PGRMC2 (progesterone receptor membrane component 2), also known as DG6 (steroid receptor protein DG6) or PMBP (progesterone membrane-binding protein), is a single pass membrane protein belonging to the cytochrome b5 family (MAPR (membrane associated progesterone receptor) subfamily). Expressed in sperm, PGRMC2 is believed to function as a steroid receptor and may participate in the progesterone-dependent sperm acrosome reaction.