Browse
Submit Data
Databases
API
Help

Dataset Information

0 Views

0 Connections

0 Citations

0 Reanalyses

0 Downloads

Omics score: 0

Light-dependent GTP-binding proteins in squid photoreceptors.

ABSTRACT: Previous biochemical and electrophysiological evidence suggests that in invertebrate photoreceptors, a GTP-binding protein (G-protein) mediates the actions of photoactivated rhodopsin in the initial stages of transduction. We find that squid photoreceptors contain more than one protein (molecular masses 38, 42 and 46 kDa) whose ADP-ribosylation by bacterial exotoxins is light-sensitive. Several lines of evidence suggest that these proteins represent distinct alpha subunits of G-proteins. (1) Pertussis toxin and cholera toxin react with distinct subsets of these polypeptides. (2) Only the 42 kDa protein immunoreacts with the monoclonal antibody 4A, raised against the alpha subunit of the G-protein of vertebrate rods [Hamm & Bownds (1984) J. Gen. Physiol. 84. 265-280]. (3) In terms of ADP-ribosylation, the 42 kDa protein is the least labile to freezing. (4) Of the 38 kDa and 42 kDa proteins, the former is preferentially extracted with hypo-osmotic solutions, as demonstrated by the solubility of its ADP-ribosylated state and by the solubility of the light-dependent binding of guanosine 5'-[gamma-thio]triphosphate. The specific target enzymes for the observed G-proteins have not been established.

SUBMITTER: Robinson PR

PROVIDER: S-EPMC1149659 | biostudies-other | 1990 Nov

REPOSITORIES: biostudies-other

ACCESS DATA

Json Xml

Similar Datasets

Activation of the GTP-binding protein Gq by rhodopsin in squid photoreceptors.

Project description:Photoaffinity labelling by a GTP analogue has been used to identify a 42 kDa band as the major G alpha subunit in squid photoreceptor membranes, recently identified by partial sequence analysis to be a member of the Gq sub-group of GTP-binding proteins [Pottinger, Ryba, Keen & Findlay (1991) Biochem. J. 279, 323-326]. Guanine-nucleotide-binding displacement analysis gave a stoichiometry of 1 G-protein per 12.5 rhodopsin molecules, the same as in vertebrate rod photoreceptors. Binding was not detected above background in the dark, but was rapidly activated by light. Unlike vertebrate transducin, this G-protein is very temperature-sensitive. GTP binding is maximal at temperatures less than 10 degrees C and is much decreased after several minutes above 18 degrees C. The light-stimulated GTPase rate is maximal around 10 degrees C, above which the loss of binding sites counteracts the increase in hydrolytic rate per site. Earlier studies described light-sensitive G alpha components of 40 and 45 kDa, by ADP-ribosylation in the presence of cholera and pertussis toxins. These are now shown to be very minor components, as the prolonged treatment at elevated temperature required for ADP-ribosylation is sufficient to inactivate the major G alpha totally. Unlike the minor G alpha components, the 42 kDa G alpha is not inhibited by Ca2+.

| S-EPMC1133198 | biostudies-other

The identification and purification of the heterotrimeric GTP-binding protein from squid (Loligo forbesi) photoreceptors.

Project description:The principal GTP-binding protein (G-protein) from squid (Loligo forbesi) photoreceptor membranes has been identified by amino acid sequencing. The heterotrimeric protein was purified by detergent solubilization and ion-exchange chromatography. The amino acid sequence of the G-protein alpha-subunit (G-alpha) indicates that this subunit is closely related to the recently characterized Gq subgroup, whereas the G-gamma subunit varies widely in sequence from other homologues.

| S-EPMC1151585 | biostudies-other

Sequence of the beta-subunit of the phosphatidylinositol-specific phospholipase C-directed GTP-binding protein from squid (Loligo forbesi) photoreceptors.

Project description:The beta-subunit (G-beta) of the squid (Loligo forbesi) visual GTP-binding protein (G-protein), thought to be associated with a phosphatidylinositol-specific phospholipase C, has been identified and the sequence of the protein determined from its cDNA. The predicted polypeptide has a very marked sequence similarity with its mammalian counterparts (80-90% identity). Squid G-beta also has somewhat lower similarity to the yeast protein STE4 (approx. 40% identity). The role of G-beta in signal transduction is discussed in the light of its pronounced structural conservation.

| S-EPMC1149903 | biostudies-other

Nucleotide exchange-dependent and nucleotide exchange-independent functions of plant heterotrimeric GTP-binding proteins.

Project description:Heterotrimeric guanine nucleotide-binding proteins (G proteins), which are composed of ?, ?, and ? subunits, are versatile, guanine nucleotide-dependent, molecular on-off switches. In animals and fungi, the exchange of GDP for GTP on G? controls G protein activation and is crucial for normal cellular responses to diverse extracellular signals. The model plant Arabidopsis thaliana has a single canonical G? subunit, AtGPA1. We found that, in planta, the constitutively active, GTP-bound AtGPA1(Q222L) mutant and the nucleotide-free AtGPA1(S52C) mutant interacted with G??1 and G??2 dimers with similar affinities, suggesting that G protein heterotrimer formation occurred independently of nucleotide exchange. In contrast, AtGPA1(Q222L) had a greater affinity than that of AtGPA1(S52C) for G??3, suggesting that the GTP-bound conformation of AtGPA1(Q222L) is distinct and tightly associated with G??3. Functional analysis of transgenic lines expressing either AtGPA1(S52C) or AtGPA1(Q222L) in the gpa1-null mutant background revealed various mutant phenotypes that were complemented by either AtGPA1(S52C) or AtGPA1(Q222L). We conclude that, in addition to the canonical GDP-GTP exchange-dependent mechanism, plant G proteins can function independently of nucleotide exchange.

| S-EPMC6988777 | biostudies-literature

Septin6 and Septin7 GTP binding proteins regulate AP-3- and ESCRT-dependent multivesicular body biogenesis.

Project description:Septins (SEPTs) form a family of GTP-binding proteins implicated in cytoskeleton and membrane organization, cell division and host/pathogen interactions. The precise function of many family members remains elusive. We show that SEPT6 and SEPT7 complexes bound to F-actin regulate protein sorting during multivesicular body (MVB) biogenesis. These complexes bind AP-3, an adapter complex sorting cargos destined to remain in outer membranes of maturing endosomes, modulate AP-3 membrane interactions and the motility of AP-3-positive endosomes. These SEPT-AP interactions also influence the membrane interaction of ESCRT (endosomal-sorting complex required for transport)-I, which selects ubiquitinated cargos for degradation inside MVBs. Whereas our findings demonstrate that SEPT6 and SEPT7 function in the spatial, temporal organization of AP-3- and ESCRT-coated membrane domains, they uncover an unsuspected coordination of these sorting machineries during MVB biogenesis. This requires the E3 ubiquitin ligase LRSAM1, an AP-3 interactor regulating ESCRT-I sorting activity and whose mutations are linked with Charcot-Marie-Tooth neuropathies.

| S-EPMC4224394 | biostudies-literature

LRRK2 kinase activity is dependent on LRRK2 GTP binding capacity but independent of LRRK2 GTP binding.

Project description:Leucine rich repeat kinase 2 (LRRK2) is a Parkinson's disease (PD) gene that encodes a large multidomain protein including both a GTPase and a kinase domain. GTPases often regulate kinases within signal transduction cascades, where GTPases act as molecular switches cycling between a GTP bound "on" state and a GDP bound "off" state. It has been proposed that LRRK2 kinase activity may be increased upon GTP binding at the LRRK2 Ras of complex proteins (ROC) GTPase domain. Here we extensively test this hypothesis by measuring LRRK2 phosphorylation activity under influence of GDP, GTP or non-hydrolyzable GTP analogues GTPγS or GMPPCP. We show that autophosphorylation and lrrktide phosphorylation activity of recombinant LRRK2 protein is unaltered by guanine nucleotides, when co-incubated with LRRK2 during phosphorylation reactions. Also phosphorylation activity of LRRK2 is unchanged when the LRRK2 guanine nucleotide binding pocket is previously saturated with various nucleotides, in contrast to the greatly reduced activity measured for the guanine nucleotide binding site mutant T1348N. Interestingly, when nucleotides were incubated with cell lysates prior to purification of LRRK2, kinase activity was slightly enhanced by GTPγS or GMPPCP compared to GDP, pointing to an upstream guanine nucleotide binding protein that may activate LRRK2 in a GTP-dependent manner. Using metabolic labeling, we also found that cellular phosphorylation of LRRK2 was not significantly modulated by nucleotides, although labeling is significantly reduced by guanine nucleotide binding site mutants. We conclude that while kinase activity of LRRK2 requires an intact ROC-GTPase domain, it is independent of GDP or GTP binding to ROC.

| S-EPMC3155532 | biostudies-literature

Light-Photoreceptors and Proteins Related to <i>Monilinia laxa</i> Photoresponses.

Project description:Light represents a ubiquitous source of information for organisms to evaluate their environment. The influence of light on colony growth and conidiation was determined for three Monilinia laxa isolates. The highest mycelial growth rate was observed under red light for the three M. laxa isolates, followed by green light, daylight or darkness. However, reduced sporulation levels were observed in darkness and red light, but conidiation enhancement was found under daylight, black and green light with more hours of exposure to light. Putative photoreceptors for blue (white-collar and cryptochromes), green (opsins), and red light (phytochromes) were identified, and the photoresponse-related regulatory family of velvet proteins. A unique ortholog for each photoreceptor was found, and their respective domain architecture was highly conserved. Transcriptional analyses of uncovered sets of genes were performed under daylight or specific color light, and both in time course illumination, finding light-dependent triggered gene expression of MlVEL2, MlPHY2, MlOPS2, and MlCRY2, and color light as a positive inductor of MlVEL3, MlVEL4, MlPHY1, and MlCRY1 expression. M. laxa has a highly conserved set of photoreceptors with other light-responsive fungi. Our phenotypic analyses and the existence of this light-sensing machinery suggest transcriptional regulatory systems dedicated to modulating the development and dispersion of this pathogen.

| S-EPMC7827745 | biostudies-literature

GTP-binding proteins mediate transmitter inhibition of voltage-dependent calcium channels.

Project description:The modulation of voltage-dependent calcium channels by hormones and neurotransmitters has important implications for the control of many Ca2+-dependent cellular functions including exocytosis and contractility. We made use of electrophysiological techniques, including whole-cell patch-clamp recordings from dorsal root ganglion (DRG) neurones, to demonstrate a role for GTP-binding proteins (G-proteins) as signal transducers in the noradrenaline- and gamma-aminobutyric acid (GABA)-induced inhibition of voltage-dependent calcium channels. This action of the transmitters was blocked by: (1) preincubation of the cells with pertussis toxin (a bacterial exotoxin catalysing ADP-ribosylation of G-proteins); or (2) intracellular administration of guanosine 5'-O-(2-thiodiphosphate) (GDP-beta-S), a non-hydrolysable analogue of GDP that competitively inhibits the binding of GTP to G-proteins. Our findings provide the first direct demonstration of the G-protein-mediated inhibition of voltage-dependent calcium channels by neurotransmitters. This mode of transmitter action may explain the ability of noradrenaline and GABA to presynaptically inhibit Ca2+-dependent neurosecretion from DRG sensory neurones.

| S-EPMC2926796 | biostudies-other

Targeted Quantitative Profiling of GTP-Binding Proteins in Cancer Cells Using Isotope-Coded GTP Probes.

Project description:GTP-binding proteins play important roles in many essential biological processes, including cell signaling, trafficking, and protein synthesis. To assess quantitatively these proteins at the whole proteome level, we developed a high-throughput targeted proteomic method based on the use of isotope-coded GTP probes and multiple-reaction monitoring (MRM) analysis. Targeted proteins were labeled with desthiobiotin-GTP probes, digested with trypsin, and the ensuing desthiobiotin-conjugated peptides were enriched with streptavidin beads for LC-MS/MS analysis. We also established a Skyline MRM library based on shotgun proteomic data acquired for 12 different human cell lines. The library contained 605 tryptic peptides derived from 217 GTP-binding proteins, representing approximately 60% of the annotated human GTP-binding proteome. By using this library, in conjunction with isotope-coded GTP probes and scheduled LC-MRM analysis, we investigated the differential expression of GTP-binding proteins in a pair of primary/metastatic colon cancer cell lines (SW480 and SW620). We were able to quantify 97 GTP-binding proteins, and we further validated the differential expression of several GTP-binding proteins by Western blot analysis. Together, we developed a facile targeted quantitative proteomic method for the high-throughput analysis of GTP-binding proteins and applied the method for probing the altered expression of these proteins involved in colon cancer metastasis.

| S-EPMC6434709 | biostudies-literature

Calcium activates the light-dependent conductance in melanopsin-expressing photoreceptors of amphioxus.

Project description:Melanopsin, the photopigment of the "circadian" receptors that regulate the biological clock and the pupillary reflex in mammals, is homologous to invertebrate rhodopsins. Evidence supporting the involvement of phosphoinositides in light-signaling has been garnered, but the downstream effectors that control the light-dependent conductance remain unknown. Microvillar photoreceptors of the primitive chordate amphioxus also express melanopsin and transduce light via phospholipase-C, apparently not acting through diacylglycerol. We therefore examined the role of calcium in activating the photoconductance, using simultaneous, high time-resolution measurements of membrane current and Ca(2+) fluorescence. The light-induced calcium rise precedes the onset of the photocurrent, making it a candidate in the activation chain. Moreover, photolysis of caged Ca elicits an inward current of similar size, time course and pharmacology as the physiological photoresponse, but with a much shorter latency. Internally released calcium thus emerges as a key messenger to trigger the opening of light-dependent channels in melanopsin-expressing microvillar photoreceptors of early chordates.

| S-EPMC4485138 | biostudies-literature

OmicsDI is part of the ELIXIR infrastructure

OmicsDI is an Elixir interoperability service. Learn more ›

Tweets

OmicsDI Databases

PRIDE
PeptideAtlas
MassIVE
JPOST Repository
Physiome Model Repository

EGA
EVA
ENA
LINCS
PAXDB
Cell Collective

MetaboLights
Metabolomics Workbench
MetabolomeExpress
GNPS
BioModels
FAIRDOMHub

ArrayExpress
dbGaP
ExpressionAtlas
GEO
NODE

Information

Databases
Help
API
Contact us
Code on GitHub
Terms of use
Submit Data