: PMC4917286 DOI: 10.1021/pr1012398] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Burkholderia mallei and Burkholderia pseudomallei are closely related, aerosol-infective human pathogens that cause life-threatening diseases. Biochemical analyses requiring large-scale growth and manipulation at biosafety level 3 under select agent regulations are cumbersome and hazardous. We developed a simple, safe, and rapid method to prepare highly purified outer membrane (OM) fragments from these pathogens. Shotgun proteomic analyses of OMs by trypsin shaving and mass spectrometry identified >155 proteins, the majority of which are clearly outer membrane proteins (OMPs). These included: 13 porins, 4 secretins for virulence factor export, 11 efflux pumps, multiple components of a Type VI secreton, metal transport receptors, polysaccharide exporters, and hypothetical OMPs of unknown function. We also identified 20 OMPs in each pathogen that are abundant under a wide variety of conditions, including in serum and with macrophages, suggesting these are fundamental for growth and survival and may represent prime drug or vaccine targets. Comparison of the OM proteomes of B. mallei and B. pseudomallei showed many similarities but also revealed a few differences, perhaps reflecting evolution of B. mallei away from environmental survival toward host-adaptation.
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Affiliation(s)
- Mark A Schell
- Department of Microbiology, University of Georgia, Athens, Georgia 30602, United States.
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186
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Bazaka K, Jacob MV, Crawford RJ, Ivanova EP. Plasma-assisted surface modification of organic biopolymers to prevent bacterial attachment. Acta Biomater 2011; 7:2015-28. [PMID: 21194574 DOI: 10.1016/j.actbio.2010.12.024] [Citation(s) in RCA: 220] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Revised: 12/01/2010] [Accepted: 12/20/2010] [Indexed: 12/30/2022]
Abstract
Despite many synthetic biomaterials having physical properties that are comparable or even superior to those of natural body tissues, they frequently fail due to the adverse physiological reactions they cause within the human body, such as infection and inflammation. The surface modification of biomaterials is an economical and effective method by which biocompatibility and biofunctionality can be achieved while preserving the favorable bulk characteristics of the biomaterial, such as strength and inertness. Amongst the numerous surface modification techniques available, plasma surface modification affords device manufacturers a flexible and environmentally friendly process that enables tailoring of the surface morphology, structure, composition, and properties of the material to a specific need. There are a vast range of possible applications of plasma modification in biomaterial applications, however, the focus of this review paper is on processes that can be used to develop surface morphologies and chemical structures for the prevention of adhesion and proliferation of pathogenic bacteria on the surfaces of in-dwelling medical devices. As such, the fundamental principles of bacterial cell attachment and biofilm formation are also discussed. Functional organic plasma polymerised coatings are also discussed for their potential as biosensitive interfaces, connecting inorganic/metallic electronic devices with their physiological environments.
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Affiliation(s)
- Kateryna Bazaka
- Electronic Materials Research Laboratory, School of Engineering and Physical Sciences, James Cook University, Townsville, Queensland, Australia
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187
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Sandoval CM, Baker SL, Jansen K, Metzner SI, Sousa MC. Crystal structure of BamD: an essential component of the β-Barrel assembly machinery of gram-negative bacteria. J Mol Biol 2011; 409:348-57. [PMID: 21463635 DOI: 10.1016/j.jmb.2011.03.035] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 03/15/2011] [Accepted: 03/16/2011] [Indexed: 01/28/2023]
Abstract
Folding and insertion of integral β-barrel proteins in the outer membrane (OM) is an essential process for Gram-negative bacteria that requires the β-barrel assembly machinery (BAM). Efficient OM protein (OMP) folding and insertion appears to require a consensus C-terminal signal in OMPs characterized by terminal F or W residues. The BAM complex is embedded in the OM and, in Escherichia coli, consists of the β-barrel BamA and four lipoproteins BamBCDE. BamA and BamD are broadly distributed across all species of Gram-negative bacteria, whereas the other components are present in only a subset of species. BamA and BamD are also essential for viability, suggesting that these two proteins constitute the functional core of the bacterial BAM complex. Here, we present the crystal structure of BamD from the thermophilic bacteria Rhodothermus marinus refined to 2.15 Å resolution. The protein contains five tetratricopeptide repeats (TPRs) organized into two offset tandems, each capped by a terminal helix. The N-terminal domain contains three TPRs and displays remarkable structural similarity with proteins that recognize targeting signals in extended conformations. The C-terminal domain harbors the remaining two TPRs and previously described mutations that impair binding to other BAM components map to this domain. Therefore, the structure suggests a model where the C-terminal domain provides a scaffold for interaction with BAM components, while the N-terminal domain participates in interaction with the substrates, either recognizing the C-terminal consensus sequence or binding unfolded OMP intermediates.
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Affiliation(s)
- Cristina M Sandoval
- Department of Chemistry and Biochemistry, University of Colorado at Boulder, USA
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188
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Collin S, Guilvout I, Nickerson NN, Pugsley AP. Sorting of an integral outer membrane protein via the lipoprotein-specific Lol pathway and a dedicated lipoprotein pilotin. Mol Microbiol 2011; 80:655-65. [PMID: 21338419 DOI: 10.1111/j.1365-2958.2011.07596.x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The lipoprotein PulS is a dedicated chaperone that is required to target the secretin PulD to the outer membrane in Klebsiella or Escherichia coli, and to protect it from proteolysis. Here, we present indirect evidence that PulD protomers do not assemble into the secretin dodecamer before they reach the outer membrane, and that PulS reaches the outer membrane in a soluble heterodimer with the general lipoprotein chaperone LolA. However, we could not find any direct evidence for PulD protomer association with the PulS-LolA heterodimer. Instead, in cells producing PulD and a permanently locked PulS-LolA dimer (in which LolA carries an R43L substitution that prevents lipoprotein transfer to LolB in the outer membrane), LolAR43L was found in the inner membrane, probably still associated with PulS bound to PulD that had been incorrectly targeted because of the LolAR43L substitution. It is speculated that PulD protomers normally cross the periplasm together with PulS bound to LolA but when the latter cannot be separated (due to the mutation in lolA), the PulD protomers form dodecamers that insert into the inner membrane.
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Affiliation(s)
- Séverine Collin
- Institut Pasteur, Molecular Genetics Unit, Microbiology Department, 75015 Paris, France
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189
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Abstract
It has been known for many years that the small lipoprotein Lpp, which is the most abundant protein in E. coli, exists in two forms. The 'bound' form of the protein is tethered to the outer membrane (OM) by its N-terminal lipid moiety and covalently attached to the cell wall by its C-terminal lysine residue. The exact location of the 'free' form, however, has never been determined. In this issue of Molecular Microbiology, Cowles et al. demonstrate that the free form of Lpp is an integral OM protein whose C-terminus is exposed on the cell surface. The new study provides the first example of a lipoprotein that has a dual localization and adds to a growing body of evidence that lipoproteins can span the OM despite the lack of an obvious transmembrane segment. Furthermore, the new results raise intriguing questions about the assembly of both lipoproteins and other types of OM proteins.
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Affiliation(s)
- Harris D Bernstein
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
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190
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Bennion D, Charlson ES, Coon E, Misra R. Dissection of β-barrel outer membrane protein assembly pathways through characterizing BamA POTRA 1 mutants of Escherichia coli. Mol Microbiol 2011; 77:1153-71. [PMID: 20598079 DOI: 10.1111/j.1365-2958.2010.07280.x] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BamA of Escherichia coli is an essential component of the hetero-oligomeric machinery that mediates β-barrel outer membrane protein (OMP) assembly. The C- and N-termini of BamA fold into trans-membrane β-barrel and five soluble POTRA domains respectively. Detailed characterization of BamA POTRA 1 missense and deletion mutants revealed two competing OMP assembly pathways, one of which is followed by the archetypal trimeric β-barrel OMPs, OmpF and LamB, and is dependent on POTRA 1. Interestingly, our data suggest that BamA also requires its POTRA 1 domain for proper assembly. The second pathway is independent of POTRA 1 and is exemplified by TolC. Site-specific cross-linking analysis revealed that the POTRA 1 domain of BamA interacts with SurA, a periplasmic chaperone required for the assembly of OmpF and LamB, but not that of TolC and BamA. The data suggest that SurA and BamA POTRA 1 domain function in concert to assist folding and assembly of most β-barrel OMPs except for TolC, which folds into a unique soluble α-helical barrel and an OM-anchored β-barrel. The two assembly pathways finally merge at some step beyond POTRA 1 but presumably before membrane insertion, which is thought to be catalysed by the trans-membrane β-barrel domain of BamA.
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Affiliation(s)
- Drew Bennion
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
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191
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Bechet E, Gruszczyk J, Terreux R, Gueguen-Chaignon V, Vigouroux A, Obadia B, Cozzone AJ, Nessler S, Grangeasse C. Identification of structural and molecular determinants of the tyrosine-kinase Wzc and implications in capsular polysaccharide export. Mol Microbiol 2011; 77:1315-25. [PMID: 20633230 DOI: 10.1111/j.1365-2958.2010.07291.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Capsular polysaccharides are well-established virulence factors of pathogenic bacteria. Their biosynthesis and export are regulated within the transmembrane polysaccharide assembly machinery by the autophosphorylation of atypical tyrosine-kinases, named BY-kinases. However, the accurate functioning of these tyrosine-kinases remains unknown. Here, we report the crystal structure of the non-phosphorylated cytoplasmic domain of the tyrosine-kinase Wzc from Escherichia coli in complex with ADP showing that it forms a ring-shaped octamer. Mutational analysis demonstrates that a conserved EX(2) RX(2) R motif involved in subunit interactions is essential for polysaccharide export. We also elucidate the role of a putative internal regulatory tyrosine and we show that BY-kinases from proteobacteria autophosphorylate on their C-terminal tyrosine cluster via a single-step intermolecular mechanism. This structure-function analysis also allows us to demonstrate that two different parts of a conserved basic region called the RK-cluster are essential for polysaccharide export and for kinase activity respectively. Based on these data, we revisit the dichotomy made between BY-kinases from proteobacteria and firmicutes and we propose a unique process of oligomerization and phosphorylation. We also reassess the function of BY-kinases in the capsular polysaccharide assembly machinery.
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Affiliation(s)
- Emmanuelle Bechet
- Institut de Biologie et Chimie des Protéines, CNRS, Université Lyon 1, Université de Lyon, 69367 Lyon, France
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192
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Guilvout I, Nickerson NN, Chami M, Pugsley AP. Multimerization-defective variants of dodecameric secretin PulD. Res Microbiol 2011; 162:180-90. [DOI: 10.1016/j.resmic.2011.01.006] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Revised: 01/14/2011] [Indexed: 10/18/2022]
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193
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Bacterial Extracellular Polysaccharides. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2011; 715:213-26. [DOI: 10.1007/978-94-007-0940-9_13] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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194
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Outer membrane translocons: structural insights into channel formation. Trends Microbiol 2010; 19:40-8. [PMID: 21130656 DOI: 10.1016/j.tim.2010.10.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 10/18/2010] [Accepted: 10/29/2010] [Indexed: 01/26/2023]
Abstract
Gram-negative bacteria need to maintain the integrity of their outer membrane while also regulating the secretion of toxins and other macromolecules. A variety of dedicated outer membrane proteins (OMPs) facilitate this process. Recent structural work has shown that some of these proteins adopt classical β-barrel transmembrane structures and rely on structural changes within the barrel lumen to allow passage of substrate proteins. Other secretion systems have OMP components which use transmembrane α-helices and appear to function in a different way. Here we review a selection of recent structural studies which have major ramifications for our understanding of the passage of macromolecules across the outer membrane.
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195
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Bushell SR, Lou H, Wallat GD, Beis K, Whitfield C, Naismith JH. Crystallization and preliminary diffraction analysis of Wzi, a member of the capsule export and assembly pathway in Escherichia coli. Acta Crystallogr Sect F Struct Biol Cryst Commun 2010; 66:1621-5. [PMID: 21139210 PMCID: PMC2998369 DOI: 10.1107/s1744309110040546] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2010] [Accepted: 10/09/2010] [Indexed: 11/12/2022]
Abstract
External polysaccharide capsules provide a physical barrier that is employed by many species of bacteria for the purposes of host evasion and persistence. Wzi is a 53 kDa outer membrane β-barrel protein that is thought to play a role in the attachment of group 1 capsular polysaccharides to the cell surface. The purification and crystallization of an Escherichia coli homologue of Wzi is reported and diffraction data from native and selenomethionine-incorporated protein crystals are presented. Crystals of C-terminally His6-tagged Wzi diffracted to 2.8 Å resolution. Data processing showed that the crystals belonged to the orthorhombic space group C222, with unit-cell parameters a=128.8, b=152.8, c=94.4 Å, α=β=γ=90°. A His-tagged selenomethionine-containing variant of Wzi has also been crystallized in the same space group and diffraction data have been recorded to 3.8 Å resolution. Data processing shows that the variant crystal has similar unit-cell parameters to the native crystal.
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Affiliation(s)
- Simon R. Bushell
- Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews KY16 9ST, Scotland
| | - Hubing Lou
- Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews KY16 9ST, Scotland
| | - Gregor D. Wallat
- Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews KY16 9ST, Scotland
| | - Konstantinos Beis
- Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews KY16 9ST, Scotland
| | - Chris Whitfield
- Department of Molecular and Cell Biology, University of Guelph, Ontario N1G 2W1, Canada
| | - James H. Naismith
- Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews KY16 9ST, Scotland
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196
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Reckseidler-Zenteno SL, Viteri DF, Moore R, Wong E, Tuanyok A, Woods DE. Characterization of the type III capsular polysaccharide produced by Burkholderia pseudomallei. J Med Microbiol 2010; 59:1403-1414. [DOI: 10.1099/jmm.0.022202-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Burkholderia pseudomallei has been shown to produce more than one capsular polysaccharide (CPS). Analysis of the B. pseudomallei genome has revealed that the organism contains four CPS operons (I–IV). One of these operons (CPS III) was selected for further study. Comparative sequencing analysis revealed that the genes encoding CPS III are present in B. pseudomallei and Burkholderia thailandensis but not in Burkholderia mallei. In this study, CPS III was not found to contribute to the virulence of B. pseudomallei. Strains containing mutations in CPS III had the same LD50 value as the wild-type when tested in an animal infection model. Production of CPS III was shown to be induced in water but inhibited in 30 % normal human serum using a lux reporter fusion assay. Microarray analysis of capsule gene expression in infected hamsters revealed that the genes encoding CPS III were not significantly expressed in vivo compared with the genes encoding the previously characterized mannoheptose capsule (CPS I), which is an important virulence factor in B. pseudomallei. Glycosyl-composition analysis by combined GC/MS indicated that the CPS III genes are involved in the synthesis of a capsule composed of galactose, glucose, mannose and xylose.
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Affiliation(s)
- Shauna L. Reckseidler-Zenteno
- Centre for Science, Athabasca University, Athabasca, AB T9S 9Z9, Canada
- Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, AB T2N 4N1, Canada
| | - Duber-Frey Viteri
- Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, AB T2N 4N1, Canada
| | - Richard Moore
- Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, AB T2N 4N1, Canada
| | - Erica Wong
- Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, AB T2N 4N1, Canada
| | - Apichai Tuanyok
- Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, AB T2N 4N1, Canada
| | - Donald E. Woods
- Department of Microbiology and Infectious Diseases, University of Calgary Health Sciences Center, Calgary, AB T2N 4N1, Canada
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197
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Mizianty MJ, Kurgan L. Improved identification of outer membrane beta barrel proteins using primary sequence, predicted secondary structure, and evolutionary information. Proteins 2010; 79:294-303. [DOI: 10.1002/prot.22882] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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198
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Abstract
Since the proposal of the signal hypothesis on protein subcellular sorting, a number of computational analyses have been performed in this field. A typical example is the development of prediction algorithms for the subcellular localization sites of input protein sequences. In this review, we mainly focus on the biological grounds of the prediction methods rather than the algorithmic issues because we believe the former will be more fruitful for future development. Recent advances on the study of protein sorting signals will hopefully be incorporated into future prediction methods. Unfortunately, many of the state-of-the-art methods are published without sufficient objective tests. In fact, a simple test employed in this article shows that the performance of specifically developed predictors is not significantly better than that of a homology search. We suspect that this is a general problem associated with the interpretation of genome sequences, which have evolved through gene duplication and speciation.
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Affiliation(s)
- Kenichiro Imai
- Computational Biology Research Center, AIST, Tokyo, Japan
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199
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Three-dimensional structure of TspO by electron cryomicroscopy of helical crystals. Structure 2010; 18:677-87. [PMID: 20541505 PMCID: PMC2911597 DOI: 10.1016/j.str.2010.03.001] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 02/08/2010] [Accepted: 03/02/2010] [Indexed: 11/24/2022]
Abstract
The 18 kDa TSPO protein is a polytopic mitochondrial outer membrane protein involved in a wide range of physiological functions and pathologies, including neurodegeneration and cancer. The pharmacology of TSPO has been extensively studied, but little is known about its biochemistry, oligomeric state, and structure. We have expressed, purified, and characterized a homologous protein, TspO from Rhodobacter sphaeroides, and reconstituted it as helical crystals. Using electron cryomicroscopy and single-particle helical reconstruction, we have determined a three-dimensional structure of TspO at 10 Å resolution. The structure suggests that monomeric TspO comprises five transmembrane α helices that form a homodimer, which is consistent with the dimeric state observed in detergent solution. Furthermore, the arrangement of transmembrane domains of individual TspO subunits indicates a possibility of two substrate translocation pathways per dimer. The structure provides the first insight into the molecular architecture of TSPO/PBR protein family that will serve as a framework for future studies.
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200
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The K1 capsular polysaccharide of Acinetobacter baumannii strain 307-0294 is a major virulence factor. Infect Immun 2010; 78:3993-4000. [PMID: 20643860 DOI: 10.1128/iai.00366-10] [Citation(s) in RCA: 229] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Acinetobacter baumannii is a pathogen of increasing medical importance with a propensity to be multidrug resistant, thereby making treatment challenging. Little is known of virulence traits in A. baumannii. To identify virulence factors and potential drug targets, random transposon (Tn) mutants derived from the A. baumannii strain AB307-0294 were screened to identify genes essential for growth in human ascites fluid in vitro, an inflammatory exudative fluid. These studies led to the identification of two genes that were predicted to be required for capsule polymerization and assembly. The first, ptk, encodes a putative protein tyrosine kinase (PTK), and the second, epsA, encodes a putative polysaccharide export outer membrane protein (EpsA). Monoclonal antibodies used in flow cytometric and Western analyses confirmed that these genes are required for a capsule-positive phenotype. A capsule-positive phenotype significantly optimized growth in human ascites fluid, survival in human serum, and survival in a rat soft tissue infection model. Importantly, the clearance of the capsule-minus mutants AB307.30 (ptk mutant, capsule minus) and AB307.45 (epsA mutant, capsule minus) was complete and durable. These data demonstrated that the K1 capsule from AB307-0294 was an important protectin. Further, these data suggested that conserved proteins, which contribute to the capsule-positive phenotype, are potential antivirulence drug targets. Therefore, the results from this study have important biologic and translational implications and, to the best of our knowledge, are the first to address the role of capsule in the pathogenesis of A. baumannii infection.
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