Coagulation factor XI/FXI His Tag Protein, Human

Coagulation factor XI (FXI) is a key serine protease zymogen in the blood coagulation cascade. Unlike other clotting factors, FXI circulates in plasma as a homodimer composed of two identical polypeptide chains linked by disulfide bonds. Structurally, FXI comprises four N-terminal Apple domains responsible for binding to other coagulation factors and platelets, and a C-terminal catalytic domain that, upon activation, exerts its proteolytic function.

Activation of FXI is primarily mediated by activated FXIIa or thrombin. Once activated, FXIa subsequently activates FIX, thereby linking the extrinsic pathway to the contact activation pathway, amplifying thrombin generation, and promoting thrombus formation and stabilization. Importantly, the function of FXI extends beyond hemostasis; it plays a significant role in maintaining vascular barrier function, activating platelets, mediating inflammatory responses, and regulating immunity. Loss-of-function mutations in the F11 gene lead to a mild bleeding disorder known as Rosenthal syndrome.