Extensive Small-Angle X-ray Scattering Studies of Blood Coagulation Factor VIIa Reveal Interdomain Flexibility

摘要

Blood coagulation factor VIIa (FVIIa) is used in the treatment of replacement therapy resistantnhemophilia patients, and FVIIa is normally activated upon complex formation with tissue factor (TF), potentiallynin context with structural rearrangements. The solution behavior of uncomplexed FVIIa is important fornunderstanding the mechanism of activation and for the stability and activity of the pharmaceutical product.nHowever, crystal structures of FVIIa in complex with TF and of truncated free FVIIa reveal different overallnconformations while previous small-angle scattering studies suggest FVIIa always to be fully extended innsolution. Here, small-angle X-ray scattering analysis of multiple forms of FVIIa and TF under severalnexperimental conditions elaborate extensively on the understanding of the solution behavior of FVIIa.nWe reveal significant FVIIa domain flexibility in solution, whereas TF has a well-defined conforma-ntion. Unspecific formation of dimers of FVIIa is also observed and varies with experimental conditions.nIn particular, active site-inhibited FVIIa displays a distinct solution behavior different from that ofnuninhibited FVIIa, which may reflect structural rearrangements causing resistance to activation, therebynemphasizing the connection between the distribution of different conformations of FVII and thenmechanism of activation