Oligosaccharide configuration of fibrinogen Kaiserslautern: electrospray ionisation analysis of intact gamma chains

Abstract

Electrospray ionisation mass spectrometry was used to probe the structure of the new N-linked oligosaccharide in fibrinogen Kaiserslautern (gamma 380 Lys-->Asn). The mass increase of 2177 Da in the new beta chain indicated the attachment of a fully sialylated biantennary oligosaccharide on the new Asn residue; the expected increase for this change being 2192 Da. Some 95% of the new oligosaccharide was in the disialylated state while only 5% of the endogenous gamma chain carbohydrate was disialylated in the control. Mass measurements of intact Kaiserslautern gamma chains after neuraminidase treatment of the native fibrinogen confirmed a total of three residues of sialic acid in the dominant isoform. Incubation with endoglycosidase F showed that the new oligosaccharide was more resistant to hydrolysis than the endogenous one. Recent X-ray analyses of covalently linked D domains show that position gamma 380 is distant from both the GPR binding pocket and the D-D interface. It appears that the polymerisation defect of this fibrinogen results from electrostatic repulsion between condensing protofibrils and that this is induced by the two new residues of sialic acid that are present on the new gamma chain.