title: Centrins in retinal photoreceptor cells: regulators in the connecting cilium.
abstract: Changes in the intracellular Ca2+ concentration regulate the visual signal transduction cascade directly or more often indirectly through Ca2+-binding proteins. Here we focus on centrins, which are members of a highly conserved subgroup of the EF-hand superfamily of Ca2+-binding proteins in photoreceptor cells of the vertebrate retina. Centrins are commonly associated with centrosome-related structures. In mammalian retinal photoreceptor cells, four centrin isoforms are expressed as prominent components in the connecting cilium linking the light-sensitive outer segment compartment with the metabolically active inner segment compartment. Our data indicate that Ca2+-activated centrin isoforms assemble into protein complexes with the visual heterotrimeric G-protein transducin. This interaction of centrins with transducin is mediated by binding to the betagamma-dimer of the heterotrimeric G-protein. More recent findings show that these interactions of centrins with transducin are reciprocally regulated via site-specific phosphorylations mediated by the protein kinase CK2. The assembly of centrin/G-protein complexes is a novel aspect of translocation regulation of signalling proteins in sensory cells, and represents a potential link between molecular trafficking and signal transduction in general.
authors.affiliation: Institut für Zoologie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Trojan
authors.forename: Norbert
authors.initials: N
authors.lastname: Krauss
authors.forename: Hui-Woog
authors.initials: HW
authors.lastname: Choe
authors.forename: Andreas
authors.initials: A
authors.lastname: Giessl
authors.forename: Alexander
authors.initials: A
authors.lastname: Pulvermüller
authors.forename: Uwe
authors.initials: U
authors.lastname: Wolfrum
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002868:Chromosomal Proteins, Non-Histone / Q000502:physiology*; D002923:Cilia / Q000378:metabolism*; D003285:Contractile Proteins / Q000502:physiology*; D005136:Eye Proteins / Q000502:physiology*; D006801:Humans; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D014785:Vision, Ocular / Q000502:physiology*
chemical_list: D002135:Calcium-Binding Proteins; D002868:Chromosomal Proteins, Non-Histone; D003285:Contractile Proteins; D005136:Eye Proteins; C056608:caltractin; D002118:Calcium