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bioRxiv · 10.1101/2021.07.09.451823

SAXS analysis of the intrinsic tenase complex bound to lipid nanodisc highlights intermolecular contacts between factors VIIIa/IXa

Childers, K. C.·Peters, S. C.·Lollar, P.·Spencer, H. T.·Doering, C. B.·Spiegel, P. C.
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Abstract

The intrinsic tenase (Xase) complex, formed by factors (f)VIIIa and fIXa, forms on activated platelet surfaces and catalyzes the activation of factor X to Xa, stimulating thrombin production in the blood coagulation cascade. The structural organization of the membrane-bound Xase complex remains largely unknown, hindering our understanding of the structural underpinnings that guide Xase complex assembly. Here, we aimed to characterize the Xase complex bound to a lipid nanodisc with biolayer interferometry (BLI) and small angle X-ray scattering (SAXS). Using immobilized lipid nanodiscs, we measured binding rates and nanomolar affinities for fVIIIa, fIXa, and the Xase complex. An ab initio molecular envelope of the nanodisc-bound Xase complex allowed us to computationally model fVIIIa and fIXa docked onto a flexible lipid membrane and identify protein-protein interactions. Our results highlight multiple points of contact between fVIIIa and fIXa, including a novel interaction with fIXa at the fVIIIa A1-A3 domain interface. Lastly, we identified hemophilia A/B-related mutations with varying severities at the fVIIIa/fIXa interface that may regulate Xase complex assembly. Together, our results support the use of SAXS as an emergent tool to investigate the membrane-bound Xase complex and illustrate how mutations at the fVIIIa/fIXa dimer interface may disrupt or stabilize the activated enzyme complex.

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Childers, K. C., Peters, S. C., Lollar, P., Spencer, H. T., Doering, C. B., Spiegel, P. C.. 2021-07-10. SAXS analysis of the intrinsic tenase complex bound to lipid nanodisc highlights intermolecular contacts between factors VIIIa/IXa. https://doi.org/10.1101/2021.07.09.451823

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