THE BINDING OF NATURAL VARIANTS OF HUMAN FACTOR-IX TO ENDOTHELIAL-CELLS

The Cia-domain of human factor IX contains a specific element required for the binding of factor IX to an endothelial cell surface protein. We have investigated the dependence of this interaction on the structu ral integrity of the adjacent hydrophobic stack and epidermal growth f actor-like domains. The ability of purified natural variants of human factor IX to compete with wild-type factor IX binding to the endotheli al cell surface was used to obtain apparent Ki values of the variants. Our data suggest that the functional integrity of the Gla domain, ena bling factor IX to specifically interact with an endothelial cell surf ace protein, depends on the structural and functional integrity of bot h the hydrophobic stack domain and the first epidermal growth factor-l ike domain.