id: Q8UUX9
gene_symbol: guca1c
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:7955
  label: Danio rerio
description: guca1c (guanylate cyclase activator 1C; protein name zGCAP3) is one of two zebrafish co-orthologs
  of vertebrate GUCA1C (GCAP3), retained from the teleost-specific genome duplication; its paralog is guca1d (zGCAP4).
  It encodes a small (188 aa) N-myristoylated neuronal calcium sensor of the recoverin/GCAP family with four EF-hands,
  of which EF2-EF4 bind Ca2+. Like other GCAPs it activates the photoreceptor membrane guanylate cyclases at low free
  Ca2+ and inhibits them at high Ca2+, so it mediates the Ca2+ feedback that restores cGMP after light exposure. Among
  the zebrafish GCAPs it activates the cyclases with high Ca2+ sensitivity (half-maximal near 30 nM free Ca2+,
  similar to zGCAP1 and zGCAP2 and more than tenfold lower than zGCAP4). guca1c is expressed in all four cone
  types and not in rods, from about 3-4 dpf; it is the most abundant GCAP transcript in adult cones and is present
  in large molar excess over the cone cyclase zGC3. Morpholino knockdown did not change larval optokinetic or
  optomotor responses, and a CRISPR knockout reported Muller-cell gliosis and some ganglion-cell apoptosis.
existing_annotations:
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  supporting_entities:
  - FB:FBgn0013303
  - FB:FBgn0030897
  - FB:FBgn0083228
  - MGI:MGI:1929258
  - MGI:MGI:1933131
  - MGI:MGI:97883
  - PANTHER:PTN000550679
  - PomBase:SPAC18B11.04
  - RGD:620060
  - RGD:620258
  - RGD:68417
  - RGD:70886
  - RGD:70887
  - UniProtKB:P46065
  - UniProtKB:P84074
  - UniProtKB:Q6PIL6
  - UniProtKB:Q8T893
  - UniProtKB:Q9NZI2
  - ZFIN:ZDB-GENE-011128-6
  - ZFIN:ZDB-GENE-030829-1
  - ZFIN:ZDB-GENE-040724-231
  - ZFIN:ZDB-GENE-050120-1
  - dictyBase:DDB_G0270210
  - dictyBase:DDB_G0275931
  review:
    summary: Calcium ion binding, propagated from the neuronal calcium sensor node of the recoverin/GCAP family.
    action: ACCEPT
    reason: Correct and directly confirmed for this protein. zGCAP3 binds three Ca2+ ions with high affinity, and its
      EF2-EF4 loops keep the Ca2+-coordinating residues annotated on human GUCA1C (bioinformatics RESULTS.md). guca1c
      (ZFIN:ZDB-GENE-030829-1) appears among the IBA sources because it has its own experimental annotation.
    supported_by:
    - &ca3
      reference_id: PMID:26061947
      supporting_text: In all zGCAPs at least two binding sites exhibited high affinities for Ca2+ with KD values
        in the submicromolar range (KD1 and KD2 in Table 2), for zGCAP3 also the third site (KD3) showed high affinity
        for Ca2+, whereas for other zGCAPs the affinity of KD3 was in the micromolar range.
    - &bioinf
      reference_id: file:DANRE/guca1c/guca1c-bioinformatics/RESULTS.md
      supporting_text: All 14 Ca2+-coordinating positions annotated on human GUCA1C (EF2, EF3 and EF4 loops) align
        to residues compatible with Ca2+ binding in both zebrafish copies
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IDA
  original_reference_id: PMID:11860507
  qualifier: enables
  review:
    summary: Calcium ion binding shown by the Ca2+-dependent electrophoretic mobility shift of recombinant zGCAP3.
    action: ACCEPT
    reason: The mobility shift is a standard indication of Ca2+ binding by GCAPs, and later titrations measured the
      binding directly.
    supported_by:
    - reference_id: PMID:11860507
      supporting_text: zGCAP3 displayed a minor mobility change in the presence and absence of Ca 2+ , as observed
        for other GCAPs
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IDA
  original_reference_id: PMID:21829700
  qualifier: enables
  review:
    summary: Direct Ca2+ titration of recombinant zGCAP3.
    action: ACCEPT
    reason: Direct binding measurement; all six zebrafish GCAPs bind at least three Ca2+ ions.
    supported_by:
    - reference_id: PMID:21829700
      supporting_text: Direct Ca(2+)-binding revealed that all zGCAPs bound at least three Ca(2+).
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IDA
  original_reference_id: PMID:26061947
  qualifier: enables
  review:
    summary: Isothermal titration calorimetry and SPR of zGCAP3 Ca2+ binding.
    action: ACCEPT
    reason: Direct measurement; zGCAP3 is the only zebrafish GCAP in which all three sites bind Ca2+ with high
      affinity.
    supported_by:
    - *ca3
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  supporting_entities:
  - InterPro:IPR002048
  - InterPro:IPR028846
  - UniRule:UR001552760
  review:
    summary: Calcium ion binding from EF-hand and recoverin-family InterPro signatures.
    action: ACCEPT
    reason: Correct; confirmed experimentally for this protein.
    supported_by:
    - *ca3
- term:
    id: GO:0005509
    label: calcium ion binding
  evidence_type: ISS
  original_reference_id: PMID:15486694
  qualifier: enables
  supporting_entities:
  - UniProtKB:P51177
  review:
    summary: Calcium ion binding by sequence similarity, from the comparative analysis of teleost GCAPs.
    action: ACCEPT
    reason: Correct; the paper notes three functional EF-hands in all GCAPs, and binding was later measured directly.
    supported_by:
    - reference_id: PMID:15486694
      supporting_text: Sequence analysis of the predicted polypeptides identified a myristoylation site at position
        2 and three functional EF-hand Ca 2+ -binding motifs, EF2-4, characteristic of all GCAPs.
- term:
    id: GO:0008048
    label: calcium sensitive guanylate cyclase activator activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  supporting_entities:
  - PANTHER:PTN002746644
  - ZFIN:ZDB-GENE-030829-1
  - ZFIN:ZDB-GENE-040724-231
  review:
    summary: Calcium-sensitive guanylate cyclase activator activity, from the PANTHER GCAP3 node seeded by the two
      zebrafish co-orthologs.
    action: ACCEPT
    reason: Core molecular function. The node's donors are guca1c itself and its paralog guca1d, both of which have
      experimental annotations for this activity; the target appearing among its own sources is expected.
    supported_by:
    - &ic50
      reference_id: PMID:21829700
      supporting_text: The IC50 values of zGCAPs could be separated in two groups; one group consisting of zGCAP1,
        2, and 3 had IC50 values around 30 nM free [Ca2+], the second group of zGCAP4, 5 and 7 had IC50 values between
        180 and 520 nM centered around 400 nM (Table 2 and Figure 3).
- term:
    id: GO:0008048
    label: calcium sensitive guanylate cyclase activator activity
  evidence_type: IDA
  original_reference_id: PMID:11860507
  qualifier: enables
  review:
    summary: Recombinant zGCAP3 stimulated bovine rod outer segment guanylate cyclase at low Ca2+ and inhibited it
      at high Ca2+.
    action: ACCEPT
    reason: Direct enzymatic assay showing the defining Ca2+-dependent activation.
    supported_by:
    - reference_id: PMID:11860507
      supporting_text: In the GC assay, GCAPs display the expected properties, modulating ROS GCs in a Ca 2+ -dependent
        manner stimulating at low and inhibiting at high [Ca 2+ ] ( Fig. 9B ).
- term:
    id: GO:0008048
    label: calcium sensitive guanylate cyclase activator activity
  evidence_type: IDA
  original_reference_id: PMID:21829700
  qualifier: enables
  review:
    summary: Ca2+-dependent activation of membrane guanylate cyclase by purified zGCAP3, with IC50 near 30 nM free
      Ca2+.
    action: ACCEPT
    reason: Direct assay comparing all six zebrafish GCAPs; zGCAP3 is a strong activator with high Ca2+ sensitivity.
    supported_by:
    - reference_id: PMID:21829700
      supporting_text: Isoforms 1-4 were strong, 5 and 7 were weak activators of membrane bound guanylate cyclase.
    - *ic50
- term:
    id: GO:0008048
    label: calcium sensitive guanylate cyclase activator activity
  evidence_type: IDA
  original_reference_id: PMID:22212098
  qualifier: enables
  review:
    summary: Myristoylated and non-myristoylated zGCAP3 regulate a membrane guanylate cyclase (abstract only in
      cache).
    action: ACCEPT
    reason: The abstract reports that both forms modulate the cyclase, with different kinetic parameters; consistent
      with the other assays.
    supported_by:
    - reference_id: PMID:22212098
      supporting_text: Differences between myristoylated and non-myristoylated zGCAP3 were also observed in modulating
        the kinetic and catalytic parameters of the GCAP-target, a membrane bound guanylate cyclase.
- term:
    id: GO:0008048
    label: calcium sensitive guanylate cyclase activator activity
  evidence_type: IDA
  original_reference_id: PMID:23940527
  qualifier: enables
  review:
    summary: Myristoylated zGCAP3 activated guanylate cyclases in native adult zebrafish retinal membranes in a
      Ca2+-dependent way.
    action: ACCEPT
    reason: Assay with the native zebrafish cyclases; zGCAP3 gave the highest activities of the cone GCAPs tested.
    supported_by:
    - &native
      reference_id: PMID:23940527
      supporting_text: The highest activities were measured with zGCAP3 indicating that zGCAP3 is indeed a major
        activator of zGCs in native zebrafish retinae.
- term:
    id: GO:0009966
    label: regulation of signal transduction
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  supporting_entities:
  - FB:FBgn0013303
  - PANTHER:PTN008588905
  - RGD:68417
  - SGD:S000002781
  review:
    summary: Regulation of signal transduction, propagated from a deep neuronal calcium sensor node.
    action: KEEP_AS_NON_CORE
    reason: Broadly true, since GCAP-mediated cyclase activation feeds back on cone phototransduction, but the term
      is very general and was placed for the whole NCS family. The specific process is the Ca2+-dependent positive
      regulation of guanylate cyclase activity, recorded in core_functions. No in vivo phototransduction measurement
      exists for guca1c.
    supported_by:
    - reference_id: PMID:21829700
      supporting_text: Light causes a drop of intracellular Ca2+, which triggers activation of membrane bound guanylate
        cyclases (GC) in rod and cone cells.
- term:
    id: GO:0030250
    label: guanylate cyclase activator activity
  evidence_type: ISS
  original_reference_id: PMID:15486694
  qualifier: enables
  supporting_entities:
  - UniProtKB:P43080
  review:
    summary: Guanylate cyclase activator activity by similarity to human GCAP1.
    action: ACCEPT
    reason: Correct parent of the experimentally supported calcium-sensitive term; zGCAP3 activates the cyclase
      in direct assays.
    supported_by:
    - reference_id: PMID:15486694
      supporting_text: Recombinant zGCAP3 was previously shown to stimulate bovine GC, suggesting conservation of
        residues critically important for interaction between partners of distantly related species.
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:11860507
  title: Characterization of retinal guanylate cyclase-activating protein 3 (GCAP3) from zebrafish to man.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Full text. Cloning of zGCAP1-3; zGCAP3 activates bovine ROS GC Ca2+-dependently; in situ shows
      zGCAP3 in all cone types, not rods.
- id: PMID:15486694
  title: 'Diversity of guanylate cyclase-activating proteins (GCAPs) in teleost fish: characterization of three novel
    GCAPs (GCAP4, GCAP5, GCAP7) from zebrafish (Danio rerio) and prediction of eight GCAPs (GCAP1-8) in pufferfish
    (Fugu rubripes).'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Full text. Defines the GCAP4-8 names; mainly about the paralog guca1d (zGCAP4). Retina-specific
      RT-PCR of all zGCAPs.
- id: PMID:21829700
  title: Differential calcium signaling by cone specific guanylate cyclase-activating proteins from the zebrafish
    retina.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Full text. Side-by-side assay of all six zGCAPs; zGCAP3 IC50 about 30 nM versus about 400 nM for
      zGCAP4.
- id: PMID:22212098
  title: Operation profile of zebrafish guanylate cyclase-activating protein 3.
  findings: []
  full_text_unavailable: true
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Abstract only. zGCAP3 immunolocalization (cone inner segments, plexiform layers) and myristoylation
      from larval to adult stages.
- id: PMID:23940527
  title: Zebrafish guanylate cyclase type 3 signaling in cone photoreceptors.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Full text. zGCAP3 activates native retinal cyclases; morpholino knockdown gives no OKR or OMR
      defect; authors suggest compensation by zGCAP4.
- id: PMID:26061947
  title: Retina specific GCAPs in zebrafish acquire functional selectivity in Ca2+-sensing by myristoylation and
    Mg2+-binding.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Full text. Ca2+ affinities of all zGCAPs; zGCAP3 has three high-affinity sites.
- id: PMID:19168097
  title: Expression profiles of three novel sensory guanylate cyclases and guanylate cyclase-activating proteins
    in the zebrafish retina.
  findings: []
  full_text_unavailable: true
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Abstract only. zGCAP3, zGCAP4 and zGCAP7 transcripts appear at 3-4 dpf, with the cyclases.
- id: PMID:30257895
  title: Evolution of the calcium feedback steps of vertebrate phototransduction.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Full text. Identifies zGCAP3 and zGCAP4 as the teleost 3R duplicates of GCAP3; GCAP3 transcripts
      present in gar and bowfin retina.
- id: PMID:32422965
  title: 'Role of GUCA1C in Primary Congenital Glaucoma and in the Retina: Functional Evaluation in Zebrafish.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: LOW_QUALITY
    review_notes: Full text. CRISPR guca1c knockout (NMD-type allele, mRNA below 40% of wild type) with gliosis
      and ganglion-cell apoptosis. The immunostaining used an anti-human GUCA1C antibody; its signals disappear in
      the knockout, but it labels rods as well as cones, which conflicts with cone-only in situ and single-cell
      transcript data. Possible guca1d compensation was not tested, and the phenotype is modest and not linked to
      cone function.
- id: PMID:34462505
  title: Partitioning of gene expression among zebrafish photoreceptor subtypes.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: Full text. Adult photoreceptor scRNA-seq (GSE175929); reanalysed for guca1c/guca1d in the bioinformatics
      folder.
- id: file:DANRE/guca1c/guca1c-bioinformatics/RESULTS.md
  title: guca1c / guca1d sequence, synteny and expression analysis
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: Manual audit verified the sidecar supports both GCAP3 duplicates retaining GCAP architecture and
      calcium-binding features while documenting cone expression and higher guca1c abundance.
  findings: []
core_functions:
- description: Myristoylated neuronal Ca2+ sensor of cone photoreceptors that activates the photoreceptor membrane
    guanylate cyclases when free Ca2+ falls and inhibits them at high Ca2+; the high-Ca2+-sensitivity member of the
    zebrafish GCAP set, expressed in all cone types.
  molecular_function:
    id: GO:0008048
    label: calcium sensitive guanylate cyclase activator activity
  supported_by:
  - *ic50
  - *native
  - reference_id: PMID:22212098
    supporting_text: Using affinity purified antibodies immunoreactivity towards zGCAP3 was weakly detected in the
      outer and strongly in the inner segments of cone cells as well as in the outer plexiform layer, to a lesser
      degree also in the inner plexiform and ganglion cell layer of the zebrafish retina.
suggested_questions:
- question: Is the tenfold difference in Ca2+ sensitivity between zGCAP3 (guca1c) and zGCAP4 (guca1d) derived in
    one copy, and which copy resembles gar GCAP3 when assayed in the same system?
- question: Does guca1d compensate in guca1c mutants (transcriptional adaptation after the NMD-type allele), and
    does a guca1c; guca1d double mutant alter cone photoresponse recovery?
- question: Are the plexiform-layer and ganglion-cell-layer immunosignals for zGCAP3 real, or cross-reactivity, given
    that single-cell and in situ data restrict the transcript to cones?
suggested_experiments:
- hypothesis: guca1c and guca1d are partly redundant in cone Ca2+ feedback.
  description: Generate guca1c and guca1d single and double mutants (ideally promoter-less or RNA-less alleles to
    avoid transcriptional adaptation) and record cone ERG a-wave recovery and paired-flash recovery in larvae and adults.
  experiment_type: double mutant electrophysiology
- hypothesis: The Ca2+ sensitivity difference between the copies is a protein-level divergence from the ancestral
    GCAP3.
  description: Express spotted gar GCAP3 alongside zGCAP3 and zGCAP4 and measure GC activation versus free Ca2+ with
    the same native zebrafish retinal membranes.
  experiment_type: in vitro enzyme assay