Copine 3 is a member of the copine family of evolutionarily conserved, soluble, calcium-dependent, membrane-binding proteins. Members of the copine family are involved in signal transduction and membrane trafficking. Copine 3 is ubiquitously expressed and contains two N-terminal C2 domains and one C-terminal VWFA (von Willebrand factor A) domain, which is also referred to as the A domain or the core domain. As is characteristic of the copine family, copine 3 functions in membrane trafficking and is capable of binding phospholipids in a calcium-dependent manner. Differing from other members of the copine family, copine 3 may possess some intrinsic kinase activity. Copine 3 exists as a monomer in the cytosol and undergoes a conformational change upon binding to calcium.