Title : Glycosylation
sites identified by solid-phase Edman degradation: O-linked glycosylation
motifs on human
glycophorin A
Abstract :
- The human red blood cell sialoglycoprotein , glycophorin A ( GpA ), contains a 'mucin-like' extensively O-glycosylated extracellular domain which carries the MN blood group antigens
- We have revised the sites of O-glycosylation in the extracellular domain of GpA by automated solid-phase Edman degradation, which allowed positive identification and quantitation of O-glycosylated Ser and Thr residues , as well as the single N-glycosylation site
- One N-linked and 16 O-linked sites were identified
- Carbohydrate was absent on Ser1, Ser14, Ser15, Ser23, Thr28 and Thr58 in GpA
- We propose that the glycosyltransferases present in erythrocytes recognize specific flanking sequences around potential O-glycosylation sites
- All 16 O-glycosylation sites are explained on the basis of four motifs
- Three motifs are associated with Thr-glycosylation: Xaa- Pro-Xaa-Xaa where at least one Xaa = Thr ; Thr-Xaa-Xaa-Xaa where at least one Xaa = Thr ; Xaa-Xaa- Thr-Xaa where at least one X = Arg or Lys
- The fourth motif is associated with Ser-glycosylation: Ser-Xaa-Xaa-Xaa where at least one Xaa = Ser
- These simple rules explain the glycosylation (or lack of it) on 21 of 22 Ser/Thr in the extracellular domain of GpA