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Hodges FJ, Torres VVL, Cunningham AF, Henderson IR, Icke C. Redefining the bacterial Type I protein secretion system. Adv Microb Physiol 2023; 82:155-204. [PMID: 36948654 DOI: 10.1016/bs.ampbs.2022.10.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Type I secretion systems (T1SS) are versatile molecular machines for protein transport across the Gram-negative cell envelope. The archetypal Type I system mediates secretion of the Escherichia coli hemolysin, HlyA. This system has remained the pre-eminent model of T1SS research since its discovery. The classic description of a T1SS is composed of three proteins: an inner membrane ABC transporter, a periplasmic adaptor protein and an outer membrane factor. According to this model, these components assemble to form a continuous channel across the cell envelope, an unfolded substrate molecule is then transported in a one-step mechanism, directly from the cytosol to the extracellular milieu. However, this model does not encapsulate the diversity of T1SS that have been characterized to date. In this review, we provide an updated definition of a T1SS, and propose the subdivision of this system into five subgroups. These subgroups are categorized as T1SSa for RTX proteins, T1SSb for non-RTX Ca2+-binding proteins, T1SSc for non-RTX proteins, T1SSd for class II microcins, and T1SSe for lipoprotein secretion. Although often overlooked in the literature, these alternative mechanisms of Type I protein secretion offer many avenues for biotechnological discovery and application.
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Affiliation(s)
- Freya J Hodges
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia
| | - Von Vergel L Torres
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia
| | - Adam F Cunningham
- Institute of Immunology and Immunotherapy, University of Birmingham, Birmingham, United Kingdom
| | - Ian R Henderson
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia.
| | - Christopher Icke
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia.
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Elfageih R, Karyolaimos A, Kemp G, de Gier J, von Heijne G, Kudva R. Cotranslational folding of alkaline phosphatase in the periplasm of Escherichia coli. Protein Sci 2020; 29:2028-2037. [PMID: 32790204 PMCID: PMC7513700 DOI: 10.1002/pro.3927] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Revised: 08/08/2020] [Accepted: 08/11/2020] [Indexed: 01/10/2023]
Abstract
Cotranslational protein folding studies using Force Profile Analysis, a method where the SecM translational arrest peptide is used to detect folding-induced forces acting on the nascent polypeptide, have so far been limited mainly to small domains of cytosolic proteins that fold in close proximity to the translating ribosome. In this study, we investigate the cotranslational folding of the periplasmic, disulfide bond-containing Escherichia coli protein alkaline phosphatase (PhoA) in a wild-type strain background and a strain background devoid of the periplasmic thiol: disulfide interchange protein DsbA. We find that folding-induced forces can be transmitted via the nascent chain from the periplasm to the polypeptide transferase center in the ribosome, a distance of ~160 Å, and that PhoA appears to fold cotranslationally via at least two disulfide-stabilized folding intermediates. Thus, Force Profile Analysis can be used to study cotranslational folding of proteins in an extra-cytosolic compartment, like the periplasm.
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Affiliation(s)
- Rageia Elfageih
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
| | | | - Grant Kemp
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
| | - Jan‐Willem de Gier
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
| | - Gunnar von Heijne
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
- Science for Life Laboratory Stockholm UniversitySolnaSweden
| | - Renuka Kudva
- Department of Biochemistry and BiophysicsStockholm UniversityStockholmSweden
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Crane JM, Randall LL. The Sec System: Protein Export in Escherichia coli. EcoSal Plus 2017; 7:10.1128/ecosalplus.ESP-0002-2017. [PMID: 29165233 PMCID: PMC5807066 DOI: 10.1128/ecosalplus.esp-0002-2017] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Indexed: 11/20/2022]
Abstract
In Escherichia coli, proteins found in the periplasm or the outer membrane are exported from the cytoplasm by the general secretory, Sec, system before they acquire stably folded structure. This dynamic process involves intricate interactions among cytoplasmic and membrane proteins, both peripheral and integral, as well as lipids. In vivo, both ATP hydrolysis and proton motive force are required. Here, we review the Sec system from the inception of the field through early 2016, including biochemical, genetic, and structural data.
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Affiliation(s)
- Jennine M. Crane
- Department of Biochemistry, University of Missouri, Columbia, Missouri
| | - Linda L. Randall
- Department of Biochemistry, University of Missouri, Columbia, Missouri
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Secretion Chaperones PrsA2 and HtrA Are Required for Listeria monocytogenes Replication following Intracellular Induction of Virulence Factor Secretion. Infect Immun 2016; 84:3034-46. [PMID: 27481256 DOI: 10.1128/iai.00312-16] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Accepted: 07/27/2016] [Indexed: 12/25/2022] Open
Abstract
The Gram-positive bacterium Listeria monocytogenes transitions from an environmental organism to an intracellular pathogen following its ingestion by susceptible mammalian hosts. Bacterial replication within the cytosol of infected cells requires activation of the central virulence regulator PrfA followed by a PrfA-dependent induction of secreted virulence factors. The PrfA-induced secreted chaperone PrsA2 and the chaperone/protease HtrA contribute to the folding and stability of select proteins translocated across the bacterial membrane. L. monocytogenes strains that lack both prsA2 and htrA exhibit near-normal patterns of growth in broth culture but are severely attenuated in vivo We hypothesized that, in the absence of PrsA2 and HtrA, the increase in PrfA-dependent protein secretion that occurs following bacterial entry into the cytosol results in misfolded proteins accumulating at the bacterial membrane with a subsequent reduction in intracellular bacterial viability. Consistent with this hypothesis, the introduction of a constitutively activated allele of prfA (prfA*) into ΔprsA2 ΔhtrA strains was found to essentially inhibit bacterial growth at 37°C in broth culture. ΔprsA2 ΔhtrA strains were additionally found to be defective for cell invasion and vacuole escape in selected cell types, steps that precede full PrfA activation. These data establish the essential requirement for PrsA2 and HtrA in maintaining bacterial growth under conditions of PrfA activation. In addition, chaperone function is required for efficient bacterial invasion and rapid vacuole lysis within select host cell types, indicating roles for PrsA2/HtrA prior to cytosolic PrfA activation and the subsequent induction of virulence factor secretion.
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Structural basis for the antifolding activity of a molecular chaperone. Nature 2016; 537:202-206. [PMID: 27501151 PMCID: PMC5161705 DOI: 10.1038/nature18965] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 06/24/2016] [Indexed: 01/23/2023]
Abstract
Molecular chaperones act on non-native proteins in the cell to prevent their aggregation, premature folding or misfolding. Different chaperones often exert distinct effects, such as acceleration or delay of folding, on client proteins via mechanisms that are poorly understood. Here we report the solution structure of SecB, a chaperone that exhibits strong antifolding activity, in complex with alkaline phosphatase and maltose-binding protein captured in their unfolded states. SecB uses long hydrophobic grooves that run around its disk-like shape to recognize and bind to multiple hydrophobic segments across the length of non-native proteins. The multivalent binding mode results in proteins wrapping around SecB. This unique complex architecture alters the kinetics of protein binding to SecB and confers strong antifolding activity on the chaperone. The data show how the different architectures of chaperones result in distinct binding modes with non-native proteins that ultimately define the activity of the chaperone.
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Yan S, Wu G. Large-scale evolutionary analyses on SecB subunits of bacterial sec system. PLoS One 2015; 10:e0120417. [PMID: 25775430 PMCID: PMC4361572 DOI: 10.1371/journal.pone.0120417] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2014] [Accepted: 01/21/2015] [Indexed: 01/10/2023] Open
Abstract
Protein secretion systems are extremely important in bacteria because they are involved in many fundamental cellular processes. Of the various secretion systems, the Sec system is composed of seven different subunits in bacteria, and subunit SecB brings secreted preproteins to subunit SecA, which with SecYEG and SecDF forms a complex for the translocation of secreted preproteins through the inner membrane. Because of the wide existence of Sec system across bacteria, eukaryota, and archaea, each subunit of the Sec system has a complicated evolutionary relationship. Until very recently, 5,162 SecB sequences have been documented in UniProtKB, however no phylogenetic study has been conducted on a large sampling of SecBs from bacterial Sec secretion system, and no statistical study has been conducted on such size of SecBs in order to exhaustively investigate their variances of pairwise p-distance along taxonomic lineage from kingdom to phylum, to class, to order, to family, to genus and to organism. To fill in these knowledge gaps, 3,813 bacterial SecB sequences with full taxonomic lineage from kingdom to organism covering 4 phyla, 11 classes, 41 orders, 82 families, 269 genera, and 3,744 organisms were studied. Phylogenetic analysis revealed how the SecBs evolved without compromising their function with examples of 3-D structure comparison of two SecBs from Proteobacteria, and possible factors that affected the SecB evolution were considered. The average pairwise p-distances showed that the variance varied greatly in each taxonomic group. Finally, the variance was further partitioned into inter- and intra-clan variances, which could correspond to vertical and horizontal gene transfers, with relevance for Achromobacter, Brevundimonas, Ochrobactrum, and Pseudoxanthomonas.
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Affiliation(s)
- Shaomin Yan
- State Key Laboratory of Non-food Biomass Enzyme Technology, National Engineering Research Center for Non-food Biorefinery, Guangxi Biomass Industrialization Engineering Institute, Guangxi Key Laboratory of Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning, Guangxi, 530007, China
| | - Guang Wu
- State Key Laboratory of Non-food Biomass Enzyme Technology, National Engineering Research Center for Non-food Biorefinery, Guangxi Biomass Industrialization Engineering Institute, Guangxi Key Laboratory of Biorefinery, Guangxi Academy of Sciences, 98 Daling Road, Nanning, Guangxi, 530007, China
- * E-mail:
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Sala A, Bordes P, Genevaux P. Multitasking SecB chaperones in bacteria. Front Microbiol 2014; 5:666. [PMID: 25538690 PMCID: PMC4257090 DOI: 10.3389/fmicb.2014.00666] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 11/17/2014] [Indexed: 12/17/2022] Open
Abstract
Protein export in bacteria is facilitated by the canonical SecB chaperone, which binds to unfolded precursor proteins, maintains them in a translocation competent state and specifically cooperates with the translocase motor SecA to ensure their proper targeting to the Sec translocon at the cytoplasmic membrane. Besides its key contribution to the Sec pathway, SecB chaperone tasking is critical for the secretion of the Sec-independent heme-binding protein HasA and actively contributes to the cellular network of chaperones that control general proteostasis in Escherichia coli, as judged by the significant interplay found between SecB and the trigger factor, DnaK and GroEL chaperones. Although SecB is mainly a proteobacterial chaperone associated with the presence of an outer membrane and outer membrane proteins, secB-like genes are also found in Gram-positive bacteria as well as in certain phages and plasmids, thus suggesting alternative functions. In addition, a SecB-like protein is also present in the major human pathogen Mycobacterium tuberculosis where it specifically controls a stress-responsive toxin–antitoxin system. This review focuses on such very diverse chaperone functions of SecB, both in E. coli and in other unrelated bacteria.
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Affiliation(s)
- Ambre Sala
- Laboratoire de Microbiologie et Génétique Moléculaire, Centre National de la Recherche Scientifique, Université Paul Sabatier, Toulouse, France
| | - Patricia Bordes
- Laboratoire de Microbiologie et Génétique Moléculaire, Centre National de la Recherche Scientifique, Université Paul Sabatier, Toulouse, France
| | - Pierre Genevaux
- Laboratoire de Microbiologie et Génétique Moléculaire, Centre National de la Recherche Scientifique, Université Paul Sabatier, Toulouse, France
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López-Leal G, Tabche ML, Castillo-Ramírez S, Mendoza-Vargas A, Ramírez-Romero MA, Dávila G. RNA-Seq analysis of the multipartite genome of Rhizobium etli CE3 shows different replicon contributions under heat and saline shock. BMC Genomics 2014; 15:770. [PMID: 25201548 PMCID: PMC4167512 DOI: 10.1186/1471-2164-15-770] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 09/03/2014] [Indexed: 12/23/2022] Open
Abstract
Background Regulation of transcription is essential for any organism and Rhizobium etli (a multi-replicon, nitrogen-fixing symbiotic bacterium) is no exception. This bacterium is commonly found in the rhizosphere (free-living) or inside of root-nodules of the common bean (Phaseolus vulgaris) in a symbiotic relationship. Abiotic stresses, such as high soil temperatures and salinity, compromise the genetic stability of R. etli and therefore its symbiotic interaction with P. vulgaris. However, it is still unclear which genes are up- or down-regulated to cope with these stress conditions. The aim of this study was to identify the genes and non-coding RNAs (ncRNAs) that are differentially expressed under heat and saline shock, as well as the promoter regions of the up-regulated loci. Results Analysing the heat and saline shock responses of R. etli CE3 through RNA-Seq, we identified 756 and 392 differentially expressed genes, respectively, and 106 were up-regulated under both conditions. Notably, the set of genes over-expressed under either condition was preferentially encoded on plasmids, although this observation was more significant for the heat shock response. In contrast, during either saline shock or heat shock, the down-regulated genes were principally chromosomally encoded. Our functional analysis shows that genes encoding chaperone proteins were up-regulated during the heat shock response, whereas genes involved in the metabolism of compatible solutes were up-regulated following saline shock. Furthermore, we identified thirteen and nine ncRNAs that were differentially expressed under heat and saline shock, respectively, as well as eleven ncRNAs that had not been previously identified. Finally, using an in silico analysis, we studied the promoter motifs in all of the non-coding regions associated with the genes and ncRNAs up-regulated under both conditions. Conclusions Our data suggest that the replicon contribution is different for different stress responses and that the heat shock response is more complex than the saline shock response. In general, this work exemplifies how strategies that not only consider differentially regulated genes but also regulatory elements of the stress response provide a more comprehensive view of bacterial gene regulation. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-770) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Gamaliel López-Leal
- Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, Cuernavaca, Morelos C,P 62210, México.
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Abdian PL, Caramelo JJ, Ausmees N, Zorreguieta A. RapA2 is a calcium-binding lectin composed of two highly conserved cadherin-like domains that specifically recognize Rhizobium leguminosarum acidic exopolysaccharides. J Biol Chem 2012; 288:2893-904. [PMID: 23235153 DOI: 10.1074/jbc.m112.411769] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
In silico analyses have revealed a conserved protein domain (CHDL) widely present in bacteria that has significant structural similarity to eukaryotic cadherins. A CHDL domain was shown to be present in RapA, a protein that is involved in autoaggregation of Rhizobium cells, biofilm formation, and adhesion to plant roots as shown by us and others. Structural similarity to cadherins suggested calcium-dependent oligomerization of CHDL domains as a mechanistic basis for RapA action. Here we show by circular dichroism spectroscopy, light scattering, isothermal titration calorimetry, and other methods that RapA2 from Rhizobium leguminosarum indeed exhibits a cadherin-like β-sheet conformation and that its proper folding and stability are dependent on the binding of one calcium ion per protein molecule. By further in silico analysis we also reveal that RapA2 consists of two CHDL domains and expand the range of CHDL-containing proteins in bacteria and archaea. However, light scattering assays at various concentrations of added calcium revealed that RapA2 formed neither homo-oligomers nor hetero-oligomers with RapB (a distinct CHDL protein), indicating that RapA2 does not mediate cellular interactions through a cadherin-like mechanism. Instead, we demonstrate that RapA2 interacts specifically with the acidic exopolysaccharides (EPSs) produced by R. leguminosarum in a calcium-dependent manner, sustaining a role of these proteins in the development of the biofilm matrix made of EPS. Because EPS binding by RapA2 can only be attributed to its two CHDL domains, we propose that RapA2 is a calcium-dependent lectin and that CHDL domains in various bacterial and archaeal proteins confer carbohydrate binding activity to these proteins.
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Affiliation(s)
- Patricia L Abdian
- Fundación Instituto Leloir, IIBBA Consejo Nacional de Investigaciones Científicas y Tecnológicas, Patricias Argentinas 435, C1405BWE Buenos Aires, Argentina
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Dalbey RE, Kuhn A. Protein Traffic in Gram-negative bacteria – how exported and secreted proteins find their way. FEMS Microbiol Rev 2012; 36:1023-45. [DOI: 10.1111/j.1574-6976.2012.00327.x] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2011] [Accepted: 01/04/2012] [Indexed: 11/27/2022] Open
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Linhartová I, Bumba L, Mašín J, Basler M, Osička R, Kamanová J, Procházková K, Adkins I, Hejnová-Holubová J, Sadílková L, Morová J, Sebo P. RTX proteins: a highly diverse family secreted by a common mechanism. FEMS Microbiol Rev 2011; 34:1076-112. [PMID: 20528947 PMCID: PMC3034196 DOI: 10.1111/j.1574-6976.2010.00231.x] [Citation(s) in RCA: 360] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Repeats-in-toxin (RTX) exoproteins of Gram-negative bacteria form a steadily growing family of proteins with diverse biological functions. Their common feature is the unique mode of export across the bacterial envelope via the type I secretion system and the characteristic, typically nonapeptide, glycine- and aspartate-rich repeats binding Ca2+ ions. In this review, we summarize the current state of knowledge on the organization of rtx loci and on the biological and biochemical activities of therein encoded proteins. Applying several types of bioinformatic screens on the steadily growing set of sequenced bacterial genomes, over 1000 RTX family members were detected, with the biological functions of most of them remaining to be characterized. Activities of the so far characterized RTX family members are then discussed and classified according to functional categories, ranging from the historically first characterized pore-forming RTX leukotoxins, through the large multifunctional enzymatic toxins, bacteriocins, nodulation proteins, surface layer proteins, up to secreted hydrolytic enzymes exhibiting metalloprotease or lipase activities of industrial interest.
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Affiliation(s)
- Irena Linhartová
- Institute of Microbiology AS CR v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic
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Appraisal of translocation pathways for displaying ankyrin repeat protein on phage particles. Protein Expr Purif 2010; 74:156-61. [DOI: 10.1016/j.pep.2010.08.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2010] [Revised: 08/20/2010] [Accepted: 08/20/2010] [Indexed: 01/01/2023]
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Bakkes PJ, Jenewein S, Smits SHJ, Holland IB, Schmitt L. The rate of folding dictates substrate secretion by the Escherichia coli hemolysin type 1 secretion system. J Biol Chem 2010; 285:40573-80. [PMID: 20971850 DOI: 10.1074/jbc.m110.173658] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Secretion of the Escherichia coli toxin hemolysin A (HlyA) is catalyzed by the membrane protein complex HlyB-HlyD-TolC and requires a secretion sequence located within the last 60 amino acids of HlyA. The Hly translocator complex exports a variety of passenger proteins when fused N-terminal to this secretion sequence. However, not all fusions are secreted efficiently. Here, we demonstrate that the maltose binding protein (MalE) lacking its natural export signal and fused to the HlyA secretion signal is poorly secreted by the Hly system. We anticipated that folding kinetics might be limiting secretion, and we therefore introduced the "folding" mutation Y283D. Indeed this mutant fusion protein was secreted at a much higher level. This level was further enhanced by the introduction of a second MalE folding mutation (V8G or A276G). Secretion did not require the molecular chaperone SecB. Folding analysis revealed that all mutations reduced the refolding rate of the substrate, whereas the unfolding rate was unaffected. Thus, the efficiency of secretion by the Hly system is dictated by the folding rate of the substrate. Moreover, we demonstrate that fusion proteins defective in export can be engineered for secretion while still retaining function.
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Affiliation(s)
- Patrick J Bakkes
- Institute of Biochemistry, Heinrich Heine University Duesseldorf, Universitaetsstrasse 1, 40225 Duesseldorf, Germany
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Multiple signals direct the assembly and function of a type 1 secretion system. J Bacteriol 2010; 192:3861-9. [PMID: 20418390 DOI: 10.1128/jb.00178-10] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Type 1 secretion systems (T1SS) are present in a wide range of Gram-negative bacteria and are involved in the secretion of diverse substrates such as proteases, lipases, and hemophores. T1SS consist of three proteins: an inner membrane ABC (ATP binding cassette) protein, a periplasmic adaptor, and an outer membrane channel of the TolC family. Assembly of the tripartite complex is transient and induced upon binding of the substrate to the ABC protein. It is generally accepted that T1SS-secreted proteins have a C-terminal secretion signal required for secretion and that this signal interacts with the ABC protein. However, we have previously shown that for the Serratia marcescens hemophore HasA, interactions with the ABC protein and subsequent T1SS assembly require additional regions. In this work, we characterize these regions and demonstrate that they are numerous, distributed throughout the HasA polypeptide, and most likely linear. Together with the C-terminal signal, these elements maximize the secretion of HasA. The data also show that the C-terminal signal of HasA triggers HasD-driven ATP hydrolysis, leading to disassembly of the complex. These data support a model of type 1 secretion involving a multistep interaction between the substrate and the ABC protein that stabilizes the assembled secretion system until the C terminus is presented. This model also supports tight coupling between synthesis and secretion.
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Bechtluft P, Nouwen N, Tans SJ, Driessen AJM. SecB--a chaperone dedicated to protein translocation. MOLECULAR BIOSYSTEMS 2009; 6:620-7. [PMID: 20237639 DOI: 10.1039/b915435c] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
SecB is a molecular chaperone in Gram-negative bacteria dedicated to the post-translational translocation of proteins across the cytoplasmic membrane. The entire surface of this chaperone is used for both of its native functions in protein targeting and unfolding. Single molecule studies revealed how SecB affects the folding pathway of proteins and how it prevents the tertiary structure formation and aggregation to support protein translocation.
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Affiliation(s)
- Philipp Bechtluft
- Department of Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute and the Zernike Institute for Advanced Materials, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.
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Chenal A, Guijarro JI, Raynal B, Delepierre M, Ladant D. RTX calcium binding motifs are intrinsically disordered in the absence of calcium: implication for protein secretion. J Biol Chem 2008; 284:1781-9. [PMID: 19015266 DOI: 10.1074/jbc.m807312200] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The Repeat in Toxin (RTX) motif is a tandemly repeated calcium-binding nonapeptide sequence present in proteins that are secreted by the type I secretion system (T1SS) of Gram-negative bacteria. Here, we have characterized the structural and hydrodynamic properties of the RTX Repeat Domain (RD) of the CyaA toxin from Bordetella pertussis. This 701-amino acid long domain contains about 40 RTX motifs. We showed that, in the absence of calcium, RD was natively disordered, weakly stable, and highly hydrated. Calcium binding induced compaction and dehydration of RD, along with the formation of stable secondary and tertiary structures. The calcium-induced conformational switch between unfolded conformations of apo-RD and stable structures of holo-RD is likely to be a key property for the biological function of the CyaA toxin: in the low calcium environment of the bacterial cytosol, the intrinsically disordered character of the protein may facilitate its secretion through the secretion machinery. In the extracellular medium, calcium binding can then trigger the folding of the polypeptide into its functional state. The intrinsic disorder of RTX-containing proteins in the absence of calcium may thus be directly involved in the efficient secretion of proteins through T1SS.
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Affiliation(s)
- Alexandre Chenal
- Institut Pasteur, Unité de Biochimie des Interactions Macromoléculaires, Paris, France.
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Structure, function, and evolution of bacterial ATP-binding cassette systems. Microbiol Mol Biol Rev 2008; 72:317-64, table of contents. [PMID: 18535149 DOI: 10.1128/mmbr.00031-07] [Citation(s) in RCA: 938] [Impact Index Per Article: 58.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
SUMMARY ATP-binding cassette (ABC) systems are universally distributed among living organisms and function in many different aspects of bacterial physiology. ABC transporters are best known for their role in the import of essential nutrients and the export of toxic molecules, but they can also mediate the transport of many other physiological substrates. In a classical transport reaction, two highly conserved ATP-binding domains or subunits couple the binding/hydrolysis of ATP to the translocation of particular substrates across the membrane, through interactions with membrane-spanning domains of the transporter. Variations on this basic theme involve soluble ABC ATP-binding proteins that couple ATP hydrolysis to nontransport processes, such as DNA repair and gene expression regulation. Insights into the structure, function, and mechanism of action of bacterial ABC proteins are reported, based on phylogenetic comparisons as well as classic biochemical and genetic approaches. The availability of an increasing number of high-resolution structures has provided a valuable framework for interpretation of recent studies, and realistic models have been proposed to explain how these fascinating molecular machines use complex dynamic processes to fulfill their numerous biological functions. These advances are also important for elucidating the mechanism of action of eukaryotic ABC proteins, because functional defects in many of them are responsible for severe human inherited diseases.
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Cescau S, Cwerman H, Létoffé S, Delepelaire P, Wandersman C, Biville F. Heme acquisition by hemophores. Biometals 2007; 20:603-13. [PMID: 17268821 DOI: 10.1007/s10534-006-9050-y] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2006] [Accepted: 11/28/2006] [Indexed: 01/02/2023]
Abstract
Bacterial hemophores are secreted to the extracellular medium, where they scavenge heme from various hemoproteins due to their higher affinity for this compound, and return it to their specific outer membrane receptor. HasR, the outer membrane receptor of the HasA hemophore, assumes multiple functions which require various energy levels. Binding of heme and, of heme-free or heme-loaded hemophores is energy-independent. Heme transfer from the holo-hemophore to the outer membrane receptor is also energy-independent. In contrast, heme transport and hemophore release require basal or high levels of TonB and proton motive force, respectively. In addition, HasR is a component of a signaling cascade, regulating expression of the has operon via specific sigma and anti-sigma factors encoded by genes clustered at the has operon. The signal is the heme landing on HasR in the presence of the hemophore in its apo form. The has system is the only system thus far characterized in which the anti-sigma factor is submitted to the same signaling cascade as the target operon. Specific autoregulation of the has system, combined with negative regulation by the Fur protein, permits bacterial adaptation to the available iron source. In the presence of a heme-loaded hemophore, inactive anti-sigma factor is accumulated and can be activated as soon as the heme source dries up. Hence, the has system, instead of being submitted to amplification like other systems regulated by sigma anti-sigma factors, functions by pulses triggered by heme availability.
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Affiliation(s)
- S Cescau
- Unité des Membranes Bactériennes, Département de Microiologie, URA CNRS 2172 Institut Pasteur, 25, rue du Dr. Roux, 75024 Paris Cedex 15, France
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Czjzek M, Létoffé S, Wandersman C, Delepierre M, Lecroisey A, Izadi-Pruneyre N. The crystal structure of the secreted dimeric form of the hemophore HasA reveals a domain swapping with an exchanged heme ligand. J Mol Biol 2006; 365:1176-86. [PMID: 17113104 DOI: 10.1016/j.jmb.2006.10.063] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2006] [Revised: 10/16/2006] [Indexed: 10/24/2022]
Abstract
To satisfy their iron needs, several Gram-negative bacteria use a heme uptake system involving an extracellular heme-binding protein called hemophore. The function of the hemophore is to acquire free or hemoprotein-bound heme and to transfer it to HasR, its specific outer membrane receptor, by protein-protein interaction. The hemophore HasA secreted by Serratia marcescens, an opportunistic pathogen, was the first to be identified and is now very well characterized. HasA is a monomer that binds one b heme with strong affinity. The heme in HasA is highly exposed to solvent and coordinated by an unusual pair of ligands, a histidine and a tyrosine. Here, we report the identification, the characterization and the X-ray structure of a dimeric form of HasA from S. marcescens: DHasA. We show that both monomeric and dimeric forms are secreted in iron deficient conditions by S. marcescens. The crystal structure of DHasA reveals that it is a domain swapped dimer. The overall structure of each monomeric subunit of DHasA is very similar to that of HasA but formed by parts coming from the two different polypeptide chains, involving one of the heme ligands. Consequently DHasA binds two heme molecules by residues coming from both polypeptide chains. We show here that, while DHasA can bind two heme molecules, it is not able to deliver them to the receptor HasR. However, DHasA can efficiently transfer its heme to the monomeric form that, in turn, delivers it to HasR. We assume that DHasA can function as a heme reservoir in the hemophore system.
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Affiliation(s)
- Mirjam Czjzek
- CNRS, Université Pierre et Marie Curie-Paris 6, Laboratoire International Associé-Dispersal and Adaptation in Marine Species, Unité Mixte de Recherche 7139, Station Biologique, F-29682 Roscoff Cedex, France
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Pimenta AL, Racher K, Jamieson L, Blight MA, Holland IB. Mutations in HlyD, part of the type 1 translocator for hemolysin secretion, affect the folding of the secreted toxin. J Bacteriol 2005; 187:7471-80. [PMID: 16237030 PMCID: PMC1272971 DOI: 10.1128/jb.187.21.7471-7480.2005] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
HlyD, a member of the membrane fusion protein family, is essential for the secretion of the RTX hemolytic toxin HlyA from Escherichia coli. Random point mutations affecting HlyA secretion were obtained, distributed in most periplasmic regions of the HlyD molecule. Analysis of the secretion phenotypes of different mutants allowed the identification of regions in HlyD involved in different steps of HlyA translocation. Four mutants, V349-I, T85-I, V334-I and L165-Q, were conditionally defective, a phenotype shown to be linked to the presence of inhibitory concentrations of Ca2+ in extracellular medium. Hly mutant T85-I was defective at an early stage in secretion, while mutants V334-I and L165-Q appeared to accumulate HlyA in the cell envelope, indicating a block at an intermediate step. Mutants V349-I, V334-I, and L165-Q were only partially defective in secretion, allowing significant levels of HlyA to be transported, but in the case of V349-I and L165-Q the HlyA molecules secreted showed greatly reduced hemolytic activity. Hemolysin molecules secreted from V349-I and V334-I are defective in normal folding and can be reactivated in vitro to the same levels as HlyA secreted from the wild-type translocator. Both V349-I and V334-I mutations mapped to the C-terminal lipoyl repeat motif, involved in the switching from the helical hairpin to the extended form of HlyD during assembly of the functional transport channel. These results suggest that HlyD is an integral component of the transport pathway, whose integrity is essential for the final folding of secreted HlyA into its active form.
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Affiliation(s)
- A L Pimenta
- Université de Cergy Pontoise, Department of Biology, ERRMECe, 2 Av. Adolphe Chauvin, 95302Cergy-Pontoise cedex, France.
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Holland IB, Schmitt L, Young J. Type 1 protein secretion in bacteria, the ABC-transporter dependent pathway (review). Mol Membr Biol 2005; 22:29-39. [PMID: 16092522 DOI: 10.1080/09687860500042013] [Citation(s) in RCA: 164] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The relatively simple type 1 secretion system in gram-negative bacteria is nevertheless capable of transporting polypeptides of up to 800 kDa across the cell envelope in a few seconds. The translocator is composed of an ABC-transporter, providing energy through ATP hydrolysis (and perhaps the initial channel across the inner membrane), linked to a multimeric Membrane Fusion Protein (MFP) spanning the initial part of the periplasm and forming a continuous channel to the surface with an outer membrane trimeric protein. Proteins targeted to the translocator carry an (uncleaved), poorly conserved secretion signal of approximately 50 residues. In E. coli the HlyA toxin interacts with both the MFP (HlyD) and the ABC protein HlyB, (a half transporter) triggering, via a conformational change in HlyD, recruitment of the third component, TolC, into the transenvelope complex. In vitro, HlyA, through its secretion signal, binds to the nucleotide binding domain (NBD or ABC-ATPase) of HlyB in a reaction reversible by ATP that may mimic initial movement of HlyA into the translocation channel. HlyA is then transported rapidly, apparently in an unfolded form, to the cell surface, where folding and release takes place. Whilst recent structural studies of TolC and MFP-like proteins are providing atomic detail of much of the transport path, structural analysis of the HlyB NBD and other ABC ATPases, have revealed details of the catalytic cycle within an NBD dimer and a glimpse of how the action of HlyB is coupled to the translocation of HlyA.
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Affiliation(s)
- I Barry Holland
- Institut de Génétique et Microbiologie, CNRS UMR 8621, Université Paris-Sud, Orsay Cedex, France.
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Zhou J, Xu Z. The structural view of bacterial translocation-specific chaperone SecB: implications for function. Mol Microbiol 2005; 58:349-57. [PMID: 16194224 DOI: 10.1111/j.1365-2958.2005.04842.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
SecB is a molecular chaperone that functions in bacterial post-translational protein translocation pathway. It maintains newly synthesized precursor polypeptide chains in a translocation-competent state and guides them to the translocon via its high-affinity binding to the ligand as well as to the membrane-embedded ATPase SecA. Recent advances in elucidating the structures of SecB have enabled the examination of protein function in the structural context. Structures of SecB from both Haemophilus influenzae and Escherichia coli support the early two-subsite polypeptide-binding model. In addition, the detailed molecular interaction between SecB and SecA was revealed by a structure of SecB in complex with the C-terminal zinc-containing domain of SecA. These observations explain the dual role of SecB plays in the translocation pathway, as a molecular chaperone and a specific targeting factor. A model of SecB-SecA complex suggests that the binding of SecA to SecB changes the conformation of the polypeptide binding sites in the chaperone, enabling transfer of precursor polypeptides from SecB to SecA. Recent studies also show the presence of a second zinc-independent SecB binding site in SecA and the new interaction might contribute to the function of SecB.
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Affiliation(s)
- Jiahai Zhou
- Department of Biological Chemistry, Medical School and Life Sciences Institute, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, MI 48109-2216, USA
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Delepelaire P. Type I secretion in gram-negative bacteria. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2004; 1694:149-61. [DOI: 10.1016/j.bbamcr.2004.05.001] [Citation(s) in RCA: 308] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2004] [Revised: 05/03/2004] [Accepted: 05/05/2004] [Indexed: 12/22/2022]
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Fraile S, Muñoz A, de Lorenzo V, Fernández LA. Secretion of proteins with dimerization capacity by the haemolysin type I transport system of Escherichia coli. Mol Microbiol 2004; 53:1109-21. [PMID: 15306015 DOI: 10.1111/j.1365-2958.2004.04205.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The tolerance of the haemolysin transport system (Hly) for exporting dimeric protein substrates to the supernatants of Escherichia coli cultures was examined. A strong dimerization domain (i.e. an amphipathic alpha-helix capable of forming a leucine zipper in the yeast transcription factor GCN4) was inserted into an epitope-tagged version of the 23 kDa C-terminal secretion signal of haemolysin (EHlyA). The zipper-containing polypeptide (ZEHlyA) was effectively secreted by E. coli cells carrying the HlyBD transporter and accumulated in the culture media as a stable dimer as determined by gel filtration chromatography. In vivo protein cross-linking experiments and coexpression with a secretion-deficient derivative of ZEHlyA indicated that leucine zipper-dependent dimerization occurs following secretion. To test whether dimerization allows the correct folding of the secreted polypeptide, immunoglobulin V(HH)-domains obtained from camel antibodies were fused to EHlyA and ZEHlyA. Functional dimerization of the ZEHlyA hybrid was anticipated to increase the apparent binding affinity (i.e. avidity) of the V(HH) moiety, thus becoming an excellent reporter of correct protein folding and dimerization. Both V(HH)-EHlyA and V(HH)-ZEHlyA hybrids were quantitatively secreted and found in the extracellular medium as active monomers and dimers respectively. When compared with their monomeric counterparts, the dimeric V(HH)-ZEHlyA molecules showed superior binding properties to their cognate antigen, with a 10-fold increase in their avidity. These data reveal a non-anticipated permissiveness of the Hly type I transport machinery for the secretion of substrates with dimerization capacity.
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Affiliation(s)
- Sofía Fraile
- Centro Nacional de Biotecnología del Consejo Superior de Investigaciones Científicas (CSIC), Campus de Cantoblanco, 28049 Madrid, Spain
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