Structure-activity studies on C-terminal hirudin peptides containing sulfated tyrosine residues

To clarify the role of the negative charge of the C-terminal region of hirudin, we chemically synthesized the C-terminal peptide of hirudin variant-1 (HV-1), HV-1-(54-65), and its analogs, [E61Y,E62Y]HV-1-(54-65) and [E62Y]HV-1-(54-65), and then sulfated the Tyr residue(s) in these peptides by both enzymic and chemical methods. Enzymic O-sulfation of Tyr residues in the peptides by use of sulfotransferase isolated from Eubacterium A-44 allowed us to produce four kinds of the sulfated peptide, whose C-terminal sequences were -PEY(SO3H)YLQ, -PYY(SO3H)YLQ, -PYYY(SO3H)LQ and -PYY(SO3H)Y(SO3H)LQ. On the other hand, all Tyr residues in the peptides were successfully sulfated by chemical reaction with N,N'-dicyclohexylcarbodiimide in the presence of sulfuric acid. Based on the analysis of structure-activity relationships of these sulfated peptides for thrombin inhibition, the Tyr62 and Tyr63 bisulfated peptide GDFEEIPEY(SO3H)Y(SO3H)LQ was found to be the most potent inhibitor of thrombin among the products tested. No increase in potency was observed by further substitution of Glu61 with Tyr(SO3H). The inhibitory activity by substitution with Tyr(SO3H) at position 63 was greater than that obtained by the substitution at position 62.