The Construction of a Molecular Model for the Ternary Protein Complex of Intrinsic Coagulation Pathway Factors Provides Novel Insights for the Pathogenesis of Cross-Reactive Material Positive Coagulation Factor Mutations.

The human coagulation pathway orchestrates a complex series of events vital for maintaining vascular integrity, in which the intrinsic pathway plays a pivotal role in amplifying and propagating the coagulation response. Dysregulation of this pathway can lead to various bleeding disorders and thrombotic complications, posing significant health risks. In this pathway, the activation of Factor (F) X zymogen is catalyzed by the FVIIIa-FIXa binary complex, but knowledge about this is still incomplete. Understanding the structural and functional intricacies of the FVIIIa-FIXa-FX (zymogen) complex is imperative for unraveling the molecular mechanisms underlying coagulation regulation and guiding the development of targeted therapeutic interventions. In this study, utilizing Alphafold-Multimer and molecular dynamics (MD) simulations, we provide insights into factor interactions within the ternary complex and propose novel functional mechanisms contributing to the functional defects inflicted by their cross-reactive material (CRM) positive mutations. The amino acid residue replacement impairs the coagulation function by interfering with structure elements, including the following: (1) a knot-like structure between Arg-562 of FVIIIa's 558-Loop (residue 555-571) and the 333-Loop of FIXa (residue 333-346) contributes to FVIIIa-FIXa binding; (2) the a2 region of FVIIIa (residue 716-740) opens the lid of active site (FIXa's 266-Loop, residue 256-270) and facilitates substrate binding; (3) the activation peptide (AP) of FX zymogen (residue 143-194) not only assists in the activation of itself but also adheres the interface of the three factors like a double-sided tape. Our work provides novel insights for the pathogenesis of a number of reported clinical CRM-positive mutations and may lay the groundwork for the structure-based development of therapeutic interventions.