Crystal structure of active site inhibited coagulation factor VIIA in complex with soluble tissue factor
[FA7_HUMAN] Defects in F7 are the cause of factor VII deficiency (FA7D) [MIM:227500]. A hemorrhagic disease with variable presentation. The clinical picture can be very severe, with the early occurrence of intracerebral hemorrhages or repeated hemarthroses, or, in contrast, moderate with cutaneous-mucosal hemorrhages (epistaxis, menorrhagia) or hemorrhages provoked by a surgical intervention. Finally, numerous subjects are completely asymptomatic despite very low factor VII levels.                       
[FA7_HUMAN] Initiates the extrinsic pathway of blood coagulation. Serine protease that circulates in the blood in a zymogen form. Factor VII is converted to factor VIIa by factor Xa, factor XIIa, factor IXa, or thrombin by minor proteolysis. In the presence of tissue factor and calcium ions, factor VIIa then converts factor X to factor Xa by limited proteolysis. Factor VIIa will also convert factor IX to factor IXa in the presence of tissue factor and calcium. [TF_HUMAN] Initiates blood coagulation by forming a complex with circulating factor VII or VIIa. The [TF:VIIa] complex activates factors IX or X by specific limited protolysis. TF plays a role in normal hemostasis by initiating the cell-surface assembly and propagation of the coagulation protease cascade.
Publication Abstract from PubMed
The remarkably high specificity of the coagulation proteases towards macromolecular substrates is provided by numerous interactions involving the catalytic groove and remote exosites. For FVIIa [activated FVII (Factor VII)], the principal initiator of coagulation via the extrinsic pathway, several exosites have been identified, whereas only little is known about the specificity dictated by the active-site architecture. In the present study, we have profiled the primary P4-P1 substrate specificity of FVIIa using positional scanning substrate combinatorial libraries and evaluated the role of the selective active site in defining specificity. Being a trypsin-like serine protease, FVIIa had P1 specificity exclusively towards arginine and lysine residues. In the S2 pocket, threonine, leucine, phenylalanine and valine residues were the most preferred amino acids. Both S3 and S4 appeared to be rather promiscuous, however, with some preference for aromatic amino acids at both positions. Interestingly, a significant degree of interdependence between the S3 and S4 was observed and, as a consequence, the optimal substrate for FVIIa could not be derived directly from a subsite-directed specificity screen. To evaluate the role of the active-site residues in defining specificity, a series of mutants of FVIIa were prepared at position 239 (position 99 in chymotrypsin), which is considered to be one of the most important residues for determining P2 specificity of the trypsin family members. This was confirmed for FVIIa by marked changes in primary substrate specificity and decreased rates of antithrombin III inhibition. Interestingly, these changes do not necessarily coincide with an altered ability to activate Factor X, demonstrating that inhibitor and macromolecular substrate selectivity may be engineered separately.
Engineering the substrate and inhibitor specificities of human coagulation Factor VIIa.,Larsen KS, Ostergaard H, Bjelke JR, Olsen OH, Rasmussen HB, Christensen L, Kragelund BB, Stennicke HR Biochem J. 2007 Aug 1;405(3):429-38. PMID:17456045
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.