A. Pisano et al., GLYCOSYLATION SITES IDENTIFIED BY SOLID-PHASE EDMAN DEGRADATION - O-LINKED GLYCOSYLATION MOTIFS ON HUMAN GLYCOPHORIN-A, Glycobiology, 3(5), 1993, pp. 429-435
The human red blood cell sialoglycoprotein, glycophorin A (GpA), conta
ins a 'mucin-like' extensively O-glycosylated extracellular domain whi
ch carries the MN blood group antigens. We have revised the sites of O
-glycosylation in the extracellular domain of GpA by automated solid-p
hase Edman degradation, which allowed positive identification and quan
titation of O-glycosylated Ser and Thr residues, as well as the single
N-glycosylation site. One N-linked and 16 O-linked sites were identif
ied. Carbohydrate was absent on Ser1, Ser14, Ser15, Ser23, Thr28 and T
hr58 in GpA. We propose that the glycosyltransferases present in eryth
rocytes recognize specific flanking sequences around potential O-glyco
sylation sites. All 16 O-glycosylation sites are explained on the basi
s 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 Ly
s. The fourth motif is associated with Ser-glycosylation: Ser-Xaa-Xaa-
Xaa where at least one Xaa = Ser. These simple rules explain the glyco
sylation (or lack of it) on 21 of 22 Ser/Thr in the extracellular doma
in of GpA.