Autophosphorylation restrains the apoptotic activity of DRP‐1 kinase by controlling dimerization and calmodulin binding

DRP‐1 is a pro‐apoptotic Ca2+/calmodulin (CaM)‐regulated serine/threonine kinase, recently isolated as a novel member of the DAP‐kinase family of proteins. It contains a short extra‐catalytic tail required for homodimerization. Here we identify a novel regulatory mechanism that controls its pro‐apoptotic functions. It comprises a single autophosphorylation event mapped to Ser308 within the CaM regulatory domain. A negative charge at this site reduces both the binding to CaM and the formation of DRP‐1 homodimers. Conversely, the dephosphorylation of Ser308, which takes place in response to activated Fas or tumour necrosis factor‐α death receptors, increases the formation of DRP‐1 dimers, facilitates the binding to CaM and activates the pro‐apoptotic effects of the protein. Thus, the process of enzyme activation is controlled by two unlocking steps that must work in concert, i.e. dephosphorylation, which probably weakens the electrostatic interactions between the CaM regulatory domain and the catalytic cleft, and homodimerization. This mechanism of negative autophosphorylation provides a safety barrier that restrains the killing effects of DRP‐1, and a target for efficient activation of the kinase by various apoptotic stimuli.