title: Inositol-1,4,5-trisphosphate-binding proteins controlling the phototransduction cascade of invertebrate visual cells.
abstract: The main phototransduction cascade in invertebrate visual cells involves the turnover of phosphatidylinositol, an important biochemical mechanism common to many signal-transduction systems. Light-activated rhodopsin stimulates guanine nucleotide exchange on the Gq class of G-protein, which activates phospholipase C to hydrolyze phosphatidylinositol 4,5-bisphosphate to inositol-1,4,5-trisphosphate and diacylglycerol. Subsequently, inositol-1,4,5-trisphosphate-binding proteins continue the signal cascade. Here, we report on the first inositol-1,4,5-trisphosphate-binding proteins demonstrated in an invertebrate visual system with our investigation of the photosensitive rhabdoms of squid. We screened the ability of proteins to interact with inositol-1,4,5-trisphosphate by affinity column chromatography with an inositol-1,4,5-trisphosphate analogue. We detected an inositol-1,4,5-trisphosphate-binding affinity in phospholipase C, receptor kinase and five other proteins in the cytosolic fraction and, surprisingly, rhodopsin in the membrane fraction. A binding assay with (3)H-labelled inositol-1,4,5-trisphosphate demonstrated the inositol-1,4,5-trisphosphate affinity of each of the purified proteins. Since rhodopsin, receptor kinase and phospholipase C are involved upstream of phosphatidylinositol turnover in the signal cascade, our result suggests that phosphatidylinositol turnover is important in feedback pathways in the signalling system.
authors.affiliation: Institution of Chemical and Physical Research (RIKEN), Sendai 980-0845, Japan. squid@postman.riken.go.jp
authors.forename: A
authors.initials: A
authors.lastname: Kishigami
authors.forename: T
authors.initials: T
authors.lastname: Ogasawara
authors.forename: Y
authors.initials: Y
authors.lastname: Watanabe
authors.forename: M
authors.initials: M
authors.lastname: Hirata
authors.forename: T
authors.initials: T
authors.lastname: Maeda
authors.forename: F
authors.initials: F
authors.lastname: Hayashi
authors.forename: Y
authors.initials: Y
authors.lastname: Tsukahara
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D049832:Decapodiformes / Q000502:physiology*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D012243:Rhodopsin / Q000502:physiology; D014785:Vision, Ocular / Q000502:physiology
chemical_list: D015220:Calcium Channels; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D012243:Rhodopsin