Abstract
Cell wall glycopolymers on the surface of Gram-positive bacteria are fundamental to bacterial physiology and infection biology. Here we identify gacH, a gene in the S. pyogenes Group A Carbohydrate (GAC) biosynthetic cluster, in two independent transposon library screens for its ability to confer resistance to zinc and susceptibility to the bactericidal enzyme human group IIA secreted phospholipase A2. Subsequent structural and phylogenetic analysis of the GacH extracellular domain revealed that GacH represents a new class of glycerol phosphate (GroP) transferase. We detected the presence of GroP in the GAC as well as the Serotype c Carbohydrate (SCC) from S. mutans, which depended on the presence of the respective gacH homologs. Finally, NMR analysis of GAC confirmed that GroP is attached to approximately 30% of the GAC N-acetylglucosamine side-chains at the C6 hydroxyl group. This previously unrecognized structural modification impacts host-pathogen interaction and has implications for vaccine design.
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