Calcium-Dependent Assembly of Centrin-G-Protein Complex in Photoreceptor Cells

Photoexcitation of rhodopsin activates a heterotrimeric G-protein cascade leading to cyclic GMP hydrolysis in vertebrate photoreceptors. Light-induced exchanges of the visual G-protein transducin between the outer and inner segment of rod photoreceptors occur through the narrow connecting cilium. Here we demonstrate that transducin colocalizes with the Ca 2 -binding protein centrin 1 in a specific domain of this cilium. Coimmunoprecipitation, centrifugation, centrin overlay, size exclusion chromatography, and kinetic lightscattering experiments indicate that Ca 2 -activated centrin 1 binds with high affinity and specificity to transducin. The assembly of centrin‐G-protein complex is mediated by the -complex. The Ca 2 -dependent assembly of a G protein with centrin is a novel aspect of the supply of signaling proteins in sensory cells and a potential link between molecular translocations and signal transduction in general.