Regulation of the catalytic function of coagulation factor VIIa by a conformational linkage of surface residue Glu 154 to the active site

Coagulation factor VIIa is an allosterically regulated trypsin-like serine protease that initiates the coagulation pathways upon complex formation wit h its cellular receptor and cofactor tissue factor (TF). The analysis of a conformation-sensitive monoclonal antibody directed to the macromolecular s ubstrate exosite in the VIIa protease domain demonstrated a conformational link from this exosite to the catalytic cleft that is independent of cofact or-induced allosteric changes. In this study, we identify Glu 154 as a crit ical surface-exposed exosite residue side chain that undergoes conformation al changes upon active site inhibitor binding. The Glu 154 side chain is im portant for hydrolysis of scissile bond mimicking peptidyl p-nitroanilide s ubstrates, and for inhibition of VIIa's amidolytic function upon antibody b inding. This exosite residue is not Linked to the catalytic cleft residue L ys 192 which plays an important role in thrombin's allosteric coupling to e xosite I. Allosteric linkages between VIIa's active site and the cofactor b inding site or between the cofactor binding site and the macromolecular sub strate exosite were not influenced by mutation of Glu 154. Glu 154 thus onl y influences the linkage of the macromolecular substrate binding exosite to the catalytic center. These data provide novel evidence that allosteric re gulation of VIIa's catalytic function involves discrete and independent con formational linkages and that allosteric transitions in the VIIa protease d omain are not globally coupled.