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bioRxiv · 10.1101/219105

Structure and function of accessory Sec proteins involved in the adhesin export pathway of Streptococcus gordonii

Chen, Y.·Bensing, B. A.·Seepersaud, R.·Mi, W.·Liao, M.·Jeffrey, P. D.·Shajahan, A.·Sonon, R. N.·Azadi, P.·Sullam, P. M.·Rapoport, T. A.
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Abstract

Many pathogenic bacteria, including Streptococcus gordonii, possess a pathway for the export of a single serine-rich-repeat protein that mediates the adhesion of bacteria to host cells and the extracellular matrix. These adhesins are O-glycosylated by several cytosolic glycosyltransferases and require three accessory Sec proteins (Asp1-3) for export, but how the adhesins are processed for secretion is not well defined. Here, we show that O-glycosylation of S. gordonii adhesin GspB occurs in a sequential manner by three enzymes (GtfA/B, Nss, Gly) that attach N-acetylglucosamine and glucose to Ser/Thr residues. The modified substrate is subsequently transferred from the last glycosyltransferase to the Asp1/2/3 complex. Crystal structures show that both Asp1 and Asp3 are related to carbohydrate binding proteins. Asp1 also has an affinity for phospholipids, which is attenuated by Asp2. These results suggest a mechanism for the modification of adhesin in the cytosol and its subsequent targeting to the export machinery.

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Chen, Y., Bensing, B. A., Seepersaud, R., Mi, W., Liao, M., Jeffrey, P. D., Shajahan, A., Sonon, R. N., Azadi, P., Sullam, P. M., Rapoport, T. A.. 2017-11-14. Structure and function of accessory Sec proteins involved in the adhesin export pathway of Streptococcus gordonii. https://doi.org/10.1101/219105

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