Cryogenic electron microscopy and coagulation factors.

PURPOSE OF REVIEW: Cryogenic electron microscopy (cryo-EM) resolves the structures of proteins and their complexes under near-native conditions that are often inaccessible to other structural techniques. Cryo-EM has recently contributed significant advances in basic knowledge to the field of coagulation. New paradigms regarding individual domain role in protein-protein interactions have emerged, casting the main reactions of the coagulation cascade in a much-needed structural context. This review focuses on recent advances in the study of coagulation factors using cryo-EM.

RECENT FINDINGS: Cryo-EM structures have defined the architecture of Factor V/Va free and bound to their biological partners, revealing that protease domains dominate protein-protein interactions while auxiliary domains act as scaffolds. Breakthroughs in mapping autoantibody epitopes for prothrombin and Factor VIII have elucidated pathogenic mechanisms in antiphospholipid syndrome and hemophilia. Furthermore, cryo-EM is accelerating biotherapeutic design, evidenced by recent structures of Factor XIIa, prothrombin and engineered Factor VIII.

SUMMARY: Cryo-EM, often, enables the resolution of discrete macromolecular conformations using minimal quantities of full-length proteins. These structural insights enable the rational design of next-generation therapeutics and targeted diagnostics guided by near physiological forms, marking a new era in coagulation research. Future integration with HDX-MS, smFRET, and cryo-electron tomography (cryo-ET) will resolve these molecular machineries in situ on the surface of activated platelets and vascular beds.