Centrins, Potential Regulators of Transducin Translocation in

Changes in the intracellular Ca2+-concentration regulate the visual signal transduction cascade directly or more often indirectly through Ca2+-binding proteins. In this review, we discuss our recent findings on centrins in photoreceptor cells of the mammalian retina. Centrins are members of a highly conserved subgroup of the EF-hand superfamily of Ca2+-binding proteins commonly associated with centrosome-related structures. In photoreceptor cells, centrins are additionally prominent components in the connecting cilium linking the light sensitive outer segment compartment with the biosynthetically active inner segment. Our recent data indicate that Ca2+-activated centrin isoforms generate complexes with the visual heterotrimeric G-protein transducin by binding to its β-subunit. These Ca2+-dependent assemblies of centrin/G-protein complexes are novel aspects of translocation regulations of signaling proteins in sensory cells, and a potential link between molecular trafficking and signal transduction in general. 1