| 11. |
- Larsson, Jonas, et al.
(författare)
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YjbH is a novel negative effector of the disulphide stress regulator,Spx, in Bacillus subtilis.
- 2007
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 66:3, s. 669-684
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Tidskriftsartikel (refereegranskat)abstract
- In the soil bacterium Bacillus subtilis Spx is a key regulator that controls expression, positively or negatively, of several genes in response to certain oxidative stresses that lead to the formation of unwanted disulphide bonds. Here we characterized the yjbH gene and show that it encodes a novel effector of Spx. The yjbH gene is part of the yjbIH operon that encodes a truncated haemoglobin (YjbI) and a predicted 34 kDa cytosolic protein of unknown function (YjbH). Deletion of yjbIH or yjbH has pleiotropic effects and affects growth, sporulation and competence development. Cells lacking yjbIH display a reduced sensitivity to the thiol oxidant diamide and show an apparent down- or upregulation of several transcripts that belong to the Spx regulon. Twenty-two suppressor mutations that bypass the defects conferred by yjbH were isolated. These mutations were identified as six deletions, three nonsense and 11 missense substitutions in the spx gene. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis showed that mutations in yjbIH or yjbH do not affect the level of spx transcription. The combined data from the present work show that strains lacking yjbIH or yjbH overproduce Spx under unperturbed growth. The elevated Spx concentration cannot be attributed to an increased spx expression but is likely to result from control at the post-transcriptional level. YjbH is proposed to affect the cellular concentration of Spx by modulating proteolysis via the ClpXP protease.
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| 12. |
- Lind, Peter A, et al.
(författare)
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Compensatory gene amplification restores fitness after inter-species gene replacements
- 2010
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Ingår i: Molecular Microbiology. - : Wiley. - 0950-382X .- 1365-2958. ; 75:5, s. 1078-1089
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Tidskriftsartikel (refereegranskat)abstract
- Genes introduced by gene replacements and other types of horizontal gene transfer (HGT) represent a significant presence in many archaeal and eubacterial genomes. Most alien genes are likely to be neutral or deleterious upon arrival and their long-term persistence may require a mechanism that improves their selective contribution. To examine the fate of inter-species gene replacements, we exchanged three native S. typhimurium genes encoding ribosomal proteins with orthologues from various other microbes. The results show that replacement of each of these three genes reduces fitness to such an extent that it would provide an effective barrier against inter-species gene replacements in eubacterial populations. However, these fitness defects could be partially ameliorated by gene amplification that augmented the dosage of the heterologous proteins. This suggests that suboptimal expression is a common fitness constraint for inter-species gene replacements, with fitness costs conferred by either a lower expression level of the alien protein compared with the native protein or a requirement for an increased amount of the alien protein to maintain proper function. Our findings can explain the observation that duplicated genes are over-represented among horizontally transferred genes, and suggest a potential coupling between compensatory gene amplification after HGT and the evolution of new genes.
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| 13. |
- Liu, Yiming, et al.
(författare)
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Penicillin-binding protein SpoVD disulfide is a target for StoA in Bacillus subtilis forespores.
- 2010
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 75:1, s. 46-60
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Tidskriftsartikel (refereegranskat)abstract
- Summary The bacterial endospore is a dormant and heat-resistant form of life. StoA (SpoIVH) in Bacillus subtilis is a membrane-bound thioredoxin-like protein involved in endospore cortex synthesis. It is proposed to reduce disulfide bonds in hitherto unknown proteins in the inter-membrane compartment of developing forespores. Starting with a bioinformatic analysis combined with mutant studies we identified the sporulation-specific, high molecular weight, class B penicillin-binding protein SpoVD as a putative target for StoA. We then demonstrate that SpoVD is a membrane-bound protein with two exposed redox-active cysteine residues. Structural modelling of SpoVD, based on the well characterized orthologue PBP2x of Streptococcus pneumoniae, confirmed that a disulfide bond can form close to the active site of the penicillin-binding domain restricting access of enzyme substrate or functional association with other cortex biogenic proteins. Finally, by exploiting combinations of mutations in the spoVD, stoA and ccdA genes in B. subtilis cells, we present strong in vivo evidence that supports the conclusion that StoA functions to specifically break the disulfide bond in the SpoVD protein in the forespore envelope. The findings contribute to our understanding of endospore biogenesis and open a new angle to regulation of cell wall synthesis and penicillin-binding protein activity.
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| 14. |
- Nilsson, Maria, et al.
(författare)
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The antibacterial activity of peptides derived from human beta-2 glycoprotein I is inhibited by protein H and M1 protein from Streptococcus pyogenes.
- 2008
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 67:3, s. 482-492
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Tidskriftsartikel (refereegranskat)abstract
- During the last years, the importance of antibacterial peptides has attracted considerable attention. We report here that peptides derived from the fifth domain of beta-2 glycoprotein I (beta(2)GPI), a human heparin binding plasma protein, have antibacterial activities against Gram-positive and Gram-negative bacteria. Streptococcus pyogenes, an important human pathogen that can survive and grow in human blood, has developed mechanisms to escape the attack by these peptides. Thus, protein H and M1 protein, two surface proteins of the highly pathogenic S. pyogenes AP1 strain, bind full-length beta(2)GPI and thereby prevent the processing of beta(2)GPI by proteases from polymorphonuclear neutrophils (PMNs) into antibacterial peptides. In addition, protein H and M1 protein, released from the bacterial cell wall by PMN-derived proteases, bind to, and inhibit the activity of, beta(2)GPI-derived antibacterial peptides. Taken together, the data suggest that the interaction between the streptococcal proteins and beta(2)GPI or beta(2)GPI-derived peptides presents a novel mechanism to resist an antibacterial attack by beta(2)GPI-cleavage products.
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| 15. |
- Piskur, Jure, et al.
(författare)
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Yeast genome sequencing: the power of comparative genomics
- 2004
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 53:2, s. 381-389
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Forskningsöversikt (refereegranskat)abstract
- For decades, unicellular yeasts have been general models to help understand the eukaryotic cell and also our own biology. Recently, over a dozen yeast genomes have been sequenced, providing the basis to resolve several complex biological questions. Analysis of the novel sequence data has shown that the minimum number of genes from each species that need to be compared to produce a reliable phylogeny is about 20. Yeast has also become an attractive model to study speciation in eukaryotes, especially to understand molecular mechanisms behind the establishment of reproductive isolation. Comparison of closely related species helps in gene annotation and to answer how many genes there really are within the genomes. Analysis of non-coding regions among closely related species has provided an example of how to determine novel gene regulatory sequences, which were previously difficult to analyse because they are short and degenerate and occupy different positions. Comparative genomics helps to understand the origin of yeasts and points out crucial molecular events in yeast evolutionary history, such as whole-genome duplication and horizontal gene transfer(s). In addition, the accumulating sequence data provide the background to use more yeast species in model studies, to combat pathogens and for efficient manipulation of industrial strains.
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| 16. |
- Rasmussen, Magnus, et al.
(författare)
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Proteolysis and its regulation at the surface of Streptococcus pyogenes.
- 2002
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 43:3, s. 537-544
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Forskningsöversikt (refereegranskat)abstract
- Pathogenic bacteria often produce proteinases that are believed to be involved in virulence. Moreover, several host defence systems depend on proteolysis, demonstrating that proteolysis and its regulation play an important role during bacterial infections. Here, we discuss how proteolytical events are regulated at the surface of Streptococcus pyogenes during infection with this important human pathogen. Streptococcus pyogenes produces proteinases, and host proteinases are produced and released as a result of the infection. Streptococcus pyogenes also recruits host proteinase inhibitors to its surface, suggesting that proteolysis is tightly regulated at the bacterial surface. We propose that the initial phase of a S. pyogenes infection is characterized by inhibition of proteolysis and complement activity at the bacterial surface. This is achieved mainly through binding of host proteinase inhibitors and complement regulatory proteins to bacterial surface proteins. In a later phase of the infection, massive proteolytic activity will release bacterial surface proteins and degrade human tissues, thus facilitating bacterial spread. These proteolytic events are regulated both temporally and spatially, and should influence virulence and the outcome of S. pyogenes infections.
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| 17. |
- Rasmussen, Magnus, et al.
(författare)
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Unique regulation of SclB - a novel collagen-like surface protein of Streptococcus pyogenes
- 2001
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 40:6, s. 1427-1438
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Tidskriftsartikel (refereegranskat)abstract
- Slipped-strand mispairing at sites containing so-called coding repeats (CRs) can lead to phase variation of surface proteins in Gram-negative bacteria. This mechanism, believed to contribute to virulence, has so far not been identified in a Gram-positive bacterium. In the genome of the Gram-positive human pathogen Streptococcus pyogenes, we identified pentanucleotide CRs within a putative signal sequence of an open reading frame (ORF) encoding a novel collagen-like surface protein, denoted SclB. In 12 S. pyogenes strains, the number of CRs in the sclB gene varied from three to 19, rendering the start codon in frame with the downstream ORF in four strains and out of frame in eight strains. A protein reacting with anti-SclB antibodies could only be solubilized from three strains, all containing an intact sclB gene. Variations in the number of CRs were observed within strains of the same M serotype and occurred during growth of S. pyogenes in fresh human blood, but not in medium. The SclB protein has a hypervariable N-terminal part, a collagen-like central part and a typical cell wall sorting sequence containing the LPXTGX motif. SclB is related to the collagen-like SclA and is, like SclA, involved in the adhesion of S. pyogenes bacteria to human cells. However, the Mga protein, known to upregulate sclA and several additional genes encoding virulence factors of S. pyogenes, downregulates sclB transcription. This observation and the potential of SclB to phase vary by slipped-strand mispairing emphasize the unique regulation of this novel S. pyogenes surface protein.
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| 18. |
- Sandin, Charlotta, et al.
(författare)
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Binding of human plasma proteins to Streptococcus pyogenes M protein determines the location of opsonic and non-opsonic epitopes
- 2006
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 59:1, s. 20-30
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Tidskriftsartikel (refereegranskat)abstract
- Antibodies directed against a pathogenic microorganism may recognize either protective or non-protective epitopes. Because antibodies elicited by a vaccine must be directed against protective epitopes, it is essential to understand the molecular properties that distinguish the two types of epitope. Here we analyse this problem for the antiphagocytic M protein of Streptococcus pyogenes, using the opsonizing capacity of antibodies to estimate their ability to confer protection in vivo. Our studies were focused on the M5 protein, which has three surface-exposed regions: the amino-terminal hypervariable region (HVR) and the B- and C-repeat regions. We first analysed the role of different M5 regions in phagocytosis resistance under non-immune conditions, employing chromosomal mutants expressing M5 proteins with internal deletions, and demonstrate that only the B-repeat region is essential for phagocytosis resistance. However, only antibodies to the HVR were opsonic. This apparent paradox could be explained by the ability of fibrinogen and albumin to specifically bind to the B- and C-repeats, respectively, causing inhibition of antibody binding under physiological conditions, while antibodies to the HVR could bind and promote deposition of complement. These data indicate that binding of human plasma proteins plays an important role in determining the location of opsonic and non-opsonic epitopes in streptococcal M protein.
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| 19. |
- Schmidtchen, Artur, et al.
(författare)
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Dermatan sulphate is released by proteinases of common pathogenic bacteria and inactivates antibacterial alpha-defensin
- 2001
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 39:3, s. 708-713
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Tidskriftsartikel (refereegranskat)abstract
- Defensins represent an evolutionarily conserved group of small peptides with potent antibacterial activities. We report here that extracellular proteinases secreted by the human pathogens Pseudomonas aeruginosa, Enterococcus faecalis and Streptococcus pyogenes release dermatan sulphate by degrading dermatan sulphate-containing proteoglycans, such as decorin. Dermatan sulphate was found to bind to neutrophil-derived alpha-defensin, and this binding completely neutralized its bactericidal activity. During infection, proteoglycan degradation and release of dermatan sulphate may therefore represent a previously unknown virulence mechanism, which could serve as a target for novel antibacterial strategies.
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| 20. |
- Singh, Birendra, et al.
(författare)
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Vitronectin binds to the head region of Moraxella catarrhalis ubiquitous surface protein A2 and confers complement-inhibitory activity.
- 2010
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Ingår i: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 75, s. 1426-1444
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Tidskriftsartikel (refereegranskat)abstract
- Summary The serum resistance of the common respiratory pathogen Moraxella catarrhalis is mainly dependent on ubiquitous surface proteins (Usp) A1 and A2 that interact with complement factor 3 (C3) and complement inhibitor C4b binding protein (C4BP) preventing the alternative and classical pathways of the complement system respectively. UspA2 also has the capacity to attract vitronectin that in turn binds C9 and hereby inhibits membrane attack complex (MAC) formation. We found UspA2 as a major vitronectin binding protein and hence the UspA2/vitronectin interaction was studied in detail. The affinity constant (K(D)) for vitronectin binding to UspA2 was 2.3 x 10(-8) M, and the N-terminal region encompassing residues UspA2 30-170 bound vitronectin with a K(D) of 7.9 x 10(-8) M. Electron microscopy verified that the active binding domain (UspA2(30-177)) was located at the head region of UspA2. Experiments with recombinantly expressed vitronectin also revealed that UspA2(30-177) bound to the C-terminal region of vitronectin residues 312-396. Finally, when human serum was pre-incubated with UspA2, bacteria showed significantly less serum resistance. Our study directly reveals the binding mode between the N-terminal domain of UspA2 and the C-terminal part of vitronectin and thus sheds light upon the mechanism of M. catarrhalis-dependent serum resistance.
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