One of the Ca2+ binding sites of recoverin exclusively controls interaction with rhodopsin kinase

Recoverin is a neuronal calcium sensor protein that controls the activity of rhodopsin kinase in a Ca2+-dependent manner. Mutations in the EF-hand Ca2+ binding sites are valuable tools for investigating the functional properties of recoverin. In the recoverin mutant E121Q (ReCE121Q) the high-affinity Ca2+ binding site is disabled. The non-myristoylated form of ReCE121Q binds one Ca2+ via its second Ca2+ -binding site (EF-hand 2), whereas the myristoylated variant does not bind Ca2+ at all. Binding of Ca2+ to non-myristoylated ReCE121Q apparently triggers exposure of apolar side chains, allowing for association with hydrophobic matrices. Likewise, an interaction surface for the recoverin target rhodopsin kinase is constituted upon Ca2+ binding to the non-acylated mutant. Structural changes resulting from Ca2+-occupation of EF-hand 2 in myristoylated and non-myristoylated recoverin variants are discussed in terms of critical conditions required for biological activity.