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Bunduc CM, Ding Y, Kuijl C, Marlovits TC, Bitter W, Houben ENG. Reconstitution of a minimal ESX-5 type VII secretion system suggests a role for PPE proteins in the outer membrane transport of proteins. mSphere 2023; 8:e0040223. [PMID: 37747201 PMCID: PMC10597459 DOI: 10.1128/msphere.00402-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Accepted: 08/03/2023] [Indexed: 09/26/2023] Open
Abstract
Mycobacteria utilize type VII secretion systems (T7SSs) to secrete proteins across their highly hydrophobic and diderm cell envelope. Pathogenic mycobacteria have up to five different T7SSs, called ESX-1 to ESX-5, which are crucial for growth and virulence. Here, we use a functionally reconstituted ESX-5 system in the avirulent species Mycobacterium smegmatis that lacks ESX-5, to define the role of each esx-5 gene in system functionality. By creating an array of gene deletions and assessing protein levels of components and membrane complex assembly, we observed that only the five components of the inner membrane complex are required for its assembly. However, in addition to these five core components, active secretion also depends on both the Esx and PE/PPE substrates. Tagging the PPE substrates followed by subcellular fractionation, surface labeling and membrane extraction showed that these proteins localize to the mycobacterial outer membrane. This indicates that they could play a role in secretion across this enigmatic outer barrier. These results provide the first full overview of the role of each esx-5 gene in T7SS functionality. IMPORTANCE Pathogenic mycobacteria, such as the notorious Mycobacterium tuberculosis, are highly successful as pathogens, in part due to their specific and diderm cell envelope, with a mycolic acid-containing outer membrane. The architecture of this highly impermeable membrane is little understood and the proteins that populate it even less so. To transport proteins across their cell envelope, mycobacteria employ a specialized transport pathway called type VII secretion. While recent studies have elucidated the type VII secretion membrane channel that mediates transport across the inner membrane, the identity of the outer membrane channel remains a black box. Here, we show evidence that specific substrates of the type VII pathway could form these channels. Elucidating the pathway and mechanism of protein secretion through the mycobacterial outer membrane will allow its exploitation for the development of novel mycobacterial therapeutics.
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Affiliation(s)
- C. M. Bunduc
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
- Centre for Structural Systems Biology, Notkestraße, Hamburg, Germany
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Notkestraße, Hamburg, Germany
- German Electron Synchrotron Centre, Notkestraße, Hamburg, Germany
| | - Y. Ding
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
| | - C. Kuijl
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Amsterdam, The Netherlands
| | - T. C. Marlovits
- Centre for Structural Systems Biology, Notkestraße, Hamburg, Germany
- Institute of Structural and Systems Biology, University Medical Center Hamburg-Eppendorf, Notkestraße, Hamburg, Germany
- German Electron Synchrotron Centre, Notkestraße, Hamburg, Germany
| | - W. Bitter
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Amsterdam, The Netherlands
| | - E. N. G. Houben
- Molecular Microbiology Section, Amsterdam Institute for Life and Environment (A-Life), Vrije Universiteit, Amsterdam, The Netherlands
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Izquierdo Lafuente B, Ummels R, Kuijl C, Bitter W, Speer A. Mycobacterium tuberculosis Toxin CpnT Is an ESX-5 Substrate and Requires Three Type VII Secretion Systems for Intracellular Secretion. mBio 2021; 12:e02983-20. [PMID: 33653883 PMCID: PMC8092274 DOI: 10.1128/mbio.02983-20] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 01/25/2021] [Indexed: 11/20/2022] Open
Abstract
CpnT, a NAD+ glycohydrolase, is the only known toxin that is secreted by Mycobacterium tuberculosis CpnT is composed of two domains; the C-terminal domain is the toxin, whereas the N-terminal domain is required for secretion. CpnT shows characteristics of type VII secretion (T7S) substrates, including a predicted helix-turn-helix domain followed by a secretion motif (YxxxE). Disruption of this motif indeed abolished CpnT secretion. By analyzing different mutants, we established that CpnT is specifically secreted by the ESX-5 system in Mycobacterium marinum under axenic conditions and during macrophage infection. Surprisingly, intracellular secretion of CpnT was also dependent on both ESX-1 and ESX-4. These secretion defects could be partially rescued by coinfection with wild-type bacteria, indicating that secreted effectors are involved in this process. In summary, our data reveal that three different type VII secretion systems have to be functional in order to observe intracellular secretion of the toxin CpnT.IMPORTANCE For decades, it was believed that the intracellular pathogen M. tuberculosis does not possess toxins. Only fairly recently it was discovered that CpnT is a potent secreted toxin of M. tuberculosis, causing necrotic cell death in host cells. However, until now the secretion pathway remained unknown. In our study, we were able to identify CpnT as a substrate of the mycobacterial type VII secretion system. Pathogenic mycobacteria have up to five different type VII secretion systems, called ESX-1 to ESX-5, which play distinct roles for the pathogen during growth or infection. We were able to elucidate that CpnT is exclusively secreted by the ESX-5 system in bacterial culture. However, to our surprise we discovered that, during infection studies, CpnT secretion relies on intact ESX-1, ESX-4, and ESX-5 systems. We elucidate for the first time the intertwined interplay of three different and independent secretion systems to secrete one substrate during infection.
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Affiliation(s)
- B Izquierdo Lafuente
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - R Ummels
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Location VU Medical Center, Amsterdam, The Netherlands
| | - C Kuijl
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Location VU Medical Center, Amsterdam, The Netherlands
| | - W Bitter
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Location VU Medical Center, Amsterdam, The Netherlands
| | - A Speer
- Department of Medical Microbiology and Infection Control, Amsterdam UMC, Location VU Medical Center, Amsterdam, The Netherlands
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Abstract
Bacteria have evolved intricate secretion machineries for the successful delivery of large molecules across their cell envelopes. Such specialized secretion systems allow a variety of bacteria to thrive in specific host environments. In mycobacteria, type VII secretion systems (T7SSs) are dedicated protein transport machineries that fulfill diverse and crucial roles, ranging from metabolite uptake to immune evasion and subversion to conjugation. Since the discovery of mycobacterial T7SSs about 15 y ago, genetic, structural, and functional studies have provided insight into the roles and functioning of these secretion machineries. Here, we focus on recent advances in the elucidation of the structure and mechanism of mycobacterial T7SSs in protein secretion. As many of these systems are essential for mycobacterial growth or virulence, they provide opportunities for the development of novel therapies to combat a number of relevant mycobacterial diseases.
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Affiliation(s)
- Catalin M. Bunduc
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HZ Amsterdam, The Netherlands
| | - W. Bitter
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HZ Amsterdam, The Netherlands
- Department of Medical Microbiology and Infection Control, Amsterdam Infection and Immunity Institute, Amsterdam University Medical Centers, 1007 MB Amsterdam, The Netherlands
| | - E.N.G. Houben
- Section of Molecular Microbiology, Amsterdam Institute of Molecular and Life Sciences, Vrije Universiteit Amsterdam, 1081 HZ Amsterdam, The Netherlands
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4
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Appelmelk BJ, den Dunnen J, Driessen NN, Ummels R, Pak M, Nigou J, Larrouy-Maumus G, Gurcha SS, Movahedzadeh F, Geurtsen J, Brown EJ, Eysink Smeets MM, Besra GS, Willemsen PTJ, Lowary TL, van Kooyk Y, Maaskant JJ, Stoker NG, van der Ley P, Puzo G, Vandenbroucke-Grauls CMJE, Wieland CW, van der Poll T, Geijtenbeek TBH, van der Sar AM, Bitter W. The mannose cap of mycobacterial lipoarabinomannan does not dominate the Mycobacterium–host interaction. Cell Microbiol 2008; 10:930-44. [DOI: 10.1111/j.1462-5822.2007.01097.x] [Citation(s) in RCA: 101] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Helwig U, Rubin D, Kiosz J, Bitter W, Schreiber S, Döring F, Fölsch UR, Schrezenmeir J. The effects of retinol on postprandial parameters in men with different FABP2 promoter haplotypes. Horm Metab Res 2007; 39:237-43. [PMID: 17447159 DOI: 10.1055/s-2007-972578] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The fatty acid binding protein 2 (FABP2) mediates the intestinal uptake of fatty acids. We and others have identified six FABP2 promoter polymorphisms which result in two haplotypes, A and B. Reporter-gene assays indicated different activity in FABP2 promoter alleles A and B and different responsiveness to PPAR ligands. IN SILICO analysis revealed different putative binding sites in FABP2 haplotypes for retinoid-dependent transcription factors. Therefore, we assumed that retinol supplementation may effect postprandial fat uptake differently in men with FABP2 promoter haplotype A and B. To test this hypothesis, we administered 5000 I.U. retinol/day for 8 weeks to 19 homozygotes for AA and 21 homozygotes for BB and assessed the alteration of postprandial triglycerides during this intervention. FABP2 genotype groups did not significantly differ in anthropometric and laboratory parameters. The alteration of postprandial triglycerides did not differ significantly between genotypes during intervention. This also held true after adjustment for BMI. Furthermore, in a subgroup which had a combination of promoter and common exon polymorphism, the alteration of the postprandial triglycerides did not differ between genotypes. In conclusion, the postprandial triglyceride metabolism of FABP2 promoter AA and BB did not respond differently to retinol administration even though IN SILICO analysis suggested this.
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Affiliation(s)
- U Helwig
- Federal Research Centre for Nutrition and Food, Location Kiel, Kiel, Germany.
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Folders J, Algra J, Roelofs MS, van Loon LC, Tommassen J, Bitter W. Characterization of Pseudomonas aeruginosa chitinase, a gradually secreted protein. J Bacteriol 2001; 183:7044-52. [PMID: 11717261 PMCID: PMC95551 DOI: 10.1128/jb.183.24.7044-7052.2001] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The gram-negative bacterium Pseudomonas aeruginosa secretes many proteins into its extracellular environment via the type I, II, and III secretion systems. In this study, a gene, chiC, coding for an extracellular chitinolytic enzyme, was identified. The chiC gene encodes a polypeptide of 483 amino acid residues, without a typical N-terminal signal sequence. Nevertheless, an N-terminal segment of 11 residues was found to be cleaved off in the secreted protein. The protein shows sequence similarity to the secreted chitinases ChiC of Serratia marcescens, ChiA of Vibrio harveyi, and ChiD of Bacillus circulans and consists of an activity domain and a chitin-binding domain, which are separated by a fibronectin type III domain. ChiC was able to bind and degrade colloidal chitin and was active on the artificial substrates carboxymethyl-chitin-Remazol Brilliant Violet and p-nitrophenyl-beta-D-N,N',N"-triacetylchitotriose, but not on p-nitrophenyl-beta-D-N-acetylglucosamine, indicating that it is an endochitinase. Expression of the chiC gene appears to be regulated by the quorum-sensing system of P. aeruginosa, since this gene was not expressed in a lasIR vsmI mutant. After overnight growth, the majority of the ChiC produced was found intracellularly, whereas only small amounts were detected in the culture medium. However, after several days, the cellular pool of ChiC was largely depleted, and the protein was found in the culture medium. This release could not be ascribed to cell lysis. Since ChiC did not appear to be secreted via any of the known secretion systems, a novel secretion pathway seems to be involved.
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Affiliation(s)
- J Folders
- Department of Molecular Microbiology, Institute of Biomembranes, Utrecht University, Utrecht, The Netherlands
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7
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Abstract
Elastase of Pseudomonas aeruginosa is synthesized as a preproenzyme. After propeptide-mediated folding in the periplasm, the proenzyme is autoproteolytically processed, prior to translocation of both the mature enzyme and the propeptide across the outer membrane. The formation of the two disulfide bonds present in the mature enzyme was examined by studying the expression of the wild-type enzyme and of alanine for cysteine mutant derivatives in the authentic host and in dsb mutants of Escherichia coli. It appeared that the two disulfide bonds are formed successively. First, DsbA catalyzes the formation of the disulfide bond between Cys-270 and Cys-297 within the proenzyme. This step is essential for the subsequent autoproteolytic processing to occur. The second disulfide bond between Cys-30 and Cys-57 is formed more slowly and appears to be formed after processing of the proenzyme, and its formation is catalyzed by DsbA as well. This second disulfide bond appeared to be required for the full proteolytic activity of the enzyme and contributes to its stability.
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Affiliation(s)
- P Braun
- Department of Molecular Cell Biology, Utrecht University, Padualaan 8, 3584 CH, Utrecht, The Netherlands
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8
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Chabeaud P, de Groot A, Bitter W, Tommassen J, Heulin T, Achouak W. Phase-variable expression of an operon encoding extracellular alkaline protease, a serine protease homolog, and lipase in Pseudomonas brassicacearum. J Bacteriol 2001; 183:2117-20. [PMID: 11222613 PMCID: PMC95110 DOI: 10.1128/jb.183.6.2117-2120.2001] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2000] [Accepted: 12/14/2000] [Indexed: 11/20/2022] Open
Abstract
The rhizobacterium Pseudomonas brassicacearum forms phenotypic variants which do not show extracellular protease and lipase activity. The operon encoding these enzymes, a serine protease homolog, and a type I secretion machinery was characterized. Transcriptional lacZ gene fusions revealed that the expression of the operon is under the control of phase variation.
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Affiliation(s)
- P Chabeaud
- CEA/Cadarache, DSV-DEVM, Laboratoire d'Ecologie Microbienne de la Rhizosphère, UMR 163 CNRS-CEA, F-13108 Saint-Paul-lez-Durance, France
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9
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Abstract
Gram-negative bacteria have developed a variety of secretion pathways to secrete toxins and enzymes into the extracellular medium. These pathways are very different with respect to their functional mechanism and complexity, and each system has its own advantages and limitations, regarding the number, size, folding state and fate of their substrates. Pseudomonas aeruginosa secretes many different proteins into the extracellular medium, using at least four secretion pathways. Most of the exoproteins are secreted via the type II system, composed of the 12 Xcp proteins. The only outer membrane protein of the system, XcpQ, belongs to a large family of proteins, designated secretins, which participate in a variety of different transport processes. Other Xcp proteins, XcpT-X, show homology to the subunits of the retractile type IV pili. Further analogies between the type II system and the assembly of retractile pili suggest a mechanism for type II secretion, in which a pilus-like structure, composed of XcpT-X, facilitates the transport of exoproteins through the channel formed by the secretin XcpQ.
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Affiliation(s)
- M Koster
- Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, The Netherlands
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10
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Abstract
Most lipases of Gram-negative bacteria require a lipase-specific foldase (Lif) in order to fold in the periplasm into their active, protease-resistant conformation prior to their secretion. The periplasmic domain of the Lif (amino acids 44-353) of Burkholderia glumae was purified as a His-tagged protein, and its function in the folding of lipase was studied in vitro. Refolding of the denatured lipase into its active conformation was dependent on the presence of the Lif. Circular dichroism revealed that the lipase refolded in the absence of Lif into a form with a native-like conformation, which was more stable against heat-induced denaturation than the native form, but was enzymatically inactive. This form of the protein could be activated by adding Lif after several hours, which demonstrates that the function of this chaperone is to help lipase to overcome an energetic barrier in the productive folding pathway rather than to prevent it from entering a non-productive pathway. The Lif was shown to interact with the native lipase in protease-protection experiments as well as by affinity chromatography, consistent with a role of the Lif late in the folding process. These results demonstrate that the Lif functions in a way analogous to the propeptides of many bacterial proteases and indicate that the amino acid sequence of the lipase does not contain all the information required for the protein to adopt its three-dimensional structure.
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Affiliation(s)
- M El Khattabi
- Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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11
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Abstract
One of the major proteins secreted by Pseudomonas aeruginosa is a 43-kDa protein, which is cleaved by elastase into smaller fragments, including a 30-kDa and a 23-kDa fragment. The N-terminal 23-kDa fragment was previously suggested as corresponding to a staphylolytic protease and was designated LasD (S. Park and D. R. Galloway, Mol. Microbiol. 16:263-270, 1995). However, the sequence of the gene encoding this 43-kDa protein revealed that the N-terminal half of the protein is homologous to the chitin-binding proteins CHB1 of Streptomyces olivaceoviridis and CBP21 of Serratia marcescens and to the cellulose-binding protein p40 of Streptomyces halstedii. Furthermore, a short C-terminal fragment shows homology to a part of chitinase A of Vibrio harveyi. The full-length 43-kDa protein could bind chitin and was thereby protected against the proteolytic activity of elastase, whereas the degradation products did not bind chitin. The purified 43-kDa chitin-binding protein had no staphylolytic activity, and comparison of the enzymatic activities in the extracellular medium of a wild-type strain and a chitin-binding protein-deficient mutant indicated that the 43-kDa protein supports neither chitinolytic nor staphylolytic activity. We conclude that the 43-kDa protein, which was found to be produced by many clinical isolates of P. aeruginosa, is a chitin-binding protein, and we propose to name it CbpD (chitin-binding protein D).
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Affiliation(s)
- J Folders
- Department of Molecular Microbiology and Institute of Biomembranes, Utrecht University, 3584 CH Utrecht, The Netherlands
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12
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Brok R, Van Gelder P, Winterhalter M, Ziese U, Koster AJ, de Cock H, Koster M, Tommassen J, Bitter W. The C-terminal domain of the Pseudomonas secretin XcpQ forms oligomeric rings with pore activity. J Mol Biol 1999; 294:1169-79. [PMID: 10600375 DOI: 10.1006/jmbi.1999.3340] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The Pseudomonas secretin XcpQ forms an oligomeric complex, which is involved in the translocation of proteins across the outer membrane via the type II secretion pathway. Pseudomonas aeruginosa produces only small amounts of this complex, 50 to 100 copies per bacterium, and overexpression is lethal to these cells. However, overexpression of Pseudomonas alcaligenes XcpQ could be achieved in the P. alcaligenes mutant strain 537. Protease protection experiments with P. alcaligenes XcpQ showed that the C-terminal domain of XcpQ, which is conserved in all the different members of the secretin family, is largely resistant to proteinase K. This protease-resistant fragment is embedded in the membrane and remains a stable complex, indicating that this domain is involved in complex formation. Both the intact and the protease-protected XcpQ complex showed a tendency to form two-dimensional crystal-like structures. Electron microscopic analysis of these structures showed that the overall oligomeric rings of the intact and of the protease-resistant complex are highly similar. The central cavity of the intact XcpQ complex contains structured mass. Both the intact and the protease-protected XcpQ complex showed pore-forming activity in planar lipid bilayers, consistent with their role as a translocation channel. However, the single-channel conductances observed were not uniform. Together, these results demonstrate that the C-terminal secretin homology domain of XcpQ is the structural domain that forms the channel through which macromolecules are being transported.
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Affiliation(s)
- R Brok
- Department of Molecular Microbiology, Utrecht University, The Netherlands
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13
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El Khattabi M, Ockhuijsen C, Bitter W, Jaeger KE, Tommassen J. Specificity of the lipase-specific foldases of gram-negative bacteria and the role of the membrane anchor. Mol Gen Genet 1999; 261:770-6. [PMID: 10394914 DOI: 10.1007/s004380050020] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
Abstract
Folding of lipases that are secreted by Pseudomonads and other gram-negative bacteria via the type II secretion pathway is facilitated by dedicated chaperones, called lipase-specific foldases (Lifs). Lifs are membrane-anchored proteins with a large periplasmic domain. The functional interaction between the Lif and its cognate lipase is specific, since the Pseudomonas aeruginosa Lif was found not to substitute for Lifs from Burkholderia glumae or Acinetobacter calcoaceticus. However, the P. aeruginosa Lif was able to activate the lipase from the closely related species P. alcaligenes. Hybrid proteins constructed from parts of the P. aeruginosa and B. glumae Lifs revealed that the C-terminal 138 amino acids of the B. glumae Lif determine the specificity of the interaction with the cognate lipase. Furthermore, the periplasmic domain of the B. glumae Lif was functional when cloned in frame with a cleavable signal sequence, which demonstrates that the membrane anchor is not essential for Lif function in vivo. However, the recombinant Lif was released into the medium, indicating that the function of the membrane anchor is to prevent secretion of the Lif together with the lipase.
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Affiliation(s)
- M El Khattabi
- Department of Molecular Microbiology, Utrecht University, The Netherlands.
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14
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Affiliation(s)
- W Bitter
- Dept of Molecular Microbiology, Utrecht University, The Netherlands.
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15
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Abstract
Elastase of Pseudomonas aeruginosa is synthesized as a preproenzyme. The signal sequence is cleaved off during transport across the inner membrane and, in the periplasm, proelastase is further processed. We demonstrate that the propeptide and the mature elastase are both secreted but that the propeptide is degraded extracellularly. In addition, reduction of the extracellular proteolytic activity led to the accumulation of unprocessed forms of LasA and LasD in the extracellular medium, which shows that these enzymes are secreted in association with their propeptides. Furthermore, a hitherto undefined protein with homology to a Streptomyces griseus aminopeptidase accumulated under these conditions.
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Affiliation(s)
- P Braun
- Department of Molecular Cell Biology, Utrecht University, The Netherlands
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16
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Borst P, Bitter W, Blundell PA, Chaves I, Cross M, Gerrits H, van Leeuwen F, McCulloch R, Taylor M, Rudenko G. Control of VSG gene expression sites in Trypanosoma brucei. Mol Biochem Parasitol 1998; 91:67-76. [PMID: 9574926 DOI: 10.1016/s0166-6851(97)00184-9] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Antigenic variation in African trypanosomes continues to be one of the most elaborate and intriguing strategies ever devised by a protozoan parasite to avoid complete destruction by the immune defense of its mammalian host. Here we review some of the recent advances in our understanding of this strategy, concentrating on (unpublished) work from our laboratory.
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Affiliation(s)
- P Borst
- Division of Molecular Biology, The Netherlands Cancer Institute, Amsterdam
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17
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Abstract
Trypanosoma brucei is a unicellular parasite transmitted between African mammals by tsetse flies. T. brucei multiplies freely in the bloodstream of many different mammals, and survives by antigenic variation of the main component of its surface coat, variant surface glycoprotein (VSG). Trypanosomes take up transferrin through a heterodimeric transferrin receptor, the genes for which are expressed in telomeric expression sites along with the VSG gene. There are up to 20 of these expression sites per trypanosome nucleus, but usually only one is active at a time. Different expression sites encode transferrin receptors that are similar but not identical. Here we show that these small differences between transferrin receptors can have profound effects on the binding affinity for transferrins from different mammals, and on the ability of trypanosomes to grow in the sera of these mammals. Our results suggest that the ability to switch between different transferrin-receptor genes allows T. brucei to cope with the large sequence diversity in the transferrins of its hosts.
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Affiliation(s)
- W Bitter
- The Netherlands Cancer Institute, Division of Molecular Biology, Amsterdam
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18
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Bitter W, Koster M, Latijnhouwers M, de Cock H, Tommassen J. Formation of oligomeric rings by XcpQ and PilQ, which are involved in protein transport across the outer membrane of Pseudomonas aeruginosa. Mol Microbiol 1998; 27:209-19. [PMID: 9466268 DOI: 10.1046/j.1365-2958.1998.00677.x] [Citation(s) in RCA: 191] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Pseudomonas aeruginosa is able to translocate proteins across both membranes of the cell envelope. Many of these proteins are transported via the type II secretion pathway and adopt their tertiary conformation in the periplasm, which implies the presence of a large transport channel in the outer membrane. The outer membrane protein, XcpQ, which is involved in transport of folded proteins across the outer membrane of P. aeruginosa, was purified as a highly stable homomultimer. Insertion and deletion mutagenesis of xcpQ revealed that the C-terminal part of XcpQ is sufficient for the formation of the multimer. However, linker insertions in the N-terminal part can disturb complex formation completely. Furthermore, complex formation is strictly correlated with lethality, caused by overexpression of xcpQ. Electron microscopic evaluation of the XcpQ multimers revealed large, ring-shaped structures with an apparent central cavity of 95 A. Purified PilQ, a homologue of XcpQ involved in the biogenesis of type IV pili, formed similar structures. However, the apparent cavity formed by PilQ was somewhat smaller, 53 A. The size of this cavity could allow for the transport of intact type IV pili.
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Affiliation(s)
- W Bitter
- Department of Molecular Cell Biology and Institute of Biomembranes, Utrecht University, The Netherlands.
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19
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Koster M, Bitter W, de Cock H, Allaoui A, Cornelis GR, Tommassen J. The outer membrane component, YscC, of the Yop secretion machinery of Yersinia enterocolitica forms a ring-shaped multimeric complex. Mol Microbiol 1997; 26:789-97. [PMID: 9427408 DOI: 10.1046/j.1365-2958.1997.6141981.x] [Citation(s) in RCA: 177] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The YscC protein of Yersinia enterocolitica is essential for the secretion of anti-host factors, called Yops, into the extracellular environment. It belongs to a family of outer membrane proteins, collectively designated secretins, that participate in a variety of transport processes. YscC has been shown to exist as a stable oligomeric complex in the outer membrane. The production of the YscC complex is regulated by temperature and is reduced in strains carrying mutations in the yscN-U operon or in the virG gene. The VirG lipoprotein was shown to be required for efficient targeting of the complex to the outer membrane. Electron microscopy revealed that purified YscC complexes form ring-shaped structures of approximately 20 nm with an apparent central pore. Because of the architecture of the multimer, YscC appears to represent a novel type of channel-forming proteins in the bacterial outer membrane.
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Affiliation(s)
- M Koster
- Microbial Pathogenesis Unit, International Institute of Cellular and Molecular Pathology and Faculté de Médecine, Université Catholique de Louvain, Brussels, Belgium.
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20
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Koster M, Ovaa W, Bitter W, Weisbeek P. Multiple outer membrane receptors for uptake of ferric pseudobactins in Pseudomonas putida WCS358. Mol Gen Genet 1995; 248:735-43. [PMID: 7476877 DOI: 10.1007/bf02191714] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Under iron limitation Pseudomonas putida WCS358 produces a fluorescent siderophore, pseudobactin 358, which, after complexing iron, is transported back into the cell via the specific outer membrane receptor PupA. In addition, this strain has the capacity to take up iron via a large variety of siderophores produced by other fluorescent pseudomonads. Putative receptor genes for such siderophores were identified in the chromosome of strain WCS358 by PCR using primers matching two domains conserved in four ferric pseudobactin receptors, including PupA. Eleven amplification products within the expected size range were obtained. Sequence analysis confirmed that the products were derived from genes encoding outer membrane receptors. Two complete receptor genes were isolated from a genomic library of P. putida WCS358. Both protein products are involved in the transport of a limited number of specific ferric pseudobactins. These results indicate that the ability of P. putida WCS358 to exploit many different heterologous pseudobactins is related to the presence of multiple outer membrane receptor proteins.
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Affiliation(s)
- M Koster
- Department of Molecular Cell Biology, Utrecht University, The Netherlands
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21
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Affiliation(s)
- P Borst
- The Netherlands Cancer Institute, Division of Molecular Biology, Amsterdam
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22
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Bitter W, van Leeuwen IS, de Boer J, Zomer HW, Koster MC, Weisbeek PJ, Tommassen J. Localization of functional domains in the Escherichia coli coprogen receptor FhuE and the Pseudomonas putida ferric-pseudobactin 358 receptor PupA. Mol Gen Genet 1994; 245:694-703. [PMID: 7830717 DOI: 10.1007/bf00297276] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Transport of ferric-siderophores across the outer membrane of gram-negative bacteria is mediated by specific outer membrane receptors. To localize the substrate-binding domain of the ferric-pseudobactin 358 receptor, PupA, of Pseudomonas putida WCS358, we constructed chimeric receptors in which different domains of PupA were replaced by the corresponding domains of the related ferric-pseudobactin receptors PupB and PupX, or the coprogen receptor FhuE of Escherichia coli. None of the chimeric proteins composed of pseudobactin receptor domains facilitated growth on any of the original substrates, or they showed only an extremely low efficiency. However, these receptors enabled cells of Pseudomonas BN8 to grow on media supplemented with uncharacterized siderophore preparations. These siderophore preparations were isolated from the culture supernatant of WCS358 cells carrying plasmids that contain genes of Pseudomonas B10 required for the biosynthesis of pseudobactin B10. Hybrid proteins that contained at least the amino-terminal 516 amino acids of mature FhuE were active as a receptor for coprogen and interacted with the E. coli TonB protein. A chimeric PupA-FhuE protein, containing the amino-terminal 94 amino acids of mature PupA, was also active as a coprogen receptor, but only in the presence of Pseudomonas TonB. It is concluded that the carboxy-terminal domain of ferric-pseudobactin receptors is important, but not sufficient, for ligand interaction, whereas binding of coprogen by the FhuE receptor is not dependent on this domain. Apparently, the ligand-binding sites of different receptors are located in different regions of the proteins. Furthermore, species-specific TonB binding by the PupA receptor is dependent on the amino-terminal domain of the receptor.
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Affiliation(s)
- W Bitter
- Department of Molecular Cell Biology, Utrecht University, The Netherlands
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23
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Koster M, van Klompenburg W, Bitter W, Leong J, Weisbeek P. Role for the outer membrane ferric siderophore receptor PupB in signal transduction across the bacterial cell envelope. EMBO J 1994; 13:2805-13. [PMID: 8026465 PMCID: PMC395160 DOI: 10.1002/j.1460-2075.1994.tb06574.x] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
The outer membrane protein PupB of Pseudomonas putida WCS358 facilitates transport of iron complexed to the siderophores pseudobactin BN8 and pseudobactin BN7 into the cell. Its synthesis is induced by the presence of these specific siderophores under iron limitation. The signal transduction pathway regulating siderophore-dependent expression of pupB was shown to consist of two regulatory proteins, PupI and PupR, and the PupB receptor itself. Mutational analysis of the regulatory genes suggested that PupI acts as a positive regulator of pupB transcription, whereas PupR modifies PupI activity dependent on the presence of pseudobactin BN8. PupI and PupR do not share homology with the classical bacterial two-component systems but display significant similarity to the FecI and FecR proteins of Escherichia coli involved in regulation of ferric dicitrate transport. The function of the PupB receptor in pupB regulation was studied by the use of chimeric receptor proteins composed of PupB and the ferric pseudobactin 358 receptor PupA. This experiment revealed that PupB is involved in the initiation of the signal transduction pathway, implying a so far unique role for an outer membrane protein in signal transduction.
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Affiliation(s)
- M Koster
- University of Utrecht, Department of Molecular Cell Biology, The Netherlands
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24
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Ligtenberg MJ, Bitter W, Kieft R, Steverding D, Janssen H, Calafat J, Borst P. Reconstitution of a surface transferrin binding complex in insect form Trypanosoma brucei. EMBO J 1994; 13:2565-73. [PMID: 8013456 PMCID: PMC395130 DOI: 10.1002/j.1460-2075.1994.tb06546.x] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In the bloodstream of the mammalian host, Trypanosoma brucei takes up host transferrin by means of a high-affinity uptake system, presumably a transferrin receptor. Transferrin-binding activity is seen in the flagellar pocket and is absent in insect form trypanosomes. By transfection we have reconstituted a transferrin-binding complex in insect form trypanosomes. Formation of this complex requires the products of two genes that are part of a variant surface glycoprotein expression site, expression site-associated gene (ESAG) 6 (encoding a protein with GPI-anchor) and ESAG 7 (encoding a protein without any obvious membrane attachment). This complex can be precipitated by transferrin-Sepharose and by an antibody directed only against the ESAG 6 protein. Transfection of ESAG 6 or 7 alone did not result in transferrin binding. In the transfected trypanosomes, the products of ESAG 6 alone and the combination of ESAG 6 and 7 did not exclusively localize to the flagellar pocket, but were present all over the surface of the trypanosome. The reconstituted transferrin-binding complex also did not result in the uptake of transferrin. Additional proteins present in bloodstream trypanosomes, but not in sufficient amounts in insect form trypanosomes, may therefore be required for the correct routing of the transferrin-binding complex to the flagellar pocket, and for its rapid internalization after ligand binding.
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Affiliation(s)
- M J Ligtenberg
- The Netherlands Cancer Institute, Division of Molecular Biology, Amsterdam
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25
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Raaijmakers JM, Bitter W, Punte HL, Bakker PA, Weisbeek PJ, Schippers B. Siderophore receptor PupA as a marker to monitor wild-type Pseudomonas putida WCS358 in natural environments. Appl Environ Microbiol 1994; 60:1184-90. [PMID: 8017914 PMCID: PMC201457 DOI: 10.1128/aem.60.4.1184-1190.1994] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
For application of genetically engineered fluorescent Pseudomonas spp., specific markers are required for monitoring of wild-type Pseudomonas strains and their genetically modified derivatives in natural environments. In this study, the specific siderophore receptor PupA of plant growth-promoting Pseudomonas putida WCS358 was used as a marker to monitor wild-type strain WCS358. After introduction into natural soil and rhizosphere environments, strain WCS358 could be recovered efficiently on a medium amended with 300 microM pseudobactin 358. Although low population densisties of indigenous pseudomonads (less than or equal to 10(3)/g of soil or root) were recovered on the pseudobactin 358-amended medium, subsequent agglutination assays with a WCS358-specific polyclonal antiserum enabled accurate monitoring of populations of wild-type strain WCS358 over a range of approximately 10(3) to 10(7) CFU/g of soil or root. Genetic analysis of the background population by PCR and Southern hybridization revealed that natural occurrence of the pupA gene was limited to a very small number of indigenous Pseudomonas spp. which are very closely related to P. putida WCS358. The PupA marker system enabled the study of differences in rhizosphere colonization among wild-type strain WCS358, rifampin-resistant derivative WCS358rr, and Tn5 mutant WCS358::xylE. Chromosomally mediated rifampin resistance did not affect the colonizing ability of P. putida WCS358. However, Tn5 mutant WCS358::xylE colonized the radish rhizosphere significantly less than did its parental strain.
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Affiliation(s)
- J M Raaijmakers
- Department of Plant Ecology and Evolutionary Biology, Utrecht University, The Netherlands
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26
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Bitter W, Tommassen J, Weisbeek PJ. Identification and characterization of the exbB, exbD and tonB genes of Pseudomonas putida WCS358: their involvement in ferric-pseudobactin transport. Mol Microbiol 1993; 7:117-30. [PMID: 8437515 DOI: 10.1111/j.1365-2958.1993.tb01103.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Catechol-cephalosporins are siderophore-like antibiotics which are taken up by cells of Pseudomonas putida WCS358 via the ferric-siderophore transport pathway. Mutants of strain WCS358 were isolated that are resistant to high concentrations of these antibiotics. These mutants failed to grow under iron-limiting conditions, and could not utilize different ferric-siderophores. The mutants fall in three complementation groups. The nucleotide sequence determination identified three contiguous open reading frames, which were homologous to the exbB, exbD and tonB genes of Escherichia coli respectively. The deduced amino acid sequence of P. putida ExbB showed 58.6% homology with its E. coli homologue, but, unlike the E. coli protein, it has a N-terminal extension of 91 amino acids. The ExbD proteins are 64.8% homologous, whereas the TonB proteins only show 27.7% homology. The P. putida exbB gene could complement an E. coli exbB mutation, but the TonB proteins were not interchangeable between the species. It is concluded that P. putida WCS358 contains an energy-coupling system between the membranes, for active transport across the outer membrane, which is comprised of a TonB-like energy-transducing protein and two accessory proteins. This system is similar to, but not completely compatible with, the E. coli system.
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Affiliation(s)
- W Bitter
- Department of Molecular Cell Biology, University of Utrecht, The Netherlands
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27
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Bitter W, Marugg JD, de Weger LA, Tommassen J, Weisbeek PJ. The ferric-pseudobactin receptor PupA of Pseudomonas putida WCS358: homology to TonB-dependent Escherichia coli receptors and specificity of the protein. Mol Microbiol 1991; 5:647-55. [PMID: 1646376 DOI: 10.1111/j.1365-2958.1991.tb00736.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The initial step in the uptake of iron via ferric pseudobactin by the plant-growth-promoting Pseudomonas putida strain WCS358 is binding to a specific outer-membrane protein. The nucleotide sequence of the pupA structural gene, which codes for a ferric pseudobactin receptor, was determined. It contains a single open reading frame which potentially encodes a polypeptide of 819 amino acids, including a putative N-terminal signal sequence of 47 amino acids. Significant homology, concentrated in four boxes, was found with the TonB-dependent receptor proteins of Escherichia coli. The pupA mutant MH100 showed a residual efficiency of 30% in the uptake of 55Fe3+ complexed to pseudobactin 358, whereas the iron uptake of four other pseudobactins was not reduced at all. Cells of strain WCS374 supplemented with the pupA gene of strain WCS358 could transport ferric pseudobactin 358 but showed no affinity for three other pseudobactins. It is concluded that PupA is a specific receptor for ferric pseudobactin 358, and that strain WCS358 produces at least one other receptor for other pseudobactins.
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Affiliation(s)
- W Bitter
- Department of Molecular Cell Biology, University of Utrecht, The Netherlands
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28
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Bitter W. Localization and handling of failed fuel subassemblies in sodium-cooled fast breeder reactors / Lokalisierung und Behandlung defekter Kernelemente in schnellen natriumgekühlten Brutreaktoren. KERNTECHNIK 1991. [DOI: 10.1515/kern-1991-560219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Hård K, Bitter W, Kamerling JP, Vliegenthart JF. O-mannosylation of recombinant human insulin-like growth factor I (IGF-I) produced in Saccharomyces cerevisiae. FEBS Lett 1989; 248:111-4. [PMID: 2656293 DOI: 10.1016/0014-5793(89)80442-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
A glycosylated form of recombinant human insulin-like growth factor I (IGF-I) expressed in Saccharomyces cerevisiae was shown to contain mannose as the only carbohydrate constituent. All oligosaccharide chains of the glycoprotein could be released by mild alkaline treatment, and separated from the protein by gel-permeation chromatography on Bio-Gel P-2. The structures of these O-linked carbohydrate chains were determined by 500-MHz 1H-NMR spectroscopy, affording the disaccharide Man alpha 1-2Man as the major component and the tetrasaccharide Man alpha 1-3Man alpha 1-2Man alpha 1-2Man as a minor component. Reference oligosaccharides were prepared from mannoproteins released from the cell wall of S. cerevisiae X2180 (alpha-wild type). In addition to previously reported structures, ranging from mannose to mannotetraose, the pentasaccharide Man alpha 1-3Man alpha 1-3Man alpha 1-2Man alpha 1-2Man was identified in the cell wall mannoprotein.
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Affiliation(s)
- K Hård
- Department of Bio-Organic Chemistry, Utrecht University, The Netherlands
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Bosch D, de Boer P, Bitter W, Tommassen J. The role of the positively charged N-terminus of the signal sequence of E. coli outer membrane protein PhoE in export. Biochim Biophys Acta 1989; 979:69-76. [PMID: 2644971 DOI: 10.1016/0005-2736(89)90524-5] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Signal sequences of prokaryotic exported proteins have a dipolar character due to positively charged amino-acid residues at the N-terminus and to a preferentially negatively charged region around the cleavage site. The role of the two lysine residues at the N-terminus of the signal sequence of outer membrane protein PhoE of E. coli-K12 was investigated. Replacement of both of these residues by aspartic acid slightly affected the kinetics of protein translocation in vivo. This export defect, which was observed only when PhoE was overproduced, could not be suppressed by the prlA4 mutation, which has been shown to restore export defects caused by alterations in the hydrophobic core of the signal sequences of various exported proteins. In an in vitro translocation assay, the export defect was more pronounced. Replacement of both lysines by uncharged residues did not disturb the kinetics of protein export in vivo. In the in vitro assay, an extraordinarily efficient processing was detected upon incubation of this precursor with inverted cytoplasmic membrane vesicles. However, this efficient processing was not accompanied by more efficient translocation of the protein. We conclude that the positively charged residues at the N-terminus of the signal sequence are not essential for protein export, but contribute to the efficiency of the process.
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Affiliation(s)
- D Bosch
- Department of Molecular Cell Biology, State University of Utrecht, The Netherlands
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