Dataset Information

Characterization of fibrinogen binding by glycoproteins Srr1 and Srr2 of Streptococcus agalactiae.

ABSTRACT: The serine-rich repeat glycoproteins of Gram-positive bacteria comprise a large family of cell wall proteins. Streptococcus agalactiae (group B streptococcus, GBS) expresses either Srr1 or Srr2 on its surface, depending on the strain. Srr1 has recently been shown to bind fibrinogen, and this interaction contributes to the pathogenesis of GBS meningitis. Although strains expressing Srr2 appear to be hypervirulent, no ligand for this adhesin has been described. We now demonstrate that Srr2 also binds human fibrinogen and that this interaction promotes GBS attachment to endothelial cells. Recombinant Srr1 and Srr2 bound fibrinogen in vitro, with affinities of KD = 2.1 × 10(-5) and 3.7 × 10(-6) M, respectively, as measured by surface plasmon resonance spectroscopy. The binding site for Srr1 and Srr2 was localized to tandem repeats 6-8 of the fibrinogen A? chain. The structures of both the Srr1 and Srr2 binding regions were determined and, in combination with mutagenesis studies, suggest that both Srr1 and Srr2 interact with a segment of these repeats via a "dock, lock, and latch" mechanism. Moreover, properties of the latch region may account for the increased affinity between Srr2 and fibrinogen. Together, these studies identify how greater affinity of Srr2 for fibrinogen may contribute to the increased virulence associated with Srr2-expressing strains.

SUBMITTER: Seo HS

PROVIDER: S-EPMC3861647 | biostudies-literature | 2013 Dec

REPOSITORIES: biostudies-literature

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Characterization of fibrinogen binding by glycoproteins Srr1 and Srr2 of Streptococcus agalactiae.

Seo Ho Seong HS Minasov George G Seepersaud Ravin R Doran Kelly S KS Dubrovska Ievgeniia I Shuvalova Ludmilla L Anderson Wayne F WF Iverson Tina M TM Sullam Paul M PM

The Journal of biological chemistry 20131028 50

The serine-rich repeat glycoproteins of Gram-positive bacteria comprise a large family of cell wall proteins. Streptococcus agalactiae (group B streptococcus, GBS) expresses either Srr1 or Srr2 on its surface, depending on the strain. Srr1 has recently been shown to bind fibrinogen, and this interaction contributes to the pathogenesis of GBS meningitis. Although strains expressing Srr2 appear to be hypervirulent, no ligand for this adhesin has been described. We now demonstrate that Srr2 also bi ...[more]

PMID: 24165132

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Project description:Serine-rich (Srr) proteins exposed at the surface of Gram-positive bacteria are a family of adhesins that contribute to the virulence of pathogenic staphylococci and streptococci. Lectin-binding experiments have previously shown that Srr proteins are heavily glycosylated. We report here the first mass-spectrometry analysis of the glycosylation of Streptococcus agalactiae Srr1. After Srr1 enrichment and trypsin digestion, potential glycopeptides were identified in collision induced dissociation spectra using X! Tandem. The approach was then refined using higher energy collisional dissociation fragmentation which led to the simultaneous loss of sugar residues, production of diagnostic oxonium ions and backbone fragmentation for glycopeptides. This feature was exploited in a new open source software tool (SpectrumFinder) developed for this work. By combining these approaches, 27 glycopeptides corresponding to six different segments of the N-terminal region of Srr1 [93-639] were identified. Our data unambiguously indicate that the same protein residue can be modified with different glycan combinations including N-acetylhexosamine, hexose, and a novel modification that was identified as O-acetylated-N-acetylhexosamine. Lectin binding and monosaccharide composition analysis strongly suggested that HexNAc and Hex correspond to N-acetylglucosamine and glucose, respectively. The same protein segment can be modified with a variety of glycans generating a wide structural diversity of Srr1. Electron transfer dissociation was used to assign glycosylation sites leading to the unambiguous identification of six serines and one threonine residues. Analysis of purified Srr1 produced in mutant strains lacking accessory glycosyltransferase encoding genes demonstrates that O-GlcNAcylation is an initial step in Srr1 glycosylation that is likely required for subsequent decoration with Hex. In summary, our data obtained by a combination of fragmentation mass spectrometry techniques associated to a new software tool, demonstrate glycosylation heterogeneity of Srr1, characterize a new protein modification, and identify six glycosylation sites located in the N-terminal region of the protein.

Project description:BACKGROUND: Binding of serum components by surface M-related proteins, encoded by the emm genes, in streptococci constitutes a major virulence factor in this important group of organisms. The present study demonstrates fibrinogen binding by S. iniae, a Lancefield non-typeable pathogen causing devastating fish losses in the aquaculture industry and an opportunistic pathogen of humans, and identifies the proteins involved and their encoding genes. RESULTS: Fibrinogen binding by S. iniae significantly reduced respiratory burst activity of barramundi peritoneal macrophages in primary cultures compared to BSA-treated or untreated controls, indicating a potentially important role for fibrinogen binding cell-surface proteins in avoiding phagocytic attack in fish. We describe a novel emm-like gene, simA, encoding a 57 kDa fibrinogen binding M-like protein in S. iniae. These SiM proteins and their corresponding tetrameric structures from some sequevar types (approximately 230 kDa) bound fibrinogen in Western blots. simA was most closely related (32% identity) to the demA gene of S. dysgalactiae. Genome walking and sequencing determined the genetic organization of the simA region had similarities to the mgrC regulon in GCS and to S. uberis. Moreover, a putative multigene regulator, mgx was orientated in the opposite direction to the simA gene in common with S. uberis, but contrary to findings in GAS and GCS. In GAS, diversity among emm-genes and consequent diversity of their M-related proteins results in substantial antigenic variation. However, an extensive survey of S. iniae isolates from diverse geographic regions and hosts revealed only three variants of the gene, with one sequevar accounting for all but two of the 50 isolates analysed. CONCLUSION: These proteins play a role in avoiding oxidative attack by phagocytic cells during infection of fish by S. iniae, but genetic diversity amongst these key surface proteins has not yet arisen. This lack of diversity coupled with a functional role in macrophage resistance suggests that these proteins may constitute important targets for future vaccines against S. iniae in fish.

Dataset Information

Characterization of fibrinogen binding by glycoproteins Srr1 and Srr2 of Streptococcus agalactiae.

Publications

Characterization of fibrinogen binding by glycoproteins Srr1 and Srr2 of Streptococcus agalactiae.

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