Occurrence of O-linked Xyl-GlcNAc and Xyl-Glc disaccharides in trocarin, a factor Xa homolog from snake venom.

Trocarin is a 46515-Da group D prothrombin-activating glycoprotein from the venom of the Australian elapid, Tropidechis carinatus. Amino acid sequencing and functional characterization of trocarin demonstrated that it is a structural and functional homolog of mammalian blood coagulation factor (F)Xa. In this study we show that, in contrast to mammalian Xa, which is not glycosylated, trocarin contains an O-linked carbohydrate moiety in its light chain and an N-linked carbohydrate oligosaccharide in its heavy chain. Mass spectrometry and sugar compositional analysis indicate that the O-linked carbohydrate moiety is a mixture of Xyl-GlcNAc-, GlcNAc-, Xyl-Glc- and Glc- structures linked to Ser 52. The N-linked carbohydrate on Asn 45 of the heavy chain is a sialylated, diantennary oligosaccharide that is located at the lip of the active site of the prothrombin activator.