Ca2+-myristoyl switch in the neuronal calcium sensor recoverin requires different functions of Ca2+-binding sites

Recoverin is an EF-hand Ca2+-binding protein that is suggested to control the activity of the G-protein-coupled receptor kinase GRK-1 or rhodopsin kinase in a Ca2+-dependent manner. It undergoes a Ca2+-myristoyl switch when Ca2+ binds to EF-hand 2 and 3. We investigated the mechanism of this switch by the use of point mutations in EF-hand 2 (E85Q) and 3 (E121Q) that impair their Ca2+ binding. EF-hand 2 and 3 display different properties and serve different functions. Binding of Ca2+ to recoverin is a sequential process, wherein EF-hand 3 is occupied first followed by the filling of EF-hand 2. After EF-hand 3 bound Ca2+, the subsequent filling of EF-hand 2 triggers the exposition of the myristoyl group and in turn binding of recoverin to membranes. In addition, EF-hand 2 controls the mean residence time of recoverin at membranes by decreasing the dissociation rate of recoverin from membranes by 10-fold. We discuss this mechanism as one critical step for inhibition of rhodopsin kinase by recoverin.