CORE SUGAR RESIDUES OF THE N-LINKED OLIGOSACCHARIDES OF RUSSELLS VIPER VENOM FACTOR X-ACTIVATOR MAINTAIN FUNCTIONALLY ACTIVE POLYPEPTIDE STRUCTURE

We previously showed that the factor X activator of Russell's viper ve nom (RVV-X) contains six N-linked oligosaccharide chains: four in the heavy chain and one in each of the two light chains [Gowda, D. C., Jac kson, C. M., Hensley, P., & Davidson, E. A. (1994) J. Biol. Chem. 269, 10644-10650).] In the present study, we have investigated the role of the carbohydrate moieties in the structure and functional activity of RVV-X. Sequential removal of sugar residues from the terminal ends by exoglycosidases, up to 50% of total carbohydrates, did not significan tly alter the activity of RVV-X, demonstrating that the peripheral car bohydrate moieties are not involved in interactions with factor X. How ever, removal of whole oligosaccharide chains by N-glycanase caused an almost total loss of the ability of RVV-X to activate factor X to fac tor X(a). In parallel with these observations, circular dichroism spec troscopy showed that complete deglycosylation, but not the removal of peripheral sugars, caused a significant change in the secondary struct ure. Together, these data demonstrate that the oligosaccharide chains are necessary for the functional activity, and that the trimannosylchi tobiose core residues are sufficient for the maintenance of the native polypeptide structure.