Activated FV (FVa) is a key coagulation cofactor that accelerates the production of thrombin. Multimerin-1 (MMRN1) binds to FV and plays a role in the storage and stabilization of factor V in platelets [, ]. It is a ligand for integrin alpha-IIb/beta-3 and integrin alpha-V/beta-3 on activated platelets, and may function as an extracellular matrix or adhesive protein [].