Identification of an amino acid signature sequence predictive of protein G-inhibitable IgG3-binding activity in group-A streptococcal IgG-binding proteins.

Sequence comparison of six known group-A streptococcal IgG-binding proteins, sharing the common property of protein G-inhibitable IgG3-binding-activity, identified a highly conserved 35-amino-acid (aa) sequence (74-100% similarity) within an EQ-rich central conserved core region of each protein. A search of aa sequence databases identified four additional proteins with > 50% similarity to this consensus sequence. All of these proteins demonstrated protein G-inhibitable IgG3-binding activity. Taken together, these results identify a signature sequence that predicts the presence of a protein G-inhibitable IgG3-binding domain(s) in group-A streptococcal IgG-binding proteins.