Novel staphylococcal glycosyltransferases SdgA and SdgB mediate immunogenicity and protection of virulence-associated cell wall proteins.

Wouter L W Hazenbos, Kimberly K Kajihara, Richard Vandlen, J Hiroshi Morisaki, Sophie M Lehar, Mark J Kwakkenbos, Tim Beaumont, Arjen Q Bakker, Qui Phung, Lee R Swem, Satish Ramakrishnan, Janice Kim, Min Xu, Ishita M Shah, Binh An Diep, Tao Sai, Andrew Sebrell, Yana Khalfin, Angela Oh, Chris Koth, S Jack Lin, Byoung-Chul Lee, Magnus Strandh, Klaus Koefoed, Peter S Andersen, Hergen Spits, Eric J Brown, Man-Wah Tan, Sanjeev Mariathasan

Index: PLoS Pathog. 9(10) , e1003653, (2013)

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Abstract

Infection of host tissues by Staphylococcus aureus and S. epidermidis requires an unusual family of staphylococcal adhesive proteins that contain long stretches of serine-aspartate dipeptide-repeats (SDR). The prototype member of this family is clumping factor A (ClfA), a key virulence factor that mediates adhesion to host tissues by binding to extracellular matrix proteins such as fibrinogen. However, the biological siginificance of the SDR-domain and its implication for pathogenesis remain poorly understood. Here, we identified two novel bacterial glycosyltransferases, SdgA and SdgB, which modify all SDR-proteins in these two bacterial species. Genetic and biochemical data demonstrated that these two glycosyltransferases directly bind and covalently link N-acetylglucosamine (GlcNAc) moieties to the SDR-domain in a step-wise manner, with SdgB appending the sugar residues proximal to the target Ser-Asp repeats, followed by additional modification by SdgA. GlcNAc-modification of SDR-proteins by SdgB creates an immunodominant epitope for highly opsonic human antibodies, which represent up to 1% of total human IgG. Deletion of these glycosyltransferases renders SDR-proteins vulnerable to proteolysis by human neutrophil-derived cathepsin G. Thus, SdgA and SdgB glycosylate staphylococcal SDR-proteins, which protects them against host proteolytic activity, and yet generates major eptopes for the human anti-staphylococcal antibody response, which may represent an ongoing competition between host and pathogen.