Structural Studies of Blood Coagulation Factor VIII in Protein Complexes

A deficiency in blood coagulation factor VIII (fVIII) is responsible for the inherited bleeding disorder hemophilia A, which affects approximately 1 in 5000 males. The development of inhibitory antibodies is a significant issue faced by hemophilia A patients receiving therapeutic infusions of fVIII. The C-terminal C2 domain of fVIII has been shown to be highly immunogenic and the site of binding for numerous antibodies of both the classical and non-classical classifications. A detailed understanding of the structural components involved in C2-antibody binding interactions is vital for the development of improved therapeutics for hemophilia patients. Here we present the structure of the classical antibody 3E6 bound to human C2 at 2.6 Å resolution. Previous studies have suggested that pairs of classical and non-classical antibodies may exhibit binding cooperativity. We hope to elucidate the molecular basis for this cooperativity through analysis of the structure of C2-3E6 and a previously determined ternary structure of C2 bound simultaneously to both 3E6 and the non-classical antibody G99. Furthermore, we are currently employing crystallographic techniques to study the interactions between FVIII and its circulatory partner von Willebrand factor (vWF), which is crucial for maintaining FVII levels in plasma. Two vWF domain mutants, TIL\u27E\u27 and D\u27D3, are being studied in complex with FVIII to elucidate detailed binding information