Protein rib: a novel group B streptococcal cell surface protein that confers protective immunity and is expressed by most strains causing invasive infections.

Abstract

Snmmal~The group B Streptococcus, an important cause of invasive infections in the neonate, is dassified into four major serotypes (Ia, Ib, II, and III) based on the structure of the polysaccharide capsule. Since the capsule is a known virulence factor, it has been extensively studied, in particular in type III strains, which cause the majority of invasive infections. Two cell surface proteins, a and fl, have also been studied in detail since they confer protective immunity, but these proteins are usually not expressed by type III strains. We describe here a cell surface protein, designated protein Rib (resistance to proteases, immunity, group B), that confers protective immunity and is expressed by most strains of type III. Protein Rib was first identified as a distinct 95-kD protein in extracts of a type III strain, and was purified to homogeneity from that strain. Rabbit antiserum to protein Rib was used to demonstrate that it is expressed on the cell surface of 31 out of 33 type III strains, but only on 1 out of 25 strains representing the other three serotypes. Mouse protection tests showed that antiserum to protein Rib protects against lethal infection with three different strains expressing this antigen, including a strain representing a recently identified high virulence type III clone. Protein Rib is immunologicaUy unrelated to the e~ and fl proteins, but shares several features with the oe protein. Most importantly, the NH2-terminal amino acid sequences of the Rib and o~ proteins are identical at 6 out of 12 positions. In addition, both protein Rib and the a protein are relatively resistant to trypsin (and Rib is also resistant to pepsin) and both proteins vary greatly in size between different clinical isolates. Finally, both protein Rib and the a protein exhibit a regular ladderlike pattern in immunoblotting experiments, which may reflect a repetitive structure. Taken together, these data suggest that the Rib and ol proteins are members of a family of proteins with related structure and function. Since protein Rib confers protective immunity, it may be valuable for the development of a protein vaccine against the group B Streptococcus, an encapsulated bacterium.

StreptococcusAdherence and Colonization

“…A protein-based vaccine could, on the other hand, provide antigenic targets that are conserved across all GBS serotypes. Major surface proteins include the Alp family of proteins, e.g., ␣, Rib, R28, and Alp2 (357,571,572), that elicit protective immunity; ScpB C5a peptidase (96); ␤ protein that binds IgA and factor H (373, 374); Lmb (228,567); FbsA fibrinogenbinding protein (535); Sip (67, 385); LrrG (538); and CspA protease (221). Some of these proteins are promising vaccine candidates, but their potential for cross-protection is relatively unknown (279).…”

Induction of a Regulatory Phenotype in Human CD4+ T Cells by Streptococcal M Protein

“…25 and our unpublished data). The group B streptococcal Rib protein was purified from strain BM110 as described (26).…”

Investigation of the translation-initiation factor IF2 gene, infB, as a tool to study the population structure of Streptococcus agalactiae The EMBL accession numbers for the sequences reported in this paper are AJ003164 and AJ251493 to AJ251499.

“…available and intrapartum prophylactic treatment with antibiotics is used routinely in some countries (Schuchat, 1999). The polysaccharide capsule is recognized as a major virulence factor in S. agalactiae and, in addition, the bacterium may express a number of proteins including C5a peptidase, hyaluronidase, alpha-antigen or RIP, and beta-antigen that are potential virulence factors (Cleat & Timmis, 1987 ;Li et al, 1997 ;Pritchard & Lin, 1993 ;Sta/ lhammar-Carlemalm et al, 1993 ;Wexler et al, 1985). Differences in pathogenic potential among subpopulations of S. agalactiae have been disputed.…”