Copine I, also known as CPN1, is a member of the copine family. Copine I is a calcium-dependent membrane-binding protein which has a wide tissue distribution. Calcium-dependent membrane-binding proteins may regulate molecular events at the interface of the cell membrane and cytoplasm. Copine I contains two N-terminal type II C2 domains and an integrin A domain-like sequence in the C-terminus, while it does not contain a predicted signal sequence or transmembrane domains. Copine I may function in membrane trafficking.