Calcium-dependent assembly of centrin-G-protein complex in photoreceptor cells

Photoexcitation of rhodopsin activates a heterotrimeric G-protein cascade leading to cyclic G MP 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 Ca2+-binding protein centrin 1 in a specific domain of this cilium. Coimmunoprecipitation, centrifugation, centrin overlay, size exclusion chromatography, and kinetic light-scattering experiments indicate that Ca2+-activated centrin 1 binds with high affinity and specificity to transducin. The assembly of centrin-G-protein complex is mediated by the betagamma-complex. The Ca2+-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.