Crystal structure of active site-inhibited human coagulation factor VIIa (des-Gla)

Factor VIIa (FVIIa) is a crucial haemostatic protease consisting of four di stinct domains termed the Gla, epidermal growth factor-1 (EGF-1), EGF-2, an d protease domains (from N- to C-terminus). The crystal structure of human FVIIa inhibited at the active site with 1,5-dansyl-Glu-Gly-Arg-chloromethyl ketone and lacking the Gla domain has been solved to a resolution of 2.28 Angstrom. The EGF-2 and protease domains were well resolved, whereas no ele ctron density for the EGF-1 domain was observed, suggesting a flexible arra ngement or disorder within the crystal. Superposition of the protease domai n of the present structure with that previously resolved in the tissue fact or (TF)/FVIIai complex revealed that although overall the domain structures are similar, the EGF-2 domain is rotated by 7.5 degrees relative to the pr otease domain on binding TF.A single cleavage in the protease domain was fo und, between Arg315 and Lys316 (chymotrypsin numbering 170C-170D) in a FVII -specific insertion loop: this cleavage appeared to be essential for crysta llisation. Insertion of the heavy chain N-terminal Ile153 is essentially id entical in the two structures, as is the geometry of the active site residu es and the inhibitor C-terminal arginine residue. Some differences are seen in the cleaved loop, but changes in TF-contact residues are generally mino r. This structure supports the hypothesis that TF binding enables spatial d omain arrangements in the flexible FVIIa molecule necessary for procoagulan t function and furthermore that active site occupancy induces FVIIa active conformation via N-terminal insertion. (C) 1999 Academic Press.