Oglycosyl

Oglycosyl, commonly referred to as O-linked glycosylation, is a class of post-translational modifications in which sugar moieties are covalently attached to the oxygen atom of serine or threonine residues in proteins. The term encompasses several distinct pathways, including mucin-type O-GalNAc glycosylation, O-mannosylation, O-glucosylation, O-fucosylation, and O-GlcNAc, the latter primarily occurring in the nucleus and cytoplasm.

Mucin-type O-GalNAc glycosylation is initiated in the Golgi by a family of GalNAc-transferases (GalNAc-Ts), which transfer N-acetylgalactosamine to serine or threonine. This core can be extended by additional glycosyltransferases, producing diverse O-glycans that are elaborated into complex structures. O-glycosylation of secreted and membrane proteins contributes to protein stability, cell adhesion, and signaling, and dysregulation is linked to developmental disorders and cancer.

O-mannosylation attaches mannose to Ser/Thr residues and is essential for proper folding and function of several proteins, notably alpha-dystroglycan. O-glucosylation modifies epidermal growth factor-like repeats in Notch receptors and other proteins, influencing Notch signaling and development.

O-GlcNAc is a dynamic modification added by O-GlcNAc transferase (OGT) and removed by O-GlcNAcase (OGA). It occurs mainly on intracellular proteins and responds to cellular metabolic state, influencing protein stability, interactions, and transcription.

Detection and study rely on mass spectrometry, specialized antibodies, and lectins. O-glycosylation is implicated in development, immunity, cancer, and congenital disorders of glycosylation. Mapping site-specific O-glycosylation remains technically challenging due to heterogeneity of glycan structures.