protein kinase C conserved region 1 (C1 domain) superfamilyThe C1 domain is a cysteine-rich zinc binding domain that does not bind DNA nor possess structural similarity to conventional zinc finger domains. It contains the motif HX12CX2CXnCX2CX4HX2CX7C, where C and H are cysteine and histidine, respectively; X represents other residues; and n is either 13 or 14. C1 has a globular fold with two separate Zn(2+)-binding sites. It was originally discovered as lipid-binding modules in protein kinase C (PKC) isoforms. C1 domains that bind and respond to phorbol esters (PE) and diacylglycerol (DAG) are referred to as typical, and those that do not respond to PE and DAG are deemed atypical. A C1 domain may also be referred to as PKC or non-PKC C1, based on the parent protein's activity. Most C1 domain-containing non-PKC proteins act as lipid kinases and scaffolds, except PKD which acts as a protein kinase. PKC C1 domains play roles in membrane translocation and activation of the enzyme.