Summary
Hemorrhagic factor V inhibitors frequently bind to the second C-type (C2) domain of
factor V and interfere with phospholipid binding. To define specific residues recognized
by inhibitors from four patients (one bovine thrombin-induced and three spontaneous
antibodies), epitope mapping was performed using recombinant human factor V lacking
most of the B-type domain (FV des B) and alanine-substituted mutants within the C2
domain (FV des B C2 mutants). FV des B C2 mutants located in the region between Lys2060 and Glu2069 were resistant to inhibition by three IgG preparations including the bovine thrombin-induced
antibody in both prothrombinase and phospholipid-binding assays. In contrast, mutations
at Lys2087 and Lys2092/ Glu2096 were significantly resistant to inhibition by the fourth IgG preparation in both
prothrombinase and phospholipid-binding assays. These results confirm interference
of phospholipid binding by hemorrhagic factor V inhibitors and support the role(s)
of these residues in phospholipid binding.
Presented in part at the 41st Annual Meeting of the American Society of Hematology,
New Orleans, Louisiana, December 3–7, 1999
Key words
Factor V - hemorrhagic inhibitor - epitope mapping - C2 domain - phospholipid binding