51
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Fantappiè L, Irene C, De Santis M, Armini A, Gagliardi A, Tomasi M, Parri M, Cafardi V, Bonomi S, Ganfini L, Zerbini F, Zanella I, Carnemolla C, Bini L, Grandi A, Grandi G. Some Gram-negative Lipoproteins Keep Their Surface Topology When Transplanted from One Species to Another and Deliver Foreign Polypeptides to the Bacterial Surface. Mol Cell Proteomics 2017; 16:1348-1364. [PMID: 28483926 PMCID: PMC5500766 DOI: 10.1074/mcp.m116.065094] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2016] [Revised: 05/05/2017] [Indexed: 11/29/2022] Open
Abstract
In Gram-negative bacteria, outer membrane-associated lipoproteins can either face the periplasm or protrude out of the bacterial surface. The mechanisms involved in lipoprotein transport through the outer membrane are not fully elucidated. Some lipoproteins reach the surface by using species-specific transport machinery. By contrast, a still poorly characterized group of lipoproteins appears to always cross the outer membrane, even when transplanted from one organism to another. To investigate such lipoproteins, we tested the expression and compartmentalization in E. coli of three surface-exposed lipoproteins, two from Neisseria meningitidis (Nm-fHbp and NHBA) and one from Aggregatibacter actinomycetemcomitans (Aa-fHbp). We found that all three lipoproteins were lipidated and compartmentalized in the E. coli outer membrane and in outer membrane vesicles. Furthermore, fluorescent antibody cell sorting analysis, proteolytic surface shaving, and confocal microscopy revealed that all three proteins were also exposed on the surface of the outer membrane. Removal or substitution of the first four amino acids following the lipidated cysteine residue and extensive deletions of the C-terminal regions in Nm-fHbp did not prevent the protein from reaching the surface of the outer membrane. Heterologous polypeptides, fused to the C termini of Nm-fHbp and NHBA, were efficiently transported to the E. coli cell surface and compartmentalized in outer membrane vesicles, demonstrating that these lipoproteins can be exploited in biotechnological applications requiring Gram-negative bacterial surface display of foreign polypeptides.
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Affiliation(s)
- Laura Fantappiè
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Carmela Irene
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Micaela De Santis
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Alessandro Armini
- §Functional Proteomics Lab., Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy
| | - Assunta Gagliardi
- §Functional Proteomics Lab., Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy
| | - Michele Tomasi
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Matteo Parri
- ¶Toscana Life Sciences Scientific Park, Via Fiorentina, 1 53100, Siena, Italy
| | - Valeria Cafardi
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Serena Bonomi
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Luisa Ganfini
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Francesca Zerbini
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Ilaria Zanella
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy
| | - Chiara Carnemolla
- §Functional Proteomics Lab., Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy
| | - Luca Bini
- §Functional Proteomics Lab., Department of Life Sciences, University of Siena, Via Aldo Moro 2, 53100 Siena, Italy
| | - Alberto Grandi
- ¶Toscana Life Sciences Scientific Park, Via Fiorentina, 1 53100, Siena, Italy
| | - Guido Grandi
- From the ‡Synthetic and Structural Vaccinology Unit, CIBIO, University of Trento, Via Sommarive, 9, 38123 Povo, Trento, Italy;
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52
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Redefining the essential trafficking pathway for outer membrane lipoproteins. Proc Natl Acad Sci U S A 2017; 114:4769-4774. [PMID: 28416660 DOI: 10.1073/pnas.1702248114] [Citation(s) in RCA: 85] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The outer membrane (OM) of Gram-negative bacteria is a permeability barrier and an intrinsic antibiotic resistance factor. Lipoproteins are OM components that function in cell wall synthesis, diverse secretion systems, and antibiotic efflux pumps. Moreover, each of the essential OM machines that assemble the barrier requires one or more lipoproteins. This dependence is thought to explain the essentiality of the periplasmic chaperone LolA and its OM receptor LolB that traffic lipoproteins to the OM. However, we show that in strains lacking substrates that are toxic when mislocalized, both LolA and LolB can be completely bypassed by activating an envelope stress response without compromising trafficking of essential lipoproteins. We identify the Cpx stress response as a monitor of lipoprotein trafficking tasked with protecting the cell from mislocalized lipoproteins. Moreover, our findings reveal that an alternate trafficking pathway exists that can, under certain conditions, bypass the functions of LolA and LolB, implying that these proteins do not perform any truly essential mechanistic steps in lipoprotein trafficking. Instead, these proteins' key function is to prevent lethal accumulation of mislocalized lipoproteins.
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53
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Comprehensive Spatial Analysis of the Borrelia burgdorferi Lipoproteome Reveals a Compartmentalization Bias toward the Bacterial Surface. J Bacteriol 2017; 199:JB.00658-16. [PMID: 28069820 DOI: 10.1128/jb.00658-16] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 01/03/2017] [Indexed: 12/13/2022] Open
Abstract
The Lyme disease spirochete Borrelia burgdorferi is unique among bacteria in its large number of lipoproteins that are encoded by a small, exceptionally fragmented, and predominantly linear genome. Peripherally anchored in either the inner or outer membrane and facing either the periplasm or the external environment, these lipoproteins assume varied roles. A prominent subset of lipoproteins functioning as the apparent linchpins of the enzootic tick-vertebrate infection cycle have been explored as vaccine targets. Yet, most of the B. burgdorferi lipoproteome has remained uncharacterized. Here, we comprehensively and conclusively localize the B. burgdorferi lipoproteome by applying established protein localization assays to a newly generated epitope-tagged lipoprotein expression library and by validating the obtained individual protein localization results using a sensitive global mass spectrometry approach. The derived consensus localization data indicate that 86 of the 125 analyzed lipoproteins encoded by B. burgdorferi are secreted to the bacterial surface. Thirty-one of the remaining 39 periplasmic lipoproteins are retained in the inner membrane, with only 8 lipoproteins being anchored in the periplasmic leaflet of the outer membrane. The localization of 10 lipoproteins was further defined or revised, and 52 surface and 23 periplasmic lipoproteins were newly localized. Cross-referencing prior studies revealed that the borrelial surface lipoproteome contributing to the host-pathogen interface is encoded predominantly by plasmids. Conversely, periplasmic lipoproteins are encoded mainly by chromosomal loci. These studies close a gap in our understanding of the functional lipoproteome of an important human pathogen and set the stage for more in-depth studies of thus-far-neglected spirochetal lipoproteins.IMPORTANCE The small and exceptionally fragmented genome of the Lyme disease spirochete Borrelia burgdorferi encodes over 120 lipoproteins. Studies in the field have predominantly focused on a relatively small number of surface lipoproteins that play important roles in the transmission and pathogenesis of this global human pathogen. Yet, a comprehensive spatial assessment of the entire borrelial lipoproteome has been missing. The current study newly identifies 52 surface and 23 periplasmic lipoproteins. Overall, two-thirds of the B. burgdorferi lipoproteins localize to the surface, while outer membrane lipoproteins facing the periplasm are rare. This analysis underscores the dominant contribution of lipoproteins to the spirochete's rather complex and adaptable host-pathogen interface, and it encourages further functional exploration of its lipoproteome.
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54
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Narita SI, Tokuda H. Bacterial lipoproteins; biogenesis, sorting and quality control. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1862:1414-1423. [PMID: 27871940 DOI: 10.1016/j.bbalip.2016.11.009] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 11/11/2016] [Accepted: 11/14/2016] [Indexed: 12/20/2022]
Abstract
Bacterial lipoproteins are a subset of membrane proteins localized on either leaflet of the lipid bilayer. These proteins are anchored to membranes through their N-terminal lipid moiety attached to a conserved Cys. Since the protein moiety of most lipoproteins is hydrophilic, they are expected to play various roles in a hydrophilic environment outside the cytoplasmic membrane. Gram-negative bacteria such as Escherichia coli possess an outer membrane, to which most lipoproteins are sorted. The Lol pathway plays a central role in the sorting of lipoproteins to the outer membrane after lipoprotein precursors are processed to mature forms in the cytoplasmic membrane. Most lipoproteins are anchored to the inner leaflet of the outer membrane with their protein moiety in the periplasm. However, recent studies indicated that some lipoproteins further undergo topology change in the outer membrane, and play critical roles in the biogenesis and quality control of the outer membrane. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.
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Affiliation(s)
| | - Hajime Tokuda
- University of Morioka, Takizawa, Iwate 020-0694, Japan.
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55
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Grabowicz M, Silhavy TJ. Envelope Stress Responses: An Interconnected Safety Net. Trends Biochem Sci 2016; 42:232-242. [PMID: 27839654 DOI: 10.1016/j.tibs.2016.10.002] [Citation(s) in RCA: 95] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 10/12/2016] [Accepted: 10/17/2016] [Indexed: 12/14/2022]
Abstract
The Escherichia coli cell envelope is a protective barrier at the frontline of interaction with the environment. Fidelity of envelope biogenesis must be monitored to establish and maintain a contiguous barrier. Indeed, the envelope must also be repaired and modified in response to environmental assaults. Envelope stress responses (ESRs) sense envelope damage or defects and alter the transcriptome to mitigate stress. Here, we review recent insights into the stress-sensing mechanisms of the σE and Cpx systems and the interaction of these ESRs. Small RNAs (sRNAs) are increasingly prominent regulators of the transcriptional response to stress. These fast-acting regulators also provide avenues for inter-ESR regulation that could be important when cells face multiple contemporaneous stresses, as is the case during infection.
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Affiliation(s)
- Marcin Grabowicz
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Thomas J Silhavy
- Department of Molecular Biology, Princeton University, Princeton, NJ, USA.
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56
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A penicillin-binding protein inhibits selection of colistin-resistant, lipooligosaccharide-deficient Acinetobacter baumannii. Proc Natl Acad Sci U S A 2016; 113:E6228-E6237. [PMID: 27681618 DOI: 10.1073/pnas.1611594113] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The Gram-negative bacterial outer membrane fortifies the cell against environmental toxins including antibiotics. Unique glycolipids called lipopolysaccharide/lipooligosaccharide (LPS/LOS) are enriched in the cell-surface monolayer of the outer membrane and promote antimicrobial resistance. Colistin, which targets the lipid A domain of LPS/LOS to lyse the cell, is the last-line treatment for multidrug-resistant Gram-negative infections. Lipid A is essential for the survival of most Gram-negative bacteria, but colistin-resistant Acinetobacter baumannii lacking lipid A were isolated after colistin exposure. Previously, strain ATCC 19606 was the only A. baumannii strain demonstrated to subsist without lipid A. Here, we show that other A. baumannii strains can also survive without lipid A, but some cannot, affording a unique model to study endotoxin essentiality. We assessed the capacity of 15 clinical A. baumannii isolates including 9 recent clinical isolates to develop colistin resistance through inactivation of the lipid A biosynthetic pathway, the products of which assemble the LOS precursor. Our investigation determined that expression of the well-conserved penicillin-binding protein (PBP) 1A, prevented LOS-deficient colony isolation. The glycosyltransferase activity of PBP1A, which aids in the polymerization of the peptidoglycan cell wall, was lethal to LOS-deficient A. baumannii Global transcriptomic analysis of a PBP1A-deficient mutant and four LOS-deficient A. baumannii strains showed a concomitant increase in transcription of lipoproteins and their transporters. Examination of the LOS-deficient A. baumannii cell surface demonstrated that specific lipoproteins were overexpressed and decorated the cell surface, potentially compensating for LOS removal. This work expands our knowledge of lipid A essentiality and elucidates a drug resistance mechanism.
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57
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Szewczyk J, Collet JF. The Journey of Lipoproteins Through the Cell: One Birthplace, Multiple Destinations. Adv Microb Physiol 2016; 69:1-50. [PMID: 27720009 DOI: 10.1016/bs.ampbs.2016.07.003] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Bacterial lipoproteins are a very diverse group of proteins characterized by the presence of an N-terminal lipid moiety that serves as a membrane anchor. Lipoproteins have a wide variety of crucial functions, ranging from envelope biogenesis to stress response. In Gram-negative bacteria, lipoproteins can be targeted to various destinations in the cell, including the periplasmic side of the cytoplasmic or outer membrane, the cell surface or the external milieu. The sorting mechanisms have been studied in detail in Escherichia coli, but exceptions to the rules established in this model bacterium exist in other bacteria. In this chapter, we will present the current knowledge on lipoprotein sorting in the cell. Our particular focus will be on the surface-exposed lipoproteins that appear to be much more common than previously assumed. We will discuss the different targeting strategies, provide numerous examples of surface-exposed lipoproteins and discuss the techniques used to assess their surface exposure.
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Affiliation(s)
- J Szewczyk
- WELBIO, Brussels, Belgium; de Duve Institute, Université catholique de Louvain, Brussels, Belgium
| | - J-F Collet
- WELBIO, Brussels, Belgium; de Duve Institute, Université catholique de Louvain, Brussels, Belgium.
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58
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Abstract
In order to relate the structural architecture of the BAM complex to its function in outer membrane protein assembly, the arrangement of each component within the complex is vital. This chapter explores the structure and topology of BamC, using a range of biochemical techniques to probe the topology and surface exposure.
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Affiliation(s)
- Chaille T Webb
- Department of Microbiology, Monash University, Building 77, 23 Innovation Walk, Clayton Campus, Melbourne, VIC, 3800, Australia.
| | - Trevor Lithgow
- Department of Microbiology, Monash University, Building 77, 23 Innovation Walk, Clayton Campus, Melbourne, VIC, 3800, Australia.
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59
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Konovalova A, Silhavy TJ. Outer membrane lipoprotein biogenesis: Lol is not the end. Philos Trans R Soc Lond B Biol Sci 2016; 370:rstb.2015.0030. [PMID: 26370942 DOI: 10.1098/rstb.2015.0030] [Citation(s) in RCA: 90] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Bacterial lipoproteins are lipid-anchored proteins that contain acyl groups covalently attached to the N-terminal cysteine residue of the mature protein. Lipoproteins are synthesized in precursor form with an N-terminal signal sequence (SS) that targets translocation across the cytoplasmic or inner membrane (IM). Lipid modification and SS processing take place at the periplasmic face of the IM. Outer membrane (OM) lipoproteins take the localization of lipoproteins (Lol) export pathway, which ends with the insertion of the N-terminal lipid moiety into the inner leaflet of the OM. For many lipoproteins, the biogenesis pathway ends here. We provide examples of lipoproteins that adopt complex topologies in the OM that include transmembrane and surface-exposed domains. Biogenesis of such lipoproteins requires additional steps beyond the Lol pathway. In at least one case, lipoprotein sequences reach the cell surface by being threaded through the lumen of a beta-barrel protein in an assembly reaction that requires the heteropentomeric Bam complex. The inability to predict surface exposure reinforces the importance of experimental verification of lipoprotein topology and we will discuss some of the methods used to study OM protein topology.
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Affiliation(s)
- Anna Konovalova
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Washington Road, Princeton, NJ 08544, USA
| | - Thomas J Silhavy
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Washington Road, Princeton, NJ 08544, USA
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60
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Henderson JC, Zimmerman SM, Crofts AA, Boll JM, Kuhns LG, Herrera CM, Trent MS. The Power of Asymmetry: Architecture and Assembly of the Gram-Negative Outer Membrane Lipid Bilayer. Annu Rev Microbiol 2016; 70:255-78. [PMID: 27359214 DOI: 10.1146/annurev-micro-102215-095308] [Citation(s) in RCA: 141] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Determining the chemical composition of biological materials is paramount to the study of natural phenomena. Here, we describe the composition of model gram-negative outer membranes, focusing on the predominant assembly, an asymmetrical bilayer of lipid molecules. We also give an overview of lipid biosynthetic pathways and molecular mechanisms that organize this material into the outer membrane bilayer. An emphasis is placed on the potential of these pathways as targets for antibiotic development. We discuss deviations in composition, through bacterial cell surface remodeling, and alternative modalities to the asymmetric lipid bilayer. Outer membrane lipid alterations of current microbiological interest, such as lipid structures found in commensal bacteria, are emphasized. Additionally, outer membrane components could potentially be engineered to develop vaccine platforms. Observations related to composition and assembly of gram-negative outer membranes will continue to generate novel discoveries, broaden biotechnologies, and reveal profound mysteries to compel future research.
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Affiliation(s)
- Jeremy C Henderson
- Department of Molecular Biosciences, The University of Texas at Austin, Texas 78712
| | - Shawn M Zimmerman
- Department of Infectious Diseases, The University of Georgia, Athens, Georgia 30602;
| | - Alexander A Crofts
- Department of Molecular Biosciences, The University of Texas at Austin, Texas 78712
| | - Joseph M Boll
- Department of Molecular Biosciences, The University of Texas at Austin, Texas 78712
| | - Lisa G Kuhns
- Department of Infectious Diseases, The University of Georgia, Athens, Georgia 30602;
| | - Carmen M Herrera
- Department of Infectious Diseases, The University of Georgia, Athens, Georgia 30602;
| | - M Stephen Trent
- Department of Infectious Diseases, The University of Georgia, Athens, Georgia 30602;
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61
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Chan K, Nasereddin T, Alter L, Centurion-Lara A, Giacani L, Parveen N. Treponema pallidum Lipoprotein TP0435 Expressed in Borrelia burgdorferi Produces Multiple Surface/Periplasmic Isoforms and mediates Adherence. Sci Rep 2016; 6:25593. [PMID: 27161310 PMCID: PMC4861935 DOI: 10.1038/srep25593] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 04/18/2016] [Indexed: 12/17/2022] Open
Abstract
The ability of Treponema pallidum, the syphilis spirochete to colonize various tissues requires the presence of surface-exposed adhesins that have been difficult to identify due to the inability to culture and genetically manipulate T. pallidum. Using a Borrelia burgdorferi-based heterologous system and gain-in-function approach, we show for the first time that a highly immunogenic lipoprotein TP0435 can be differentially processed into multiple isoforms with one variant stochastically displayed on the spirochete surface. TP0435 was previously believed to be exclusively located in T. pallidum periplasm. Furthermore, non-adherent B. burgdorferi strain expressing TP0435 acquires the ability to bind to a variety of host cells including placental cells and exhibits slow opsonophagocytosis in vitro similar to poor ex vivo phagocytosis of T. pallidum by host macrophages reported previously. This phenomenon of production of both surface and periplasmic immunogenic lipoprotein isoforms has possible implications in immune evasion of the obligate pathogen T. pallidum during infection.
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Affiliation(s)
- Kamfai Chan
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers-New Jersey Medical School, Newark, NJ 07103, USA
| | - Thayer Nasereddin
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers-New Jersey Medical School, Newark, NJ 07103, USA
| | - Laura Alter
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers-New Jersey Medical School, Newark, NJ 07103, USA
| | | | - Lorenzo Giacani
- Department of Medicine, University of Washington, Seattle, WA 98104, USA
| | - Nikhat Parveen
- Department of Microbiology, Biochemistry and Molecular Genetics, Rutgers-New Jersey Medical School, Newark, NJ 07103, USA
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62
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Surmann K, Ćudić E, Hammer E, Hunke S. Molecular and proteome analyses highlight the importance of the Cpx envelope stress system for acid stress and cell wall stability in Escherichia coli. Microbiologyopen 2016; 5:582-96. [PMID: 27039284 PMCID: PMC4985592 DOI: 10.1002/mbo3.353] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 02/10/2016] [Accepted: 02/15/2016] [Indexed: 01/24/2023] Open
Abstract
Two‐component systems (TCS) play a pivotal role for bacteria in stress regulation and adaptation. However, it is not well understood how these systems are modulated to meet bacterial demands. Especially, for those TCS using an accessory protein to integrate additional signals, no data concerning the role of the accessory proteins within the coordination of the response is available. The Cpx envelope stress two‐component system, composed of the sensor kinase CpxA and the response regulator CpxR, is orchestrated by the periplasmic protein CpxP which detects misfolded envelope proteins and inhibits the Cpx system in unstressed cells. Using selected reaction monitoring, we observed that the amount of CpxA and CpxR, as well as their stoichiometry, are only marginally affected, but that a 10‐fold excess of CpxP over CpxA is needed to switch off the Cpx system. Moreover, the relative quantification of the proteome identified not only acid stress response as a new indirect target of the Cpx system, but also suggests a general function of the Cpx system for cell wall stability.
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Affiliation(s)
- Kristin Surmann
- Department of Functional Genomics, Interfaculty Institute of Genetics and Functional Genomics, University Medicine Greifswald, Friedrich-Ludwig-Jahn-Straße 15A, Greifswald, 17475, Germany
| | - Emina Ćudić
- FB 5 Microbiology, Department of Biology/Chemistry, University Osnabrück, Barbarastraße 11, Osnabrück, 49076,, Germany
| | - Elke Hammer
- Department of Functional Genomics, Interfaculty Institute of Genetics and Functional Genomics, University Medicine Greifswald, Friedrich-Ludwig-Jahn-Straße 15A, Greifswald, 17475, Germany
| | - Sabine Hunke
- FB 5 Microbiology, Department of Biology/Chemistry, University Osnabrück, Barbarastraße 11, Osnabrück, 49076,, Germany
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63
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Disruption of lipid homeostasis in the Gram-negative cell envelope activates a novel cell death pathway. Proc Natl Acad Sci U S A 2016; 113:E1565-74. [PMID: 26929379 DOI: 10.1073/pnas.1601375113] [Citation(s) in RCA: 119] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Gram-negative bacteria balance synthesis of the outer membrane (OM), cell wall, and cytoplasmic contents during growth via unknown mechanisms. Here, we show that a dominant mutation (designated mlaA*, maintenance of lipid asymmetry) that alters MlaA, a lipoprotein that removes phospholipids from the outer leaflet of the OM of Escherichia coli, increases OM permeability, lipopolysaccharide levels, drug sensitivity, and cell death in stationary phase. Surprisingly, single-cell imaging revealed that death occurs after protracted loss of OM material through vesiculation and blebbing at cell-division sites and compensatory shrinkage of the inner membrane, eventually resulting in rupture and slow leakage of cytoplasmic contents. The death of mlaA* cells was linked to fatty acid depletion and was not affected by membrane depolarization, suggesting that lipids flow from the inner membrane to the OM in an energy-independent manner. Suppressor analysis suggested that the dominant mlaA* mutation activates phospholipase A, resulting in increased levels of lipopolysaccharide and OM vesiculation that ultimately undermine the integrity of the cell envelope by depleting the inner membrane of phospholipids. This novel cell-death pathway suggests that balanced synthesis across both membranes is key to the mechanical integrity of the Gram-negative cell envelope.
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64
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Wilson MM, Bernstein HD. Surface-Exposed Lipoproteins: An Emerging Secretion Phenomenon in Gram-Negative Bacteria. Trends Microbiol 2015; 24:198-208. [PMID: 26711681 DOI: 10.1016/j.tim.2015.11.006] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Revised: 11/17/2015] [Accepted: 11/23/2015] [Indexed: 01/07/2023]
Abstract
Bacterial lipoproteins are hydrophilic proteins that are anchored to a cell membrane by N-terminally linked fatty acids. It is widely believed that nearly all lipoproteins produced by Gram-negative bacteria are either retained in the inner membrane (IM) or transferred to the inner leaflet of the outer membrane (OM). Lipoproteins that are exposed on the cell surface have also been reported but are generally considered to be rare. Results from a variety of recent studies, however, now suggest that the prevalence of surface-exposed lipoproteins has been underestimated. In this review we describe the evidence that the surface exposure of lipoproteins in Gram-negative bacteria is a widespread phenomenon and discuss possible mechanisms by which these proteins might be transported across the OM.
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Affiliation(s)
- Marlena M Wilson
- Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
| | - 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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65
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Goolab S, Roth RL, van Heerden H, Crampton MC. Analyzing the molecular mechanism of lipoprotein localization in Brucella. Front Microbiol 2015; 6:1189. [PMID: 26579096 PMCID: PMC4623201 DOI: 10.3389/fmicb.2015.01189] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 10/12/2015] [Indexed: 01/18/2023] Open
Abstract
Bacterial lipoproteins possess diverse structure and functionality, ranging from bacterial physiology to pathogenic processes. As such many lipoproteins, originating from Brucella are exploited as potential vaccines to countermeasure brucellosis infection in the host. These membrane proteins are translocated from the cytoplasm to the cell membrane where they are anchored peripherally by a multifaceted targeting mechanism. Although much research has focused on the identification and classification of Brucella lipoproteins and their potential use as vaccine candidates for the treatment of Brucellosis, the underlying route for the translocation of these lipoproteins to the outer surface of the Brucella (and other pathogens) outer membrane (OM) remains mostly unknown. This is partly due to the complexity of the organism and evasive tactics used to escape the host immune system, the variation in biological structure and activity of lipoproteins, combined with the complex nature of the translocation machinery. The biosynthetic pathway of Brucella lipoproteins involves a distinct secretion system aiding translocation from the cytoplasm, where they are modified by lipidation, sorted by the lipoprotein localization machinery pathway and thereafter equipped for export to the OM. Surface localized lipoproteins in Brucella may employ a lipoprotein flippase or the β-barrel assembly complex for translocation. This review provides an overview of the characterized Brucella OM proteins that form part of the OM, including a handful of other characterized bacterial lipoproteins and their mechanisms of translocation. Lipoprotein localization pathways in gram negative bacteria will be used as a model to identify gaps in Brucella lipoprotein localization and infer a potential pathway. Of particular interest are the dual topology lipoproteins identified in Escherichia coli and Haemophilus influenza. The localization and topology of these lipoproteins from other gram negative bacteria are well characterized and may be useful to infer a solution to better understand the translocation process in Brucella.
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Affiliation(s)
- Shivani Goolab
- Protein Technologies, Biosciences, Council for Scientific and Industrial ResearchPretoria, South Africa
- Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of PretoriaPretoria, South Africa
| | - Robyn L. Roth
- Protein Technologies, Biosciences, Council for Scientific and Industrial ResearchPretoria, South Africa
| | - Henriette van Heerden
- Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of PretoriaPretoria, South Africa
| | - Michael C. Crampton
- Protein Technologies, Biosciences, Council for Scientific and Industrial ResearchPretoria, South Africa
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Gonzalez T, Gaultney RA, Floden AM, Brissette CA. Escherichia coli lipoprotein binds human plasminogen via an intramolecular domain. Front Microbiol 2015; 6:1095. [PMID: 26500634 PMCID: PMC4595779 DOI: 10.3389/fmicb.2015.01095] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 09/22/2015] [Indexed: 11/13/2022] Open
Abstract
Escherichia coli lipoprotein (Lpp) is a major cellular component that exists in two distinct states, bound-form and free-form. Bound-form Lpp is known to interact with the periplasmic bacterial cell wall, while free-form Lpp is localized to the bacterial cell surface. A function for surface-exposed Lpp has yet to be determined. We hypothesized that the presence of C-terminal lysinses in the surface-exposed region of Lpp would facilitate binding to the host zymogen plasminogen (Plg), a protease commandeered by a number of clinically important bacteria. Recombinant Lpp was synthesized and the binding of Lpp to Plg, the effect of various inhibitors on this binding, and the effects of various mutations of Lpp on Lpp-Plg interactions were examined. Additionally, the ability of Lpp-bound Plg to be converted to active plasmin was analyzed. We determined that Lpp binds Plg via an atypical domain located near the center of mature Lpp that may not be exposed on the surface of intact E. coli according to the current localization model. Finally, we found that Plg bound by Lpp can be converted to active plasmin. While the consequences of Lpp binding Plg are unclear, these results prompt further investigation of the ability of surface exposed Lpp to interact with host molecules such as extracellular matrix components and complement regulators, and the role of these interactions in infections caused by E. coli and other bacteria.
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Affiliation(s)
- Tammy Gonzalez
- Brissette Laboratory, Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks ND, USA
| | - Robert A Gaultney
- Brissette Laboratory, Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks ND, USA
| | - Angela M Floden
- Brissette Laboratory, Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks ND, USA
| | - Catherine A Brissette
- Brissette Laboratory, Department of Basic Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks ND, USA
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Shimada T, Takada H, Yamamoto K, Ishihama A. Expanded roles of two-component response regulator OmpR in Escherichia coli: genomic SELEX search for novel regulation targets. Genes Cells 2015; 20:915-31. [PMID: 26332955 DOI: 10.1111/gtc.12282] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 07/26/2015] [Indexed: 12/22/2022]
Abstract
The two-component system (TCS) is a sophisticated bacterial signal transduction system for regulation of genome transcription in response to environmental conditions. The EnvZ-OmpR system is one of the well-characterized TCS of Escherichia coli, responding to changes in environmental osmolality. Regulation has largely focused on the differential expression of two porins, OmpF and OmpC, which transport small molecules across the outer membrane. Recently, it has become apparent that OmpR serves a more global regulatory role and regulates additional targets. To identify the entire set of regulatory targets of OmpR, we performed the genomic SELEX screening of OmpR-binding sites along the E. coli genome. As a result, more than 30 novel genes have been identified to be under the direct control of OmpR. One abundant group includes the genes encoding a variety of membrane-associated transporters that mediate uptake or efflux of small molecules, while another group encodes a set of transcription regulators, raising a concept that OmpR is poised to control a diverse set of responses by altering downstream transcriptional regulators.
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Affiliation(s)
- Tomohiro Shimada
- Micro-Nano Technology Research Center, Hosei University, Koganai, Tokyo, 184-8584, Japan.,Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuda, Yokohama, 226-8503, Japan
| | - Hiraku Takada
- Micro-Nano Technology Research Center, Hosei University, Koganai, Tokyo, 184-8584, Japan
| | - Kaneyoshi Yamamoto
- Micro-Nano Technology Research Center, Hosei University, Koganai, Tokyo, 184-8584, Japan.,Department of Frontier Bioscience, Hosei University, Koganai, Tokyo, 184-8584, Japan
| | - Akira Ishihama
- Micro-Nano Technology Research Center, Hosei University, Koganai, Tokyo, 184-8584, Japan.,Department of Frontier Bioscience, Hosei University, Koganai, Tokyo, 184-8584, Japan
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Key Residues of Outer Membrane Protein OprI Involved in Hexamer Formation and Bacterial Susceptibility to Cationic Antimicrobial Peptides. Antimicrob Agents Chemother 2015; 59:6210-22. [PMID: 26248382 DOI: 10.1128/aac.01406-15] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 07/17/2015] [Indexed: 11/20/2022] Open
Abstract
Antimicrobial peptides (AMPs) are important components of the host innate defense mechanism against invading pathogens. Our previous studies have shown that the outer membrane protein, OprI from Pseudomonas aeruginosa or its homologue, plays a vital role in the susceptibility of Gram-negative bacteria to cationic α-helical AMPs (Y. M. Lin, S. J. Wu, T. W. Chang, C. F. Wang, C. S. Suen, M. J. Hwang, M. D. Chang, Y. T. Chen, Y. D. Liao, J Biol Chem 285:8985-8994, 2010, http://dx.doi.org/10.1074/jbc.M109.078725; T. W. Chang, Y. M. Lin, C. F. Wang, Y. D. Liao, J Biol Chem 287:418-428, 2012, http://dx.doi.org/10.1074/jbc.M111.290361). Here, we obtained two forms of recombinant OprI: rOprI-F, a hexamer composed of three disulfide-bridged dimers, was active in AMP binding, while rOprI-R, a trimer, was not. All the subunits predominantly consisted of α-helices and exhibited rigid structures with a melting point centered around 76°C. Interestingly, OprI tagged with Escherichia coli signal peptide was expressed in a hexamer, which was anchored on the surface of E. coli, possibly through lipid acids added at the N terminus of OprI and involved in the binding and susceptibility to AMP as native P. aeruginosa OprI. Deletion and mutation studies showed that Cys1 and Asp27 played a key role in hexamer formation and AMP binding, respectively. The increase of OprI hydrophobicity upon AMP binding revealed that it undergoes conformational changes for membrane fusion. Our results showed that OprI on bacterial surfaces is responsible for the recruitment and susceptibility to amphipathic α-helical AMPs and may be used to screen antimicrobials.
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69
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Michel LV, Shaw J, MacPherson V, Barnard D, Bettinger J, D'Arcy B, Surendran N, Hellman J, Pichichero ME. Dual orientation of the outer membrane lipoprotein Pal in Escherichia coli. MICROBIOLOGY-SGM 2015; 161:1251-9. [PMID: 25808171 DOI: 10.1099/mic.0.000084] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Peptidoglycan associated lipoprotein (Pal) of Escherichia coli (E. coli) is a characteristic bacterial lipoprotein, with an N-terminal lipid moiety anchoring it to the outer membrane. Since its discovery over three decades ago, Pal has been well studied for its participation in the Tol-Pal complex which spans the periplasm and has been proposed to play important roles in bacterial survival, pathogenesis and virulence. Previous studies of Pal place the lipoprotein in the periplasm of E. coli, allowing it to interact with Tol proteins and the peptidoglycan layer. Here, we describe for the first time, a subpopulation of Pal which is present on the cell surface of E. coli. Flow cytometry and confocal microscopy detect anti-Pal antibodies on the surface of intact E. coli cells. Interestingly, Pal is surface exposed in an 'all or nothing' manner, such that most of the cells contain only internal Pal, with fewer cells ( < 20 %) exhibiting surface Pal.
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Affiliation(s)
- Lea Vacca Michel
- 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA
| | - Juliana Shaw
- 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA
| | - Victoria MacPherson
- 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA
| | - David Barnard
- 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA
| | - John Bettinger
- 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA
| | - Brooke D'Arcy
- 1School of Chemistry and Materials Science, Rochester Institute of Technology, 85 Lomb Memorial Drive, Rochester, NY, 14623, USA
| | - Naveen Surendran
- 2Rochester General Hospital Research Institute, 1425 Portland Avenue, Rochester, NY 14621, USA
| | - Judith Hellman
- 3Department of Anesthesia and Perioperative Care, University of California, San Francisco, 521 Parnassus Avenue, San Francisco, CA, 94143, USA
| | - Michael E Pichichero
- 2Rochester General Hospital Research Institute, 1425 Portland Avenue, Rochester, NY 14621, USA
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Revisiting the Gram-negative lipoprotein paradigm. J Bacteriol 2015; 197:1705-15. [PMID: 25755189 DOI: 10.1128/jb.02414-14] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Accepted: 03/02/2015] [Indexed: 12/27/2022] Open
Abstract
UNLABELLED The processing of lipoproteins (Lpps) in Gram-negative bacteria is generally considered an essential pathway. Mature lipoproteins in these bacteria are triacylated, with the final fatty acid addition performed by Lnt, an apolipoprotein N-acyltransferase. The mature lipoproteins are then sorted by the Lol system, with most Lpps inserted into the outer membrane (OM). We demonstrate here that the lnt gene is not essential to the Gram-negative pathogen Francisella tularensis subsp. tularensis strain Schu or to the live vaccine strain LVS. An LVS Δlnt mutant has a small-colony phenotype on sucrose medium and increased susceptibility to globomycin and rifampin. We provide data indicating that the OM lipoprotein Tul4A (LpnA) is diacylated but that it, and its paralog Tul4B (LpnB), still sort to the OM in the Δlnt mutant. We present a model in which the Lol sorting pathway of Francisella has a modified ABC transporter system that is capable of recognizing and sorting both triacylated and diacylated lipoproteins, and we show that this modified system is present in many other Gram-negative bacteria. We examined this model using Neisseria gonorrhoeae, which has the same Lol architecture as that of Francisella, and found that the lnt gene is not essential in this organism. This work suggests that Gram-negative bacteria fall into two groups, one in which full lipoprotein processing is essential and one in which the final acylation step is not essential, potentially due to the ability of the Lol sorting pathway in these bacteria to sort immature apolipoproteins to the OM. IMPORTANCE This paper describes the novel finding that the final stage in lipoprotein processing (normally considered an essential process) is not required by Francisella tularensis or Neisseria gonorrhoeae. The paper provides a potential reason for this and shows that it may be widespread in other Gram-negative bacteria.
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71
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Schwechheimer C, Rodriguez DL, Kuehn MJ. NlpI-mediated modulation of outer membrane vesicle production through peptidoglycan dynamics in Escherichia coli. Microbiologyopen 2015; 4:375-89. [PMID: 25755088 PMCID: PMC4475382 DOI: 10.1002/mbo3.244] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 12/10/2014] [Accepted: 01/29/2015] [Indexed: 12/22/2022] Open
Abstract
Outer membrane vesicles (OMVs) are ubiquitously secreted from the outer membrane (OM) of Gram-negative bacteria. These heterogeneous structures are composed of OM filled with periplasmic content from the site of budding. By analyzing mutants that have vesicle production phenotypes, we can gain insight into the mechanism of OMV budding in wild-type cells, which has thus far remained elusive. In this study, we present data demonstrating that the hypervesiculation phenotype of the nlpI deletion mutant of Escherichia coli correlates with changes in peptidoglycan (PG) dynamics. Our data indicate that in stationary phase cultures the nlpI mutant exhibits increased PG synthesis that is dependent on spr, consistent with a model in which NlpI controls the activity of the PG endopeptidase Spr. In log phase, the nlpI mutation was suppressed by a dacB mutation, suggesting that NlpI regulates penicillin-binding protein 4 (PBP4) during exponential growth. The data support a model in which NlpI negatively regulates PBP4 activity during log phase, and Spr activity during stationary phase, and that in the absence of NlpI, the cell survives by increasing PG synthesis. Further, the nlpI mutant exhibited a significant decrease in covalent outer membrane (OM-PG) envelope stabilizing cross-links, consistent with its high level of OMV production. Based on these results, we propose that one mechanism wild-type Gram-negative bacteria can use to modulate vesiculation is by altering PG-OM cross-linking via localized modulation of PG degradation and synthesis.
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Affiliation(s)
- Carmen Schwechheimer
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, 27710
| | - Daniel L Rodriguez
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, 27710
| | - Meta J Kuehn
- Department of Biochemistry, Duke University Medical Center, Durham, North Carolina, 27710
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72
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Buddelmeijer N. The molecular mechanism of bacterial lipoprotein modification—How, when and why? FEMS Microbiol Rev 2015; 39:246-61. [DOI: 10.1093/femsre/fuu006] [Citation(s) in RCA: 89] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Cho SH, Szewczyk J, Pesavento C, Zietek M, Banzhaf M, Roszczenko P, Asmar A, Laloux G, Hov AK, Leverrier P, Van der Henst C, Vertommen D, Typas A, Collet JF. Detecting envelope stress by monitoring β-barrel assembly. Cell 2015; 159:1652-64. [PMID: 25525882 DOI: 10.1016/j.cell.2014.11.045] [Citation(s) in RCA: 129] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 10/06/2014] [Accepted: 11/24/2014] [Indexed: 01/29/2023]
Abstract
The cell envelope protects bacteria from their surroundings. Defects in its integrity or assembly are sensed by signal transduction systems, allowing cells to rapidly adjust. The Rcs phosphorelay responds to outer membrane (OM)- and peptidoglycan-related stress in enterobacteria. We elucidated how the OM lipoprotein RcsF, the upstream Rcs component, senses envelope stress and activates the signaling cascade. RcsF interacts with BamA, the major component of the β-barrel assembly machinery. In growing cells, BamA continuously funnels RcsF through the β-barrel OmpA, displaying RcsF on the cell surface. This process spatially separates RcsF from the downstream Rcs component, which we show is the inner membrane protein IgaA. The Rcs system is activated when BamA fails to bind RcsF and funnel it to OmpA. Newly synthesized RcsF then remains periplasmic, interacting with IgaA to activate the cascade. Thus RcsF senses envelope damage by monitoring the activity of the Bam machinery.
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Affiliation(s)
- Seung-Hyun Cho
- WELBIO, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium; de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Joanna Szewczyk
- WELBIO, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium; de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Christina Pesavento
- European Molecular Biology Laboratory, Genome Biology Unit, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Matylda Zietek
- European Molecular Biology Laboratory, Genome Biology Unit, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Manuel Banzhaf
- European Molecular Biology Laboratory, Genome Biology Unit, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Paula Roszczenko
- WELBIO, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium; de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Abir Asmar
- WELBIO, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium; de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Géraldine Laloux
- de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Ann-Kristin Hov
- European Molecular Biology Laboratory, Genome Biology Unit, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Pauline Leverrier
- de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Charles Van der Henst
- WELBIO, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium; de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Didier Vertommen
- de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium
| | - Athanasios Typas
- European Molecular Biology Laboratory, Genome Biology Unit, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
| | - Jean-François Collet
- WELBIO, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium; de Duve Institute, Université catholique de Louvain, Avenue Hippocrate 75, Brussels 1200, Belgium.
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Abstract
The outer membrane (OM) is the front line of leptospiral interactions with their environment and the mammalian host. Unlike most invasive spirochetes, pathogenic leptospires must be able to survive in both free-living and host-adapted states. As organisms move from one set of environmental conditions to another, the OM must cope with a series of conflicting challenges. For example, the OM must be porous enough to allow nutrient uptake, yet robust enough to defend the cell against noxious substances. In the host, the OM presents a surface decorated with adhesins and receptors for attaching to, and acquiring, desirable host molecules such as the complement regulator, Factor H.Factor H. On the other hand, the OM must enable leptospires to evade detection by the host's immune system on their way from sites of invasion through the bloodstream to the protected niche of the proximal tubule. The picture that is emerging of the leptospiral OM is that, while it shares many of the characteristics of the OMs of spirochetes and Gram-negative bacteria, it is also unique and different in ways that make it of general interest to microbiologists. For example, unlike most other pathogenic spirochetes, the leptospiral OM is rich in lipopolysaccharide (LPS). Leptospiral LPS is similar to that of Gram-negative bacteria but has a number of unique structural features that may explain why it is not recognized by the LPS-specific Toll-like receptor 4 of humans. As in other spirochetes, lipoproteins are major components of the leptospiral OM, though their roles are poorly understood. The functions of transmembrane outer membrane proteins (OMPs) in many cases are better understood, thanks to homologies with their Gram-negative counterparts and the emergence of improved genetic techniques. This chapter will review recent discoveries involving the leptospiral OM and its role in leptospiral physiology and pathogenesis.
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Affiliation(s)
- David A Haake
- Division of Infectious Diseases, VA Greater Los Angeles Healthcare System, Los Angeles, CA, 90073, USA,
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75
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Schwechheimer C, Kulp A, Kuehn MJ. Modulation of bacterial outer membrane vesicle production by envelope structure and content. BMC Microbiol 2014; 14:324. [PMID: 25528573 PMCID: PMC4302634 DOI: 10.1186/s12866-014-0324-1] [Citation(s) in RCA: 115] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Accepted: 12/11/2014] [Indexed: 02/14/2023] Open
Abstract
Background Vesiculation is a ubiquitous secretion process of Gram-negative bacteria, where outer membrane vesicles (OMVs) are small spherical particles on the order of 50 to 250 nm composed of outer membrane (OM) and lumenal periplasmic content. Vesicle functions have been elucidated in some detail, showing their importance in virulence factor secretion, bacterial survival, and biofilm formation in pathogenesis. Furthermore, OMVs serve as an envelope stress response, protecting the secreting bacteria from internal protein misfolding stress, as well as external envelope stressors. Despite their important functional roles very little is known about the regulation and mechanism of vesicle production. Based on the envelope architecture and prior characterization of the hypervesiculation phenotypes for mutants lacking the lipoprotein, Lpp, which is involved in the covalent OM-peptidoglycan (PG) crosslinks, it is expected that an inverse relationship exists between OMV production and PG-crosslinked Lpp. Results In this study, we found that subtle modifications of PG remodeling and crosslinking modulate OMV production, inversely correlating with bound Lpp levels. However, this inverse relationship was not found in strains in which OMV production is driven by an increase in “periplasmic pressure” resulting from the accumulation of protein, PG fragments, or lipopolysaccharide. In addition, the characterization of an nlpA deletion in backgrounds lacking either Lpp- or OmpA-mediated envelope crosslinks demonstrated a novel role for NlpA in envelope architecture. Conclusions From this work, we conclude that OMV production can be driven by distinct Lpp concentration-dependent and Lpp concentration-independent pathways. Electronic supplementary material The online version of this article (doi:10.1186/s12866-014-0324-1) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Carmen Schwechheimer
- Department of Biochemistry, Duke University Medical Center, Durham, NC, 27710, USA.
| | - Adam Kulp
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC, 27710, USA.
| | - Meta J Kuehn
- Department of Biochemistry, Duke University Medical Center, Durham, NC, 27710, USA.
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Konovalova A, Perlman DH, Cowles CE, Silhavy TJ. Transmembrane domain of surface-exposed outer membrane lipoprotein RcsF is threaded through the lumen of β-barrel proteins. Proc Natl Acad Sci U S A 2014; 111:E4350-8. [PMID: 25267629 PMCID: PMC4205638 DOI: 10.1073/pnas.1417138111] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
RcsF (regulator of capsule synthesis) is an outer membrane (OM) lipoprotein that functions to sense defects such as changes in LPS. However, LPS is found in the outer leaflet, and RcsF was thought to be tethered to the inner leaflet by its lipidated N terminus, raising the question of how it monitors LPS. We show that RcsF has a transmembrane topology with the lipidated N terminus on the cell surface and the C-terminal signaling domain in the periplasm. Strikingly, the short, unstructured, charged transmembrane domain is threaded through the lumen of β-barrel OM proteins where it is protected from the hydrophobic membrane interior. We present evidence that these unusual complexes, which contain one protein inside another, are formed by the Bam complex that assembles all β-barrel proteins in the OM. The ability of the Bam complex to expose lipoproteins at the cell surface underscores the mechanistic versatility of the β-barrel assembly machine.
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Affiliation(s)
- Anna Konovalova
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ 08544
| | - David H Perlman
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ 08544
| | - Charles E Cowles
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ 08544
| | - Thomas J Silhavy
- Department of Molecular Biology, Lewis Thomas Laboratory, Princeton University, Princeton, NJ 08544
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77
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Orfanoudaki G, Economou A. Proteome-wide subcellular topologies of E. coli polypeptides database (STEPdb). Mol Cell Proteomics 2014; 13:3674-87. [PMID: 25210196 DOI: 10.1074/mcp.o114.041137] [Citation(s) in RCA: 54] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Cell compartmentalization serves both the isolation and the specialization of cell functions. After synthesis in the cytoplasm, over a third of all proteins are targeted to other subcellular compartments. Knowing how proteins are distributed within the cell and how they interact is a prerequisite for understanding it as a whole. Surface and secreted proteins are important pathogenicity determinants. Here we present the STEP database (STEPdb) that contains a comprehensive characterization of subcellular localization and topology of the complete proteome of Escherichia coli. Two widely used E. coli proteomes (K-12 and BL21) are presented organized into thirteen subcellular classes. STEPdb exploits the wealth of genetic, proteomic, biochemical, and functional information on protein localization, secretion, and targeting in E. coli, one of the best understood model organisms. Subcellular annotations were derived from a combination of bioinformatics prediction, proteomic, biochemical, functional, topological data and extensive literature re-examination that were refined through manual curation. Strong experimental support for the location of 1553 out of 4303 proteins was based on 426 articles and some experimental indications for another 526. Annotations were provided for another 320 proteins based on firm bioinformatic predictions. STEPdb is the first database that contains an extensive set of peripheral IM proteins (PIM proteins) and includes their graphical visualization into complexes, cellular functions, and interactions. It also summarizes all currently known protein export machineries of E. coli K-12 and pairs them, where available, with the secretory proteins that use them. It catalogs the Sec- and TAT-utilizing secretomes and summarizes their topological features such as signal peptides and transmembrane regions, transmembrane topologies and orientations. It also catalogs physicochemical and structural features that influence topology such as abundance, solubility, disorder, heat resistance, and structural domain families. Finally, STEPdb incorporates prediction tools for topology (TMHMM, SignalP, and Phobius) and disorder (IUPred) and implements the BLAST2STEP that performs protein homology searches against the STEPdb.
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Affiliation(s)
- Georgia Orfanoudaki
- From the ‡Institute of Molecular Biology and Biotechnology-FoRTH and §Department of Biology-University of Crete, P.O. Box 1385, Iraklio, Crete, Greece
| | - Anastassios Economou
- From the ‡Institute of Molecular Biology and Biotechnology-FoRTH and §Department of Biology-University of Crete, P.O. Box 1385, Iraklio, Crete, Greece; ¶Laboratory of Molecular Bacteriology; Rega Institute, Department of Microbiology and Immunology, KU Leuven, Herrestraat 49, B-3000 Leuven, Belgium
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Guo MS, Updegrove TB, Gogol EB, Shabalina SA, Gross CA, Storz G. MicL, a new σE-dependent sRNA, combats envelope stress by repressing synthesis of Lpp, the major outer membrane lipoprotein. Genes Dev 2014; 28:1620-34. [PMID: 25030700 PMCID: PMC4102768 DOI: 10.1101/gad.243485.114] [Citation(s) in RCA: 175] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
In enteric bacteria, the transcription factor σE maintains membrane homeostasis by inducing the synthesis of membrane repair proteins as well as two small regulatory RNAs (sRNAs) that down-regulate membrane porin synthesis. Here, Storz and colleagues identify a third σE-dependent sRNA, MicL, transcribed from the cutC gene coding sequence. MicL represses the outer membrane lipoprotein Lpp and is responsible for the copper sensitivity phenotype previously associated with cutC loss. This discovery is critical to understanding the networks that control outer membrane homeostasis in response to stress. In enteric bacteria, the transcription factor σE maintains membrane homeostasis by inducing synthesis of proteins involved in membrane repair and two small regulatory RNAs (sRNAs) that down-regulate synthesis of abundant membrane porins. Here, we describe the discovery of a third σE-dependent sRNA, MicL (mRNA-interfering complementary RNA regulator of Lpp), transcribed from a promoter located within the coding sequence of the cutC gene. MicL is synthesized as a 308-nucleotide (nt) primary transcript that is processed to an 80-nt form. Both forms possess features typical of Hfq-binding sRNAs but surprisingly target only a single mRNA, which encodes the outer membrane lipoprotein Lpp, the most abundant protein of the cell. We show that the copper sensitivity phenotype previously ascribed to inactivation of the cutC gene is actually derived from the loss of MicL and elevated Lpp levels. This observation raises the possibility that other phenotypes currently attributed to protein defects are due to deficiencies in unappreciated regulatory RNAs. We also report that σE activity is sensitive to Lpp abundance and that MicL and Lpp comprise a new σE regulatory loop that opposes membrane stress. Together MicA, RybB, and MicL allow σE to repress the synthesis of all abundant outer membrane proteins in response to stress.
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Affiliation(s)
- Monica S Guo
- Department of Microbiology and Immunology, University of California at San Francisco, San Francisco, California 94158, USA
| | - Taylor B Updegrove
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Emily B Gogol
- Department of Microbiology and Immunology, University of California at San Francisco, San Francisco, California 94158, USA
| | - Svetlana A Shabalina
- National Center for Biotechnology Information, National Institutes of Health, Bethesda, Maryland 20894, USA
| | - Carol A Gross
- Department of Microbiology and Immunology, University of California at San Francisco, San Francisco, California 94158, USA
| | - Gisela Storz
- Cell Biology and Metabolism Program, Eunice Kennedy Shriver National Institutes of Health, Bethesda, Maryland 20892, USA
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79
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Hernández SB, Cava F, Pucciarelli MG, García-Del Portillo F, de Pedro MA, Casadesús J. Bile-induced peptidoglycan remodelling in Salmonella enterica. Environ Microbiol 2014; 17:1081-9. [PMID: 24762004 DOI: 10.1111/1462-2920.12491] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 04/11/2014] [Accepted: 04/20/2014] [Indexed: 02/02/2023]
Abstract
Changes in the peptidoglycan (PG) structure of Salmonella enterica are detected in the presence of a sublethal concentration of sodium deoxycholate (DOC): (i) lower proportions of Braun lipoprotein (Lpp)-bound muropeptides; (ii) reduced levels of muropeptides cross-linked by L(meso)-diaminopimelyl-D(meso)-diaminopimelic acid (L-D) peptide bridges (3-3 cross-links). Similar structural changes are found in S. enterica cultures adapted to grow in the presence of a lethal concentration of DOC, suggesting that reduced anchoring of Braun protein to PG and low occurrence of 3-3 cross-links may increase S. enterica resistance to bile. This view is further supported by additional observations: (i) A triple mutant lacking L,D-transpeptidases YbiS, ErfK, and YcfS, which does not contain Lpp anchored to PG, is hyper-resistant to bile; (ii) enhanced 3-3 cross-linking upon overexpression of YnhG transpeptidase causes a decrease in bile resistance. These observations suggest that remodelling of the cell wall may be added to the list of adaptive responses that permit survival of S. enterica in the presence of bile.
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Affiliation(s)
- Sara B Hernández
- Facultad de Biología, Departamento de Genética, Universidad de Sevilla, Apartado 1095, 41080, Sevilla, Spain
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80
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Secretion of bacterial lipoproteins: through the cytoplasmic membrane, the periplasm and beyond. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:1509-16. [PMID: 24780125 DOI: 10.1016/j.bbamcr.2014.04.022] [Citation(s) in RCA: 150] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 04/16/2014] [Accepted: 04/18/2014] [Indexed: 11/20/2022]
Abstract
Bacterial lipoproteins are peripherally anchored membrane proteins that play a variety of roles in bacterial physiology and virulence in monoderm (single membrane-enveloped, e.g., gram-positive) and diderm (double membrane-enveloped, e.g., gram-negative) bacteria. After export of prolipoproteins through the cytoplasmic membrane, which occurs predominantly but not exclusively via the general secretory or Sec pathway, the proteins are lipid-modified at the cytoplasmic membrane in a multistep process that involves sequential modification of a cysteine residue and cleavage of the signal peptide by the signal II peptidase Lsp. In both monoderms and diderms, signal peptide processing is preceded by acylation with a diacylglycerol through preprolipoprotein diacylglycerol transferase (Lgt). In diderms but also some monoderms, lipoproteins are further modified with a third acyl chain through lipoprotein N-acyl transferase (Lnt). Fully modified lipoproteins that are destined to be anchored in the inner leaflet of the outer membrane (OM) are selected, transported and inserted by the Lol (lipoprotein outer membrane localization) pathway machinery, which consists of the inner-membrane (IM) ABC transporter-like LolCDE complex, the periplasmic LolA chaperone and the OM LolB lipoprotein receptor. Retention of lipoproteins in the cytoplasmic membrane results from Lol avoidance signals that were originally described as the "+2 rule". Surface localization of lipoproteins in diderms is rare in most bacteria, with the exception of several spirochetal species. Type 2 (T2SS) and type 5 (T5SS) secretion systems are involved in secretion of specific surface lipoproteins of γ-proteobacteria. In the model spirochete Borrelia burgdorferi, surface lipoprotein secretion does not follow established sorting rules, but remains dependent on N-terminal peptide sequences. Secretion through the outer membrane requires maintenance of lipoproteins in a translocation-competent unfolded conformation, likely through interaction with a periplasmic holding chaperone, which delivers the proteins to an outer membrane lipoprotein flippase. This article is part of a Special Issue entitled: Protein trafficking and secretion in bacteria. Guest Editors: Anastassios Economou and Ross Dalbey.
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81
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Characterization of the Vibrio cholerae VolA surface-exposed lipoprotein lysophospholipase. J Bacteriol 2014; 196:1619-26. [PMID: 24532770 DOI: 10.1128/jb.01281-13] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bacterial lipases play important roles in bacterial metabolism and environmental response. Our laboratory recently discovered that a novel lipoprotein lysophospholipase, VolA, localizes on the surface of the Gram-negative aquatic pathogen Vibrio cholerae. VolA functions to cleave exogenous lysophosphatidylcholine, freeing the fatty acid moiety for use by V. cholerae. This fatty acid is transported into the cell and can be used as a nutrient and, more importantly, as a way to alter the membrane architecture via incorporation into the phospholipid biosynthesis pathway. There are few examples of Gram-negative, surface-exposed lipoproteins, and VolA is unique, as it has a previously undercharacterized function in V. cholerae membrane remodeling. Herein, we report the biochemical characterization of VolA. We show that VolA is a canonical lipoprotein via mass spectrometry analysis and demonstrate the in vitro activity of VolA under a variety of conditions. Additionally, we show that VolA contains a conserved Gly-Xaa-Ser-Xaa-Gly motif typical of lipases. Interestingly, we report the observation of VolA homologs in other aquatic pathogens. An Aeromonas hydrophila VolA homolog complements a V. cholerae VolA mutant in growth on lysophosphatidylcholine as the sole carbon source and in enzymatic assays. These results support the idea that the lipase activity of surface-exposed VolA likely contributes to the success of V. cholerae, improving the overall adaptation and survival of the organism in different environments.
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82
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Salinity-dependent impacts of ProQ, Prc, and Spr deficiencies on Escherichia coli cell structure. J Bacteriol 2014; 196:1286-96. [PMID: 24443528 DOI: 10.1128/jb.00827-13] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
ProQ is a cytoplasmic protein with RNA chaperone activities that reside in FinO- and Hfq-like domains. Lesions at proQ decrease the level of the osmoregulatory glycine betaine transporter ProP. Lesions at proQ eliminated ProQ and Prc, the periplasmic protease encoded by the downstream gene prc. They dramatically slowed the growth of Escherichia coli populations and altered the morphologies of E. coli cells in high-salinity medium. ProQ and Prc deficiencies were associated with different phenotypes. ProQ-deficient bacteria were elongated unless glycine betaine was provided. High-salinity cultures of Prc-deficient bacteria included spherical cells with an enlarged periplasm and an eccentric nucleoid. The nucleoid-containing compartment was bounded by the cytoplasmic membrane and peptidoglycan. This phenotype was not evident in bacteria cultivated at low or moderate salinity, nor was it associated with murein lipoprotein (Lpp) deficiency, and it differed from those elicited by the MreB inhibitor A-22 or the FtsI inhibitor aztreonam at low or high salinity. It was suppressed by deletion of spr, which encodes one of three murein hydrolases that are redundantly essential for enlargement of the murein sacculus. Prc deficiency may alter bacterial morphology by impairing control of Spr activity at high salinity. ProQ and Prc deficiencies lowered the ProP activity of bacteria cultivated at moderate salinity by approximately 70% and 30%, respectively, but did not affect other osmoregulatory functions. The effects of ProQ and Prc deficiencies on ProP activity are indirect, reflecting their roles in the maintenance of cell structure.
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83
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Genetic redundancy, proximity, and functionality of lspA, the target of antibiotic TA, in the Myxococcus xanthus producer strain. J Bacteriol 2014; 196:1174-83. [PMID: 24391051 DOI: 10.1128/jb.01361-13] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We recently showed that type II signal peptidase (SPaseII) encoded by lspA is the target of an antibiotic called TA (myxovirescin), which is made by Myxococcus xanthus. SPaseII cleaves the signal peptide during bacterial lipoprotein processing. Bacteria typically contain one lspA gene; however, strikingly, the M. xanthus DK1622 genome contains four (lspA1 to lspA4). Since two of these genes, lspA3 and lspA4, are located in the giant TA biosynthetic gene cluster, we hypothesized they may play a role in TA resistance. To investigate the functions of the four M. xanthus lspA (lspA(Mx)) genes, we conducted sequence comparisons and found that they contained nearly all the conserved residues characteristic of SPaseII family members. Genetic studies found that an Escherichia coli ΔlspA mutation could be complemented by any of the lspA(Mx) genes in an lpp mutant background, but not in an E. coli lpp(+) background. Because Lpp is the most abundant E. coli lipoprotein, these results suggest the M. xanthus proteins do not function as efficiently as the host enzyme. In E. coli, overexpression of each of the LspA(Mx) proteins conferred TA and globomycin resistance, although LspA3 conferred the highest degree of resistance. In M. xanthus, each lspA(Mx) gene could be deleted and was therefore dispensable for growth. However, lspA3 or lspA4 deletion mutants each exhibited a tan phase variation bias, which likely accounts for their reduced-swarming and delayed-development phenotypes. In summary, we propose that all four LspA(Mx) proteins function as SPaseIIs and that LspA3 and LspA4 might also have roles in TA resistance and regulation, respectively.
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84
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Enteric YaiW is a surface-exposed outer membrane lipoprotein that affects sensitivity to an antimicrobial peptide. J Bacteriol 2013; 196:436-44. [PMID: 24214946 DOI: 10.1128/jb.01179-13] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
yaiW is a previously uncharacterized gene found in enteric bacteria that is of particular interest because it is located adjacent to the sbmA gene, whose bacA ortholog is required for Sinorhizobium meliloti symbiosis and Brucella abortus pathogenesis. We show that yaiW is cotranscribed with sbmA in Escherichia coli and Salmonella enterica serovar Typhi and Typhimurium strains. We present evidence that the YaiW is a palmitate-modified surface exposed outer membrane lipoprotein. Since BacA function affects the very-long-chain fatty acid (VLCFA) modification of S. meliloti and B. abortus lipid A, we tested whether SbmA function might affect either the fatty acid modification of the YaiW lipoprotein or the fatty acid modification of enteric lipid A but found that it did not. Interestingly, we did observe that E. coli SbmA suppresses deficiencies in the VLCFA modification of the lipopolysaccharide of an S. meliloti bacA mutant despite the absence of VLCFA in E. coli. Finally, we found that both YaiW and SbmA positively affect the uptake of proline-rich Bac7 peptides, suggesting a possible connection between their cellular functions.
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85
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Synthetic effect between envelope stress and lack of outer membrane vesicle production in Escherichia coli. J Bacteriol 2013; 195:4161-73. [PMID: 23852867 DOI: 10.1128/jb.02192-12] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Outer membrane vesicles (OMVs) are composed of outer membrane and periplasmic components and are ubiquitously secreted by Gram-negative bacteria. OMVs can disseminate virulence factors for pathogenic bacteria as well as serve as an envelope stress response. From a transposon mutant screen for OMV phenotypes, it was discovered that an nlpA mutant of Escherichia coli produces fewer OMVs than the wild type, whereas a degP mutant produces higher levels of OMVs. NlpA is an inner-membrane-anchored lipoprotein that has a minor role in methionine import. DegP is a periplasmic chaperone/protease for misfolded envelope proteins that is critical when cells are heat shocked. To reveal how these proteins contribute to OMV production, the mutations were combined and the double mutant analyzed. The ΔnlpA ΔdegP strain displayed a high-temperature growth defect that corresponded to the production of fewer OMVs than produced by the ΔdegP strain. This phenotype also pertained to other undervesiculation mutations in a ΔdegP background. The hypovesiculation phenotype of ΔnlpA in the wild-type strain as well as in the degP deletion strain was found to be a stationary-phase phenomenon. The periplasm of the ΔnlpA ΔdegP strain was determined to contain significantly more protein in stationary phase than the wild type. Additionally, misfolded DegP substrate outer membrane porins were detected in ΔdegP mutant-derived OMVs. These data suggest that an accumulation of envelope proteins resulting from decreased vesiculation was toxic and contributed to the growth defect. We conclude that OMV production contributes to relieve the envelope of accumulated toxic proteins and that NlpA plays an important role in the production of vesicles in stationary phase.
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86
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Sanders AN, Pavelka MS. Phenotypic analysis of Eschericia coli mutants lacking L,D-transpeptidases. MICROBIOLOGY-SGM 2013; 159:1842-1852. [PMID: 23832002 DOI: 10.1099/mic.0.069211-0] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Escherichia coli has five genes encoding L,D-transpeptidases (Ldt) with varied functions. Three of these enzymes (YbiS, ErfK, YcfS) have been shown to cross-link Braun's lipoprotein to the peptidoglycan (PG), while the other two (YnhG, YcbB) form direct meso-diaminopimelate (DAP-DAP, or 3-3) cross-links within the PG. In addition, Ldt enzymes can also incorporate non-canonical D-amino acids, such as D-methionine, into the PG. To further investigate the role of these enzymes and, in particular, 3-3 linkages in cell envelope physiology we constructed and phenotypically characterized a variety of multiple Ldt deletion mutants of E. coli. We report that a triple deletion mutant lacking ybiS, erfK and ycfS is hypersusceptible to the metal-chelating agent EDTA, leaks periplasmic proteins and is resistant to the toxic effect of D-methionine. A double ynhG ycbB mutant had no discernible phenotype; however, examination of the phenotypes of various Ldt mutants bearing an additional DAP auxotrophic mutation (dapA : : Cm) showed that a quintuple mutant strain lacking all Ldt genes was severely impaired for growth on media with limited DAP. These data demonstrate that loss of the E. coli Ldt enzymes involved with coupling the PG to Braun's lipoprotein resulted in the loss of outer membrane stability while loss of the Ldt enzymes involved with DAP-DAP linkages had no observable effect on the cell envelope. Loss of all Ldt enzymes proved detrimental to growth when cells were starved for DAP, indicating a combined role for both 3-3 and Braun's lipoprotein cross-links in cell viability only under a specific PG stress.
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Affiliation(s)
- Akeisha N Sanders
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA
| | - Martin S Pavelka
- Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, NY 14642, USA
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87
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Michel LV, Snyder J, Schmidt R, Milillo J, Grimaldi K, Kalmeta B, Khan MN, Sharma S, Wright LK, Pichichero ME. Dual orientation of the outer membrane lipoprotein P6 of nontypeable haemophilus influenzae. J Bacteriol 2013; 195:3252-9. [PMID: 23687267 PMCID: PMC3697637 DOI: 10.1128/jb.00185-13] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 05/12/2013] [Indexed: 11/20/2022] Open
Abstract
The majority of outer membrane (OM) lipoproteins in Gram-negative bacteria are tethered to the membrane via an attached lipid moiety and oriented facing in toward the periplasmic space; a few lipoproteins have been shown to be surface exposed. The outer membrane lipoprotein P6 from the Gram-negative pathogenic bacterium nontypeable Haemophilus influenzae (NTHi) is surface exposed and a leading vaccine candidate for prevention of NTHi infections. However, we recently found that P6 is not a transmembrane protein as previously thought (L. V. Michel, B. Kalmeta, M. McCreary, J. Snyder, P. Craig, M. E. Pichichero, Vaccine 29:1624-1627, 2011). Here we pursued studies to show that P6 has a dual orientation, existing infrequently as surface exposed and predominantly as internally oriented toward the periplasmic space. Flow cytometry using three monoclonal antibodies with specificity for P6 showed surface staining of whole NTHi cells. Confocal microscopy imaging confirmed that antibodies targeted surface-exposed P6 of intact NTHi cells and not internal P6 in membrane-compromised or dead cells. Western blots of two wild-type NTHi strains and a mutant NTHi strain that does not express P6 showed that P6 antibodies do not detect a promiscuous epitope on NTHi. Depletion of targets to nonlipidated P6 significantly decreased bactericidal activity of human serum. Protease digestion of surface-exposed P6 demonstrated that P6 is predominantly internally localized in a manner similar to its homologue Pal in Escherichia coli. We conclude that P6 of NTHi is likely inserted into the OM in two distinct orientations, with the predominant orientation facing in toward the periplasm.
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Affiliation(s)
- Lea Vacca Michel
- School of Chemistry and Materials Science, Rochester Institute of Technology, Rochester, NY, USA.
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88
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Abstract
Previous work from our laboratory showed that the Gram-negative aquatic pathogen Vibrio cholerae can take up a much wider repertoire of fatty acids than other Gram-negative organisms. The current work elaborated on the ability of V. cholerae to exploit an even more diverse pool of lipid nutrients from its environment. We have demonstrated that the bacterium can use lysophosphatidylcholine as a metabolite for growth. Using a combination of thin-layer chromatography and mass spectrometry, we also showed that lysophosphatidylcholine-derived fatty acid moieties can be used for remodeling the V. cholerae membrane architecture. Furthermore, we have identified a lysophospholipase, VolA (Vibrio outer membrane lysophospholipase A), required for these activities. The enzyme is well conserved in Vibrio species, is coexpressed with the outer membrane fatty acid transporter FadL, is one of very few surface-exposed lipoprotein enzymes to be identified in Gram-negative bacteria and the first instance of a surface lipoprotein phospholipase. We propose a model whereby the bacterium efficiently couples the liberation of fatty acid from lysophosphatidylcholine to its subsequent metabolic uptake. An expanded ability to scavenge diverse environmental lipids at the bacterial surface increases overall bacterial fitness and promotes homeoviscous adaptation through membrane remodeling. Our understanding of how bacteria utilize environmental lipid sources has been limited to lipids such as fatty acids and cholesterol. This narrow scope may be attributed to both the intricate nature of lipid uptake mechanisms and the diversity of lipid substrates encountered within an ecological niche. By examining the ability of the pathogen Vibrio cholerae to utilize exogenous lipids, we uncovered a surface-exposed lipoprotein (VolA) that is required for processing the prevalent host lipid lysophosphatidylcholine. VolA functions as a lipase liberating a fatty acid from exogenous lysophospholipids. The freed fatty acid is then transported into the cell, serving as a carbon source, or shunted into phospholipid synthesis for membrane assembly. A limited number of surface-exposed lipoproteins have been found in Gram-negative organisms, and few have enzymatic function. This work highlights the ability of bacteria to exploit exogenous lipids for both maintenance of the membrane and carbon source acquisition.
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89
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Schwechheimer C, Sullivan CJ, Kuehn MJ. Envelope control of outer membrane vesicle production in Gram-negative bacteria. Biochemistry 2013; 52:3031-40. [PMID: 23521754 DOI: 10.1021/bi400164t] [Citation(s) in RCA: 125] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
All Gram-negative bacteria studied to date have been shown to produce outer membrane vesicles (OMVs), which are budded, released spheres of outer membrane with periplasmic content. OMVs have been implicated in the delivery of virulence factors in pathogenesis. However, OMVs also benefit nonpathogenic species by delivering degradative enzymes to defend an ecological niche against competing bacterial species, and they can serve as an envelope stress response. Despite these important roles, very little is known about the mechanism of production of OMVs. Here we review the advantage of vesiculation, particularly in a nonpathogenic context, as well as the hurdles that have to be overcome in Gram-negative envelope architecture before a vesicle can form and bud. Lastly, we address the question of whether OMV production is a stochastic or regulated process.
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Affiliation(s)
- Carmen Schwechheimer
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
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90
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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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91
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Abstract
Bacterial cell division is facilitated by the divisome, a dynamic multiprotein assembly localizing at mid-cell to synthesize the stress-bearing peptidoglycan and to constrict all cell envelope layers. Divisome assembly occurs in two steps and involves multiple interactions between more than 20 essential and accessory cell division proteins. Well before constriction and while the cell is still elongating, the tubulin-like FtsZ and early cell division proteins form a ring-like structure at mid-cell. Cell division starts once certain peptidoglycan enzymes and their activators have moved to the FtsZ-ring. Gram-negative bacteria like Escherichia coli simultaneously synthesize and cleave the septum peptidoglycan during division leading to a constriction. The outer membrane constricts together with the peptidoglycan layer with the help of the transenvelope spanning Tol-Pal system.
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Affiliation(s)
- Alexander J F Egan
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, UK
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92
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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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93
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Helical insertion of peptidoglycan produces chiral ordering of the bacterial cell wall. Proc Natl Acad Sci U S A 2012; 109:E595-604. [PMID: 22343529 DOI: 10.1073/pnas.1117132109] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The regulation of cell shape is a common challenge faced by organisms across all biological kingdoms. In nearly all bacteria, cell shape is determined by the architecture of the peptidoglycan cell wall, a macromolecule consisting of glycan strands crosslinked by peptides. In addition to shape, cell growth must also maintain the wall structural integrity to prevent lysis due to large turgor pressures. Robustness can be accomplished by establishing a globally ordered cell-wall network, although how a bacterium generates and maintains peptidoglycan order on the micron scale using nanometer-sized proteins remains a mystery. Here, we demonstrate that left-handed chirality of the MreB cytoskeleton in the rod-shaped bacterium Escherichia coli gives rise to a global, right-handed chiral ordering of the cell wall. Local, MreB-guided insertion of material into the peptidoglycan network naturally orders the glycan strands and causes cells to twist left-handedly during elongational growth. Through comparison with the right-handed twisting of Bacillus subtilis cells, our work supports a common mechanism linking helical insertion and chiral cell-wall ordering in rod-shaped bacteria. These physical principles of cell growth link the molecular structure of the bacterial cytoskeleton, mechanisms of wall synthesis, and the coordination of cell-wall architecture.
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94
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Abstract
Decrypting the structure, function, and molecular interactions of complex molecular machines in their cellular context and at atomic resolution is of prime importance for understanding fundamental physiological processes. Nuclear magnetic resonance is a well-established imaging method that can visualize cellular entities at the micrometer scale and can be used to obtain 3D atomic structures under in vitro conditions. Here, we introduce a solid-state NMR approach that provides atomic level insights into cell-associated molecular components. By combining dedicated protein production and labeling schemes with tailored solid-state NMR pulse methods, we obtained structural information of a recombinant integral membrane protein and the major endogenous molecular components in a bacterial environment. Our approach permits studying entire cellular compartments as well as cell-associated proteins at the same time and at atomic resolution.
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95
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Yao Y, Barghava N, Kim J, Niederweis M, Marassi FM. Molecular structure and peptidoglycan recognition of Mycobacterium tuberculosis ArfA (Rv0899). J Mol Biol 2011; 416:208-20. [PMID: 22206986 DOI: 10.1016/j.jmb.2011.12.030] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2011] [Revised: 10/30/2011] [Accepted: 12/13/2011] [Indexed: 02/03/2023]
Abstract
Mycobacterium tuberculosis ArfA (Rv0899) is a membrane protein encoded by an operon that is required for supporting bacterial growth in acidic environments. Its C-terminal domain (C domain) shares significant sequence homology with the OmpA-like family of peptidoglycan-binding domains, suggesting that its physiological function in acid stress protection may be related to its interaction with the mycobacterial cell wall. Previously, we showed that ArfA forms three independently structured modules, and we reported the structure of its central domain (B domain). Here, we describe the high-resolution structure and dynamics of the C domain, we identify ArfA as a peptidoglycan-binding protein and we elucidate the molecular basis for its specific recognition of diaminopimelate-type peptidoglycan. The C domain of ArfA adopts the characteristic fold of the OmpA-like family. It exhibits pH-dependent conformational dynamics (with significant heterogeneity at neutral pH and a more ordered structure at acidic pH), which could be related to its acid stress response. The C domain associates tightly with polymeric peptidoglycan isolated from M. tuberculosis and also associates with a soluble peptide intermediate of peptidoglycan biosynthesis. This enabled us to characterize the peptidoglycan binding site where five highly conserved ArfA residues, including two key arginines, establish the specificity for diaminopimelate- but not Lys-type peptidoglycan. ArfA is the first peptidoglycan-binding protein to be identified in M. tuberculosis. Its functions in acid stress protection and peptidoglycan binding suggest a link between the acid stress response and the physicochemical properties of the mycobacterial cell wall.
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Affiliation(s)
- Yong Yao
- Sanford Burnham Medical Research Institute, La Jolla, CA 92037, USA
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96
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Abstract
The review summarizes the abundant information on the 35 identified peptidoglycan (PG) hydrolases of Escherichia coli classified into 12 distinct families, including mainly glycosidases, peptidases, and amidases. An attempt is also made to critically assess their functions in PG maturation, turnover, elongation, septation, and recycling as well as in cell autolysis. There is at least one hydrolytic activity for each bond linking PG components, and most hydrolase genes were identified. Few hydrolases appear to be individually essential. The crystal structures and reaction mechanisms of certain hydrolases having defined functions were investigated. However, our knowledge of the biochemical properties of most hydrolases still remains fragmentary, and that of their cellular functions remains elusive. Owing to redundancy, PG hydrolases far outnumber the enzymes of PG biosynthesis. The presence of the two sets of enzymes acting on the PG bonds raises the question of their functional correlations. It is difficult to understand why E. coli keeps such a large set of PG hydrolases. The subtle differences in substrate specificities between the isoenzymes of each family certainly reflect a variety of as-yet-unidentified physiological functions. Their study will be a far more difficult challenge than that of the steps of the PG biosynthesis pathway.
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Affiliation(s)
- Jean van Heijenoort
- Institut de Biochimie et Biophysique Moléculaire et Cellulaire, Bat 430, Université Paris-Sud, Orsay F-91405, France.
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97
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Chang TW, Lin YM, Wang CF, Liao YD. Outer membrane lipoprotein Lpp is Gram-negative bacterial cell surface receptor for cationic antimicrobial peptides. J Biol Chem 2011; 287:418-428. [PMID: 22084237 DOI: 10.1074/jbc.m111.290361] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Antimicrobial peptides/proteins (AMPs) are important components of the host innate defense mechanisms. Here we demonstrate that the outer membrane lipoprotein, Lpp, of Enterobacteriaceae interacts with and promotes susceptibility to the bactericidal activities of AMPs. The oligomeric Lpp was specifically recognized by several cationic α-helical AMPs, including SMAP-29, CAP-18, and LL-37; AMP-mediated bactericidal activities were blocked by anti-Lpp antibody blocking. Blebbing of the outer membrane and increase in membrane permeability occurred in association with the coordinate internalization of Lpp and AMP. Interestingly, the specific binding of AMP to Lpp was resistant to divalent cations and salts, which were able to inhibit the bactericidal activities of some AMPs. Furthermore, using His-tagged Lpp as a ligand, we retrieved several characterized AMPs, including SMAP-29 and hRNase 7, from a peptide library containing crude mammalian cell lysates. Overall, this study explores a new mechanism and target of antimicrobial activity and provides a novel method for screening of antimicrobials for use against drug-resistant bacteria.
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Affiliation(s)
- Ting-Wei Chang
- Institute of Pharmacology, National Yang-Ming University, Taipei 112, Taiwan; Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan; Program in Molecular Medicine, School of Life Sciences, National Yang-Ming, University, 155 Linong St., Sec. 2, Taipei 112, Taiwan
| | - Yu-Ming Lin
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
| | - Chiu-Feng Wang
- Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan
| | - You-Di Liao
- Institute of Pharmacology, National Yang-Ming University, Taipei 112, Taiwan; Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan; Program in Molecular Medicine, School of Life Sciences, National Yang-Ming, University, 155 Linong St., Sec. 2, Taipei 112, Taiwan.
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98
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Probing the Borrelia burgdorferi surface lipoprotein secretion pathway using a conditionally folding protein domain. J Bacteriol 2011; 193:6724-32. [PMID: 21965569 DOI: 10.1128/jb.06042-11] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Surface lipoproteins of Borrelia spirochetes are important virulence determinants in the transmission and pathogenesis of Lyme disease and relapsing fever. To further define the conformational secretion requirements and to identify potential lipoprotein translocation intermediates associated with the bacterial outer membrane (OM), we generated constructs in which Borrelia burgdorferi outer surface lipoprotein A (OspA) was fused to calmodulin (CaM), a conserved eukaryotic protein undergoing calcium-dependent folding. Protein localization assays showed that constructs in which CaM was fused to full-length wild-type (wt) OspA or to an intact OspA N-terminal "tether" peptide retained their competence for OM translocation even in the presence of calcium. In contrast, constructs in which CaM was fused to truncated or mutant OspA N-terminal tether peptides were targeted to the periplasmic leaflet of the OM in the presence of calcium but could be flipped to the bacterial surface upon calcium chelation. This indicated that in the absence of an intact tether peptide, unfolding of the CaM moiety was required in order to facilitate OM traversal. Together, these data further support a periplasmic tether peptide-mediated mechanism to prevent premature folding of B. burgdorferi surface lipoproteins. The specific shift in the OM topology of sequence-identical lipopeptides due to a single-variable change in environmental conditions also indicates that surface-bound Borrelia lipoproteins can localize transiently to the periplasmic leaflet of the OM.
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99
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Determination of Borrelia surface lipoprotein anchor topology by surface proteolysis. J Bacteriol 2011; 193:6379-83. [PMID: 21908659 DOI: 10.1128/jb.05849-11] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We used a surface trypsinolysis assay to probe accessibility of the membrane-proximal N-terminal tether peptides of Borrelia surface lipoproteins OspA and Vsp1. Our findings with both wild-type and mutant proteins are only compatible with the anchoring of these surface lipoproteins in the outer leaflet of the outer spirochetal membrane.
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100
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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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