The γ‐subunit of the principal G‐protein from squid (<i>Loligo forbesi</i>) photoreceptors contains a novel N‐terminal sequence

Visual transduction in the compound eye of flies is a well established model system for the study of G proteincoupled transduction pathways. To characterize key components of the phototransduction cascade we performed substractive hybridization screening. We cloned the cDNA coding for the visual G␥ (G␥ e ) subunit from Drosophila which had so far eluded identification at the molecular level. Northern blot analysis revealed the presence of a major, 1.4-kilobase(kb) G␥ e transcript and two minor transcripts of 1.8 and 6 kb in size. The major 1.4-kb mRNA is expressed preferentially in the eye. The spatial expression pattern determined for G␥ e as well as co-immunoprecipitation experiments demonstrated that G␥ e dimerizes with G␤ e to form the heterodimeric G␤␥ subunit which functions in visual transduction in the Drosophila compound eye. G␥ e shares common characteristics with the visual G␥ subunits of human rod and cone photoreceptors although different classes of G␣ subunits are employed in vertebrate and invertebrate phototransduction. By the molecular cloning and characterization of the visual ␥ subunit of Drosophila one of the few missing links in the well studied Drosophila phototransduction cascade has been characterized to complete our knowledge about the Drosophila visual transduction pathway.

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“…1B). An unusual stretch of highly charged amino acids located near the N terminus of visual G␥ from squid (33) has no parallel in DmG␥ e .…”

Section: Resultsmentioning

confidence: 99%

A Novel Gγ Isolated from Drosophila Constitutes a Visual G Protein γ Subunit of the Fly Compound Eye

Schulz

Huber

Schwab

et al. 1999

Journal of Biological Chemistry

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“…The retinal y I subunit is only 38% identical to brain y2 and equally different from the other mammalian ys. The @ subunit from squid is very similar to mammalian P I , but the y subunit from squid that was isolated in association with the @ subunit is so dissimilar from mammalian y that the relationship is only barely statistically significant compared to a random sequence (Lott et al, 1992). The existence of four different @ subunits and at least seven y subunits suggests that 28 different combinations are possible.…”

Section: Structure Of the By Subunitmentioning

confidence: 92%

G proteins: Critical control points for transmembrane signals

Neer

1994

Protein Science

121

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Heterotrimeric GTP-binding proteins (G proteins) that are made up of alpha and beta gamma subunits couple many kinds of cell-surface receptors to intracellular effector enzymes or ion channels. Every cell contains several types of receptors, G proteins, and effectors. The specificity with which G protein subunits interact with receptors and effectors defines the range of responses a cell is able to make to an external signal. Thus, the G proteins act as a critical control point that determines whether a signal spreads through several pathways or is focused to a single pathway. In this review, I will summarize some features of the structure and function of mammalian G protein subunits, discuss the role of both alpha and beta gamma subunits in regulation of effectors, the role of the beta gamma subunit in macromolecular assembly, and the mechanisms that might make some responses extremely specific and others rather diffuse.

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“…In addition, the PH domain of SQRK was flanked by two regions that share high sequence similarity to the squid G protein g subunit (Gg). Gg-like region 1, GLR-1, spanned amino acids 538-565 and GLR-2 spanned amino acids 631-683, and they showed 70% and 44% sequence similarity to the squid G protein g subunit, respectively (Lott et al, 1992).…”

Section: Amino Acid Sequence Domain Structure and Tissue Distributimentioning

confidence: 99%

cDNA cloning and characterization of a novel squid rhodopsin kinase encoding multiple modular domains

Mayeenuddin

Mitchell

2001

Vis Neurosci

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Rhodopsin phosphorylation is one of the key mechanisms of inactivation in vertebrate and invertebrate visual signal transduction. Here we report the cDNA cloning and protein characterization of a 70-kDa squid rhodopsin kinase, SQRK. The cDNA encoding the 70-kDa protein demonstrates high sequence identity with octopus rhodopsin kinase (92%) and mammalian β-adrenergic receptor kinases (63–65%), but only 33% similarity with bovine rhodopsin kinase, suggesting that invertebrate rhodopsin kinases may be structurally similar to β-adrenergic receptor kinases. This cDNA encodes three distinct modular domains: RGS, S/TKc, and PH domains. The native SQRK is an eye-specific protein that is only expressed in photoreceptor cells and the optic ganglion as determined by immunoblotting. Purified SQRK is able to phosphorylate both squid and bovine rhodopsin. Squid rhodopsin phosphorylation by purified SQRK was sensitive to both Mg2+ and GTPγS but was insensitive to Ca2+/CaM regulation. The ability of SQRK to phosphorylate rhodopsin was totally lost in the presence of SQRK-specific antibodies. Our results suggest that SQRK plays an important role in squid visual signal termination.

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The γ‐subunit of the principal G‐protein from squid (Loligo forbesi) photoreceptors contains a novel N‐terminal sequence

Cited by 15 publications

References 35 publications

A Novel Gγ Isolated from Drosophila Constitutes a Visual G Protein γ Subunit of the Fly Compound Eye

A Novel Gγ Isolated from Drosophila Constitutes a Visual G Protein γ Subunit of the Fly Compound Eye

G proteins: Critical control points for transmembrane signals

cDNA cloning and characterization of a novel squid rhodopsin kinase encoding multiple modular domains

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