Coupling of photoexcited rhodopsin to inositol phospholipid hydrolysis in fly photoreceptors.

Abstract

ABSTRACTformed is inositol trisphosphate, and that this product is rapidly hydrolyzed by a specific phosphomonoesterase. Introduction of inositol trisphosphate to the intact photoreceptor cell mimics the effect of light, and bisphosphoglycerate, which inhibits inositol trisphosphate hydrolysis, enhances the effects of inositol trisphosphate and of dim light. The interaction of photoexcited rhodopsin with a G protein is thus similar in both vertebrate and invertebrate photoreceptors. These G proteins, however, activate different photoreceptor enzymes: phospholipase C in invertebrates and cGMP phosphodiesterase in vertebrates.

Translocation of Gqα Mediates Long-Term Adaptation inDrosophilaPhotoreceptors

“…This property allows measuring of the physiological implication of G q ␣ movements in vivo at the highest resolution. Photon absorption by rhodopsin in fly photoreceptors activates either one (Scott et al, 1995) or few G q ␣ protein molecules (Minke and Stephenson, 1985;Hardie et al, 2002), which subsequently activates PLC (Devary et al, 1987;Bloomquist et al, 1988) and leads, in a still unclear way, to the generation of a single-photon response called a quantum bump (Yeandle and Spiegler, 1973). The bumps sum to produce the macroscopic response to light (Dodge et al, 1968;Barash and Minke, 1994).…”

Cloning of a Drosophila melanogaster guanine nucleotide regulatory protein beta-subunit gene and characterization of its expression during development.

“…5 (18), and GTP analogs induce membrane depolarization in Musca photoreceptors (17). Lightdependent GTP binding and increased inositolphospholipid turnover are exhibited by fly (Musca and Drosophila) eye membranes (36). Pertussis toxin modifies specific substrates with properties similar to G-protein a subunits in octopus (21), and light stimulates inositolphospholipid turnover in octopus (37), Limulus (20), and squid (38).…”

“…The best characterized members of this family include transducin, which couples rhodopsin to a cyclic-GMP phosphodiesterase in vertebrate retinas (2), and Gs and G0, which function in the hormonally regulated stimulation aqd inhibition, respectively, of adenylate cyclase (1). G proteins are heterotrimers comprised of a (39-52 kDa), p (35)(36), and y (8-10 kDa) subunits. Members of this family share functional, structural, and common antigenic features.…”

Phototransduction in Drosophila

“…In vertebrates, the downstream effector for the G protein is a phosphodiesterase, which hydrolyzes 3′-5′ cyclic guanosine monophosphate (cGMP) to 5′ GMP, and leads to the closure of cGMP-gated ion channels to terminate the Na + and Ca 2+ influx [46,47]. In contrast, the effector for the drosophila heterotrimeric G protein is PLC, which catalyzes phosphatidylinositol-4,5-bisphosphate (PIP 2 ) to form inositol-1,3,5-trisphosphate (IP 3 ) and diacylglycerol (DAG) [3, [48][49][50]. Activation of PLC results in the opening of cation influx channels and leads to Na + and Ca 2+ influx [2,6].…”