Abstract
The group B Streptococcus (GBS) causes the majority of life-threatening bacterial infections in newborn children. Most GBS strains isolated from such infections express a surface protein, designated Rib, that confers protective immunity and therefore is of interest for analysis of pathogenetic mechanisms. Sequence analysis demonstrated that Rib has an exceptionally long signal peptide (55 amino acid residues) and 12 repeats (79 amino acid residues each) that account for >80% of the sequence of the mature protein. The repeats are identical even at the DNA level, indicating that an efficient mechanism operates to maintain a highly repetitive structure in Rib. The structure of Rib is similar to that of alpha, a previously characterized surface protein that is common among GBS strains lacking Rib. However, highly purified preparations of Rib and alpha did not cross-react immunologically, although the two proteins show extensive amino acid residue identity (47% in the repeat region). When analyzed in Western blots, Rib and alpha give rise to a regularly spaced ladder pattern, apparently due to hydrolysis of acid-labile Asp-Pro bonds in the repeats. We conclude that Rib and alpha are members of a novel family of streptococcal surface proteins with unusual repetitive structure.
Highlights
Immunity, the first to be identified were two molecules designated ␣ and  [3, 7, 8], which have been extensively characterized (9 –14)
The processed form of protein Rib has a length of 1176 amino acid residues and a predicted molecular mass of 123 kDa
In this report we describe the nucleotide sequence of the streptococcal surface protein Rib and show that Rib together with the ␣ protein of group B Streptococcus (GBS) define a novel family of bacterial surface proteins
Summary
Immunity, the first to be identified were two molecules designated ␣ and  [3, 7, 8], which have been extensively characterized (9 –14). Protein Rib is of considerable interest for the analysis of pathogenetic mechanisms in GBS infections and for vaccine development. This situation motivates detailed biochemical and immunological characterization of protein Rib. Studies of protein Rib previously showed that it shares several properties with the ␣ protein [6]. Many children are exposed to this bacterium at birth, when they may be colonized by GBS present in the vaginal flora of the mother In most cases such colonization does not cause disease, but a minority of newborns fall seriously ill after birth due to invasive GBS infection.
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