Enrichment of protein annotations around O-glycosites. (A) Protein annotations from the UniprotKB database were used to determine whether specific protein features were enriched around (± 15 amino acids) O-glycosites relative to the background Ser/Thr distribution. Annotated features with a >1.2 fold-change and P < .01 (Fisher’s exact test, Bonferroni correction) are illustrated on the graph above. Note that O-glycosites often occurred in the vicinity of Ser/Thr phospho-sites and disulfide-bonded Cys, but at the expected frequency. Numbers above the bars indicate the count of O-glycosites found in the vicinity of the annotation. Fold-change indicates the under- or overenrichment of O-glycosites relative to the background frequency of Ser/Thr residues. Only annotations represented by >5 proteins and 10 glycosites were included in the analysis. (B) Graphic depiction showing examples of the different types of O-glycosylation identified in this study. rpt, repeat.