grk7b (GRK7-2) is one of two zebrafish paralogs of the cone-type G protein-coupled receptor kinase GRK7, an AGC-family serine/threonine kinase with an N-terminal RGS homology domain and a C-terminal geranylgeranylated cysteine that anchors it to photoreceptor membranes. Recombinant Grk7b phosphorylates light-activated rhodopsin (EC 2.7.11.14), the reaction that initiates opsin deactivation and arrestin binding during photoresponse shutoff and light adaptation. Its transcript is enriched in UV cones, and it is also expressed in the pineal organ and brain, whereas the paralog grk7a serves the other cone subtypes and is the kinase whose knockdown delays cone recovery and pineal parapinopsin inactivation; a distinct in vivo role for grk7b has not yet been demonstrated.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Cytoplasm (is_active_in) from the family-wide PAINT node PTN001219785, seeded by Drosophila Gprk and a human GRK. Reason: Not wrong - the outer-segment disc membranes where opsin kinases act lie within the cytoplasm - but grk7b is a C-terminally geranylgeranylated membrane-anchored kinase (UniProt LIPID feature; SUBCELLULAR LOCATION Membrane), so the informative location is the membrane, already annotated. Kept as non-core; no target-specific reason to contest the node placement. Supporting Evidence: file:DANRE/grk7b/grk7b-uniprot.txt SUBCELLULAR LOCATION: Membrane file:DANRE/grk7b/grk7b-uniprot.txt /note="S-geranylgeranyl cysteine" |
| GO:0009966 regulation of signal transduction | IBA GO_REF:0000033 | ACCEPT | Summary: Regulation of signal transduction, placed by PAINT at the GRK-family node PTN001219785 (GRK1-7 across vertebrates and Drosophila Gprk). Reason: At the family node the term is correct: every GRK phosphorylates activated GPCRs to desensitise signalling, and grk7b phosphorylates light-activated rhodopsin in vitro [PMID:16787417], consistent with the UniProt FUNCTION (photoresponse shutoff via cone opsin phosphorylation). The specific child that human GRK7 carries, GO:0016059 negative regulation of opsin-mediated signaling pathway, is not proposed for grk7b because the only in vivo test of this paralog (pineal parapinopsin inactivation) was negative [PMID:33579376] and the retinal in vivo work concerns grk7a [PMID:16039565]. Accepted at the node's level of specificity. Supporting Evidence: file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). PMID:16787417 we focused on the opsin deactivation process initiated by G protein-coupled receptor kinase (GRK) 1 and GRK7 in the zebrafish PMID:33579376 We found that GRK7a knockdown slowed recovery of the response of parapinopsin photoreceptor cells, whereas GRK1b knockdown or GRK7b knockdown did not have a remarkable effect, suggesting that GRK7a, a cone-type GRK, is mainly responsible for inactivation of the parapinopsin photoproduct in zebrafish larvae. file:DANRE/grk7b/grk7b-deep-research-falcon.md A high-confidence, gene-specific finding is that **grk7b is enriched in adult UV cones**. |
| GO:0050254 rhodopsin kinase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Rhodopsin kinase activity (EC 2.7.11.14): ATP-dependent phosphorylation of light-activated opsin. grk7b is GRK7-2 of Wada et al., one of the two zebrafish GRK7 paralogs. Reason: PAINT node PTN002806910 (GRK1/GRK7 subfamily, seeded by human GRK7 Q8WTQ7 and both zebrafish grk7 paralogs) is the right node, and grk7b has its own IDA from the same source paper, so the target appearing in WITH/FROM is expected. Core activity [PMID:16787417]. Supporting Evidence: PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). |
| GO:0004672 protein kinase activity | IEA GO_REF:0000002 | MODIFY | Summary: protein kinase activity: broad kinase parent term from InterPro/ARBA signatures (protein kinase domain, AGC kinase, GPCR-kinase family). Reason: Correct but uninformative; the specific activity demonstrated for the zebrafish protein is rhodopsin kinase activity [PMID:16787417], already annotated by IDA/IBA. Modify to GO:0050254. Proposed replacements: rhodopsin kinase activity Supporting Evidence: PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). |
| GO:0004674 protein serine/threonine kinase activity | IEA GO_REF:0000002 | MODIFY | Summary: protein serine/threonine kinase activity: broad kinase parent term from InterPro/ARBA signatures (protein kinase domain, AGC kinase, GPCR-kinase family). Reason: Correct but uninformative; the specific activity demonstrated for the zebrafish protein is rhodopsin kinase activity [PMID:16787417], already annotated by IDA/IBA. Modify to GO:0050254. Proposed replacements: rhodopsin kinase activity Supporting Evidence: PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: ATP binding from the protein-kinase ATP-binding-site signatures (IPR000719/IPR017441); UniProt annotates the ATP-binding loop (193-201) and Lys-216. Reason: True of any active kinase and required for the rhodopsin-phosphorylation reaction [PMID:16787417], but it is a substrate-binding descriptor rather than the function. Kept as non-core. Supporting Evidence: PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). |
| GO:0007165 signal transduction | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: Signal transduction from the GPCR-kinase InterPro signature (IPR000239). Reason: GRK7 kinases terminate rather than transmit the opsin signal; the gene's role is captured by the accepted regulation-of-signal-transduction IBA and by rhodopsin kinase activity [PMID:16787417]. The broad process term is not false but adds nothing and over-states an 'involved_in' role in signalling itself; marked over-annotated rather than removed. Supporting Evidence: file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). PMID:16787417 we focused on the opsin deactivation process initiated by G protein-coupled receptor kinase (GRK) 1 and GRK7 in the zebrafish |
| GO:0016020 membrane | IEA GO_REF:0000044 | ACCEPT | Summary: Membrane, lipid-anchored: UniProt SUBCELLULAR LOCATION by similarity to carp GRK7 (Q8WMV0), with a C-terminal S-geranylgeranyl cysteine. Reason: UniProtKB-SubCell SL-0162 mapping. Consistent with the prenylation site and with GRK7 paralogs acting on opsins in photoreceptor outer-segment membranes; the zebrafish immunolocalisation of GRK7-1 to cone outer segments [PMID:16787417] and the anti-Grk7 antibody used later recognises both paralogs [PMID:30372740], so paralog-specific localisation of Grk7b itself remains to be shown. Accepted as the core site of action. Supporting Evidence: file:DANRE/grk7b/grk7b-uniprot.txt SUBCELLULAR LOCATION: Membrane file:DANRE/grk7b/grk7b-uniprot.txt /note="S-geranylgeranyl cysteine" PMID:16787417 In situ hybridization and immunohistochemical studies localized both GRK1B and GRK7-1 in the cone outer segments and GRK1A in the rod outer segments. |
| GO:0050254 rhodopsin kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Rhodopsin kinase activity (EC 2.7.11.14): ATP-dependent phosphorylation of light-activated opsin. grk7b is GRK7-2 of Wada et al., one of the two zebrafish GRK7 paralogs. Reason: Rhea:23356/EC 2.7.11.14 mapping of the UniProt CATALYTIC ACTIVITY, which is itself experimentally sourced from the zebrafish recombinant-kinase assay [PMID:16787417]. Core activity. Supporting Evidence: file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. |
| GO:0016020 membrane | ISS GO_REF:0000024 | ACCEPT | Summary: Membrane, lipid-anchored: UniProt SUBCELLULAR LOCATION by similarity to carp GRK7 (Q8WMV0), with a C-terminal S-geranylgeranyl cysteine. Reason: Transfer from carp GRK7 (Q8WMV0). Consistent with the prenylation site and with GRK7 paralogs acting on opsins in photoreceptor outer-segment membranes; the zebrafish immunolocalisation of GRK7-1 to cone outer segments [PMID:16787417] and the anti-Grk7 antibody used later recognises both paralogs [PMID:30372740], so paralog-specific localisation of Grk7b itself remains to be shown. Accepted as the core site of action. Supporting Evidence: file:DANRE/grk7b/grk7b-uniprot.txt SUBCELLULAR LOCATION: Membrane file:DANRE/grk7b/grk7b-uniprot.txt /note="S-geranylgeranyl cysteine" PMID:16787417 In situ hybridization and immunohistochemical studies localized both GRK1B and GRK7-1 in the cone outer segments and GRK1A in the rod outer segments. |
| GO:0050254 rhodopsin kinase activity | ISS GO_REF:0000024 | ACCEPT | Summary: Rhodopsin kinase activity (EC 2.7.11.14): ATP-dependent phosphorylation of light-activated opsin. grk7b is GRK7-2 of Wada et al., one of the two zebrafish GRK7 paralogs. Reason: Manual transfer from human GRK7 (Q8WTQ7); redundant with, and consistent with, the direct zebrafish assay [PMID:16787417]. Core activity. Supporting Evidence: PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). |
| GO:0050254 rhodopsin kinase activity | IDA PMID:16787417 GRK1 and GRK7: unique cellular distribution and widely diffe... | ACCEPT | Summary: Rhodopsin kinase activity (EC 2.7.11.14): ATP-dependent phosphorylation of light-activated opsin. grk7b is GRK7-2 of Wada et al., one of the two zebrafish GRK7 paralogs. Reason: Abstract-only cache, but the abstract states that the recombinant zebrafish GRKs (which include GRK7-2 = grk7b) phosphorylated light-activated rhodopsin, and UniProt records both Rhea reactions for Q1XHL7 from this paper (ECO:0000269). Core activity. In vivo, grk7b knockdown had no remarkable effect on parapinopsin photoresponse inactivation in the pineal, whereas grk7a knockdown did [PMID:33579376], and the retinal cone-recovery phenotypes are grk7a knockdowns [PMID:16039565]; grk7b is the UV-cone-enriched paralog [PMID:34462505]. Supporting Evidence: PMID:16787417 Screening of the ocular cDNAs identified two homologs for each of GRK1 (1A and 1B) and GRK7 (7-1 and 7-2), and they were classified into three GRK subfamilies, 1 A, 1B and 7 by phylogenetic analysis. PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). |
| GO:0004703 G protein-coupled receptor kinase activity | IEA GO_REF:0000120 | MODIFY | Summary: G protein-coupled receptor kinase activity: broad kinase parent term from InterPro/ARBA signatures (protein kinase domain, AGC kinase, GPCR-kinase family). Reason: Correct but uninformative; the specific activity demonstrated for the zebrafish protein is rhodopsin kinase activity [PMID:16787417], already annotated by IDA/IBA. Modify to GO:0050254. Proposed replacements: rhodopsin kinase activity Supporting Evidence: PMID:16787417 The recombinant GRKs phosphorylated light-activated rhodopsin, and the Vmax value of the major cone subtype, GRK7-1, was 32-fold higher than that of the rod kinase, GRK1A. file:DANRE/grk7b/grk7b-uniprot.txt Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). |
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Download this section (compressed HTML)Q: Does grk7b loss delay photoresponse recovery specifically in UV cones, where it is the enriched GRK7 paralog, or does grk7a compensate?
Q: What are the kinetic parameters of recombinant Grk7b on UV opsin (opn1sw1) versus rhodopsin, and how do they compare with Grk7a?
Experiment: Generate a grk7b CRISPR mutant and record UV-cone-isolated electroretinograms (and grk7a/grk7b double mutants) to test whether Grk7b contributes to cone response recovery in the UV cone subtype.
Hypothesis: Grk7b is required for rapid photoresponse shutoff in UV cones, a role masked in whole-retina recordings dominated by grk7a-expressing cones.
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