Centrins in retinal photoreceptor cells: regulators in the connecting cilium.
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.
Trojan
Philipp
P
Institut für Zoologie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany.
Krauss
Norbert
N
Choe
Hui-Woog
HW
Giessl
Andreas
A
Pulvermüller
Alexander
A
Wolfrum
Uwe
U
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*
D002135:Calcium-Binding Proteins; D002868:Chromosomal Proteins, Non-Histone; D003285:Contractile Proteins; D005136:Eye Proteins; C056608:caltractin; D002118:Calcium