Structural and Functional Analysis of Cell Wall-Anchored PolypeptideAdhesin BspA in Streptococcus agalactiae

Streptococcus agalactiae (Group B Streptococcus, GBS) is the predominant cause of early-onset infectious disease in neonates and is responsible for life threatening infections in elderly and immune-compromised individuals. Clinical manifestations of GBS infection include sepsis, pneumonia and meningitis. Here we describe BspA, a deviant antigen I/II family polypeptide that confers adhesive properties linked to pathogenesis in GBS. Heterologous expression of BspA on the surface of the non-adherent bacterium Lactococcus lactis confers adherence to scavenger receptor gp340, human vaginal epithelium, and to the fungus Candida albicans. Complementary crystallographic and biophysical characterization of BspA reveal a novel β-sandwich adhesion domain and unique asparagine-dependent super-helical stalk. Collectively these findings establish a new bacterial adhesin structure that has in effect been hijacked by a pathogenic Streptococcus species to provide competitive advantage in human mucosal infections.