N-Acetylglucosaminylation of Serine-Aspartate repeat Proteins Promotes Staphylococcus aureus Bloodstream infection

Background: Staphylococcus aureus agglutinates in plasma in a manner that requires host fibrinogen and clumping factor A, a bacterial surface protein with serine-Aspartate (SD) repeats. Results: SdgB modifies serine residues in SD repeats with GlcNAc, and this glycosylation contributes to the pathogenesis of sepsis. Conclusion: Glycosylation of SD repeats aids bacterial escape from host defenses. Significance: Interference with glycosylation may alter staphylococcal infections. Staphylococcus aureus secretes products that convert host fibrinogen to fibrin and promote its agglutination with fibrin fibrils, thereby shielding bacteria from immune defenses. The agglutination reaction involves ClfA (clumping factor A), a surface protein with serine-Aspartate (SD) repeats that captures fibrin fibrils and fibrinogen. Pathogenic staphylococci express several different SD proteins that are modified by two glycosyltransferases, SdgA and SdgB. Here, we characterized three genes of S. aureus, aggA, aggB (sdgA), and aggC (sdgB), and show that aggA and aggC contribute to staphylococcal agglutination with fibrin fibrils in human plasma. We demonstrate that aggB (sdgA) and aggC (sdgB) are involved in GlcNAc modification of the ClfA SD repeats. However, only sdgB is essential for GlcNAc modification, and an sdgB mutant is defective in the pathogenesis of sepsis in mice. Thus, GlcNAc modification of proteins promotes S. aureus replication in the bloodstream of mammalian hosts.