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J Biol Chem. 2001 Jun 22;276(25):23105-8. Epub 2001 Apr 17.

Secondary substrate-binding exosite in the serine protease domain of activated protein C important for cleavage at Arg-506 but not at Arg-306 in factor Va.

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  • 1Department of Clinical Chemistry, Lund University, The Wallenberg Laboratory, MAS, SE-205 02 Malmö, Sweden.


Proteolytic inactivation of activated factor V (FVa) by activated protein C (APC) is a key reaction in the regulation of hemostasis. We now demonstrate the importance of a positive cluster in loop 37 of the serine protease (SP) domain of APC for the degradation of FVa. Lysine residues in APC at positions 37, 38, and 39 form a secondary binding site for FVa, which is important for cleavage of FVa at Arg-506 while having no effect on Arg-306 cleavage. In contrast, topological neighbors Lys-62, Lys-63, and Arg-74 in APC appear of minor importance in FVa degradation. This demonstrates that secondary binding exosites of APC specifically guide the proteolytic action of APC, resulting in a more favorable degradation of the 506-507 peptide bond as compared with the 306-307 bond.

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