Figure 6.

Schematic model showing functional role of Ca²⁺-induced dimerization of recoverin. A side-view of recoverin on the disk membrane is shown in the upper panel and a top-view of dimeric recoverin is shown in the lower panel. Myristoylation (red) targets Ca²⁺-bound recoverin to the membrane surface (upper panel). The Ca²⁺-bound recoverin dimer binds to the N-terminal helix of rhodopsin kinase (magenta), forming a 2:2 complex on the membrane surface that blocks phosphorylation of dimeric rhodopsin (lower panel). Intermolecular DEER distances for the recoverin dimer are indicated by double-headed arrows. Light activation leads to a lowering of cytosolic Ca²⁺, causing conformational changes in recoverin that promote dimer dissociation, sequester the covalently attached myristoyl group, and disrupt binding to rhodopsin kinase (RK). Ca²⁺-free monomeric recoverin then dissociates from the membrane surface, allowing RK to phosphorylate the C-terminal tail of light-excited rhodopsin (R*).