Localization of an O-glycosylation site in the alpha-subunit of the human platelet integrin GPIIb/IIIa involved in Baka (HPA-3a) alloantigen expression.

Abstract

The human alloantigen system Baka/b is associated with a Ile843-->Ser replacement on platelet glycoprotein IIb, the alpha-subunit of the integrin receptor for fibrinogen (GPIIb/IIIa). Recent immunological studies indicate that sialylated oligosaccharide chain(s) are also implicated in expression of the Baka determinant. Here we show that the GPIIb fragment 704-856 contains the whole Baka epitope, and that chemical cleavage of a single O-linked oligosaccharide chain within this GPIIb domain correlates with the loss of its anti-Baka antibodies binding ability. Ser847 was identified as the O-glycosylation site. Therefore, our results show that the Ser847 modification is responsible for the expression of the GPIIb-specific Baka alloantigen, and provide thus a link between the molecular biology and the immunologic observations.