Centrins, gatekeepers for the light-dependent translocation of transducin through the photoreceptor cell connecting cilium.

Centrins are members of a highly conserved subgroup of the EF-hand superfamily of Ca 2+ -binding proteins commonly associated with centrosome-related structures. In the retina, centrins are also prominent components of the photoreceptor cell ciliary apparatus. Centrin isoforms are diVerentially localized at the basal body and in the lumen of the connecting cilium. All molecular exchanges between the inner and outer segments occur through this narrow connecting cilium. Ca 2+ -activated centrin isoforms bind to the visual heterotrimeric G-protein transducin via an interaction with the -subunit. Ca 2+ -dependent assemblies of centrin/G-protein complexes may regulate the transducin