Glycosylation of serine/threonine-rich intrinsically disordered regions of membrane-associated proteins in streptococci

Proteins intrinsically disordered regions (IDR) lacking secondary or tertiary structure are present across all three domains of life. In prokaryotes these regions are understudied. Our genome-wide analysis revealed presence of Serine and Threonine-rich IDRs is several membrane-associated proteins in streptococci. We showed that in Streptococcus mutans IDRs are glycosylated with N-acetylglucosamine by PgfS. Lack of glycosylation resulted in defect in protein-based biofilm formation under stress. We connected this phenotype to degradation of post-translational chaperon PrsA. We discovered that O-linked glycosylation protects C-terminal Ser Thr-rich IDR of PrsA from proteolytic degradation and is critical for the biological function of PrsA in biofilm formation.