The influence of flanking sequences on O-glycosylation

The influence of flanking sequences on O-glycosylation of serine and threonine residues was explored by comparison of known acceptor sites. Positions -6, -1 and +3 relative to the site were identified as particularly significant. To test the hypothesis that O-glycosylation could be affected by amino acid sequence, a series of test peptides was made containing substitutions at the sensitive positions. In vitro glycosylation of the peptides confirmed that the acceptor status of threonine was markedly influenced by the residues present at positions -6, -1 and +3. Circular dichroism indicated that peptides which had random structure were glycosylated, except when they contained a charged residue at position -1.