M. Wastfelt et al., IDENTIFICATION OF A FAMILY OF STREPTOCOCCAL SURFACE-PROTEINS WITH EXTREMELY REPETITIVE STRUCTURE, The Journal of biological chemistry, 271(31), 1996, pp. 18892-18897
The group B Streptococcus (GBS) causes the majority of life threatenin
g bacterial infections in newborn children. Most GBS strains isolated
from such infections express a surface protein, designated Rib, that c
onfers protective immunity and therefore is of interest for analysis o
f 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 seq
uence 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 com
mon among GBS strains lacking Rib, However, highly purified preparatio
ns of Rib and alpha did not crossreact immunologically, although the t
wo proteins show extensive amino acid residue identity (47% in the rep
eat region). When analyzed in Western blots, Rib and alpha give rise t
o a regularly spaced ladder pattern, apparently due to hydrolysis of a
cid-labile Asp Pro bonds in the repeats. We conclude that Rib and alph
a are members of a novel family of streptococcal surface proteins with
unusual repetitive structure.