The IgA‐binding β antigen of the c protein complex of Group B streptococci: sequence determination of its gene and detection of two binding regions

Abstract

The beta antigen of the lbc protein complex of Group B streptococci is a cell-surface receptor which binds the Fc region of human immunoglobulin A (IgA). Determination of the nucleotide sequence of the beta antigen gene shows that it encodes a preprotein having a molecular weight of 130,963 daltons and a polypeptide of 1164 amino acid residues that is typical of other Gram-positive cell-wall proteins. There is a long signal sequence of 37 amino acids at the N-terminus. Four of the five C-terminal amino acid residues are basic and are preceded by a hydrophobic stretch that appears to anchor the C-terminus in the cell membrane. To the N-terminal side of this hydrophobic stretch is a putative cell-wall-spanning region containing proline-rich repeated sequences. An unusual feature of these repeated sequences is a three-residue periodicity, whereby every first residue is a proline, the second residue is alternating positively or negatively charged, and the third residue is uncharged. The IgA-binding activity was approximately localized by expressing subfragments of the beta antigen as fusion proteins. Two distinct but adjacent DNA segments specified peptides that bound IgA, which indicates that the IgA-binding activity is located in two distinct regions of the protein.

SpsA, a novel pneumococcal surface protein with specific binding to secretory Immunoglobulin A and secretory component

“…At the N-terminal end of the protein, there is a potential signal-peptidase cleavage site (von Heijne, 1986) at amino acid 37. The predicted signal sequence of SpsA shows features common to other leader sequences of Gram-positive bacteria and is, for example, highly homologous to the signal sequence of ␤-antigen of c-protein of group B streptococci (Jerlströ m et al, 1991). Comparison of the signal sequences revealed an identity of 75% and 92% similarity, when conservative amino acid substitutions are taken into account.…”

“…The N-terminal part of SpsA with the SC-binding domain exhibits no homology either to pneumococcal IgA1-protease (Poulsen et al, 1996) or to other pneumococcal proteins (Paton et al, 1993). It also showed no homology to IgA-binding proteins from other bacterial species (Lindahl and Ä kerströ m, 1989;Jerlströ m et al, 1991). The purified SIgA-binding domain (amino acids 38-324) could, in low concentrations, completely inhibit competitively the binding of SIgA to pneumococci.…”

Members of the immunoglobulin superfamily in bacteria

“…agalactiae is an important human pathogen. S. agalactiae is a B group Streptococcus that causes meningitis in newborns (Jerlstrom et al, 1991). The IgA Fc receptor is part of the c complex that may contribute to the virulence of this organism (Lancefield et al, 1975).…”

“…The IgA Fc receptor is part of the c complex that may contribute to the virulence of this organism (Lancefield et al, 1975). Two specific IgA-binding regions have been defined; the second of these two regions contains the Ig-like domain (Jerlstrom et al, 1991). It is noteworthy that the human IgA Fc receptor contains two immunoglobulin-like domains.…”

Host–pathogen interactions in Streptococcus pyogenes infections, with special reference to puerperal fever and a comment on vaccine development

“…The non-repeated N-terminal region of R28 includes a region (shaded), which does not fit into the alignment with Rib. This region can be divided into two subregions, one with homology to the repeat region of the GBS α protein, which belongs to the same family as Rib and R28 [24], and one with homology to the GBS β protein, which is unrelated to the Rib and α proteins [45,46]. Thus, the R28 protein can be viewed as a chimera derived from three different GBS proteins [24].…”