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Structure of human factor VIIa and its implications for the triggering of blood coagulation.

ABSTRACT: Factor VIIa (EC 3.4.21.21) is a trypsin-like serine protease that plays a key role in the blood coagulation cascade. On injury, factor VIIa forms a complex with its allosteric regulator, tissue factor, and initiates blood clotting. Although the structure of the binary complex has already been determined [Banner, D. W., D'Arcy, A., Chène, C., Winkler, F. K., Guha, A., Konigsberg, W. H., Nemerson, Y. & Kirchhofer, D. (1996) Nature (London) 380, 41-46], the conformational effects of cofactor binding to factor VIIa are not known in detail because of a lack of structural information on free factor VIIa. Here we report the structure of gamma-carboxyglutamic acid-domainless human coagulation factor VIIa at a resolution of 2.8 A. The molecule adopts an extended conformation within the crystal similar to that previously observed for the full-length protein in complex with tissue factor. Detailed comparison of free and tissue factor-bound factor VIIa reveals several structural differences. The binding mode of the active-site inhibitor D-Phe-Phe-Arg methyl ketone differs in the two structures, suggesting a role for the cofactor in substrate recognition. More importantly, a surface-exposed alpha-helix in the protease domain (residues 307-312), which is located at the cofactor recognition site, is distorted in the free form of factor VIIa. This subtle structural difference sheds light on the mechanism of the dramatic tissue factor-induced enhancement of factor VIIa activity.

SUBMITTER: Pike AC

PROVIDER: S-EPMC17709 | biostudies-literature | 1999 Aug

REPOSITORIES: biostudies-literature

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Structure of human factor VIIa and its implications for the triggering of blood coagulation.

Pike A C AC Brzozowski A M AM Roberts S M SM Olsen O H OH Persson E E

Proceedings of the National Academy of Sciences of the United States of America 19990801 16

Factor VIIa (EC 3.4.21.21) is a trypsin-like serine protease that plays a key role in the blood coagulation cascade. On injury, factor VIIa forms a complex with its allosteric regulator, tissue factor, and initiates blood clotting. Although the structure of the binary complex has already been determined [Banner, D. W., D'Arcy, A., Chène, C., Winkler, F. K., Guha, A., Konigsberg, W. H., Nemerson, Y. & Kirchhofer, D. (1996) Nature (London) 380, 41-46], the conformational effects of cofactor bindin ...[more]

PMID: 10430872

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Project description:A critical step in injury-induced initiation of blood coagulation is the formation of the complex between the trypsin-like protease coagulation factor VIIa (FVIIa) and its cofactor tissue factor (TF), which converts FVIIa from an intrinsically poor enzyme to an active protease capable of activating zymogens of downstream coagulation proteases. Unlike its constitutively active ancestor trypsin, FVIIa is allosterically activated (by TF). Here, ensemble refinement of crystallographic structures, which uses multiple copies of the entire structure as a means of representing structural flexibility, is applied to explore the impacts of inhibitor binding to trypsin and FVIIa, as well as cofactor binding to FVIIa. To assess the conformational flexibility and its role in allosteric pathways in these proteases, main-chain hydrogen bond networks are analyzed by calculating the hydrogen-bond propensity. Mapping pairwise propensity differences between relevant structures shows that binding of the inhibitor benzamidine to trypsin has a minor influence on the protease flexibility. For FVIIa, in contrast, the protease domain is "locked" into the catalytically competent trypsin-like configuration upon benzamidine binding as indicated by the stabilization of key structural features: the nonprime binding cleft and the oxyanion hole are stabilized, and the effect propagates from the active site region to the calcium-binding site and to the vicinity of the disulphide bridge connecting with the light chain. TF binding to FVIIa furthermore results in stabilization of the 170 loop, which in turn propagates an allosteric signal from the TF-binding region to the active site. Analyses of disulphide bridge energy and flexibility reflect the striking stability difference between the unregulated enzyme and the allosterically activated form after inhibitor or cofactor binding. The ensemble refinement analyses show directly, for the first time to our knowledge, whole-domain structural footprints of TF-induced allosteric networks present in x-ray crystallographic structures of FVIIa, which previously only have been hypothesized or indirectly inferred.

Dataset Information

Structure of human factor VIIa and its implications for the triggering of blood coagulation.

Publications

Structure of human factor VIIa and its implications for the triggering of blood coagulation.

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