title: Large, identical, tandem repeating units in the C protein alpha antigen gene, bca, of group B streptococci.
abstract: Group B Streptococcus (GBS) is the leading cause of neonatal sepsis and meningitis in the United States. The surface-associated C protein alpha antigen of GBS is thought to have a role in both virulence and immunity. We previously cloned the C protein alpha antigen structural gene (named bca for group B, C protein, alpha) into Escherichia coli. Western blots of both the native alpha antigen and the cloned gene product demonstrate a regularly laddered pattern of heterogeneous polypeptides. The nucleotide sequence of the bca locus reveals an open reading frame of 3060 nucleotides encoding a precursor protein of 108,705 Da. Cleavage of a putative signal sequence of 41 amino acids yields a mature protein of 104,106 Da. The 20,417-Da N-terminal region of the alpha antigen shows no homology to previously described protein sequences and is followed by a series of nine tandem repeating units that make up 74% of the mature protein. Each repeating unit is identical and consists of 82 amino acids with a molecular mass of 8665 Da, which is encoded by 246 nucleotides. The size of the repeating units corresponds to the observed size differences in the heterogeneous ladder of alpha C proteins expressed by GBS. The C-terminal region of the alpha antigen contains a membrane anchor domain motif that is shared by a number of Gram-positive surface proteins. The large region of identical repeating units in bca defines protective epitopes and may play a role in generating phenotypic and genotypic diversity of the alpha antigen.
authors.affiliation: Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Boston, MA.
authors.forename: J L
authors.initials: JL
authors.lastname: Michel
authors.forename: L C
authors.initials: LC
authors.lastname: Madoff
authors.forename: K
authors.initials: K
authors.lastname: Olson
authors.forename: D E
authors.initials: DE
authors.lastname: Kling
authors.forename: D L
authors.initials: DL
authors.lastname: Kasper
authors.forename: F M
authors.initials: FM
authors.lastname: Ausubel
mesh_terms: D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal; D000954:Antigens, Surface / Q000032:analysis / Q000235:genetics*; D001426:Bacterial Proteins / Q000032:analysis / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D021382:Protein Sorting Signals / Q000235:genetics; D011994:Recombinant Proteins / Q000032:analysis; D012091:Repetitive Sequences, Nucleic Acid; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid; D013292:Streptococcus agalactiae / Q000235:genetics*; D016385:TATA Box
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; C077961:alpha C protein, group B streptococci