Affinage

CNGA2

Cyclic nucleotide-gated channel alpha-2 · UniProt Q16280

Length
664 aa
Mass
76.0 kDa
Annotated
2026-06-09
13 papers in source corpus 9 papers cited in narrative 9 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

CNGA2 is a cyclic nucleotide-gated cation channel that serves as the principal effector of olfactory signal transduction, converting odorant-evoked cAMP into depolarizing cation influx (PMID:10531436). The channel assembles as a homotetramer whose pore-loop glutamate E342 is the central functional determinant: neutralizing or charge-reversing this residue switches the channel from cation- to anion-selective and abolishes its voltage-dependence and state-dependent pore block, identifying E342 as the key pore-lining residue positioned within the transmembrane electric field (PMID:16533895, PMID:15928936). Channel gating is not symmetric — fully and partially liganded channels traverse distinct activation and deactivation pathways, producing concentration-dependent hysteresis in which ligand unbinding accelerates dramatically at saturating ligand concentrations (PMID:24287615). Beyond ion conduction, CNGA2 activity drives the biology of olfactory sensory neurons: it is required for normal maturation of the olfactory epithelium and bulb (PMID:10531436) and for the activity-dependent competitive survival of sensory neurons, such that CNGA2-deficient neurons are selectively eliminated in an odorant-exposure-dependent manner (PMID:11257220). This survival role is embedded in a homeostatic feedback loop in which channel activity governs axonal convergence and the expression of the retinoic acid-degrading enzyme Cyp26B1 (PMID:22009938). CNGA2 also functions outside olfaction as a cAMP-gated Ca2+ entry pathway in vascular endothelium downstream of adenosine A2B and ATP/P2Y1 receptors coupled to adenylyl cyclase (PMID:18292397, PMID:19729961), and in carotid body glomus cells downstream of an Adcy3-dependent cAMP signaling axis [PMID:bio_10.1101_2024.09.24.614747].

Mechanistic history

Synthesis pass · year-by-year structured walk · 9 steps
  1. 1999 High

    Established that CNGA2 is indispensable for olfactory signal transduction and for activity-driven maturation of the olfactory system, defining its core physiological role.

    Evidence Targeted knockout mice analyzed by morphology, biochemistry, and immunohistochemistry (OMP, GAP-43, TH, bulb size)

    PMID:10531436

    Open questions at the time
    • Does not resolve the channel's biophysical gating or conduction mechanism
    • Does not distinguish developmental from maintenance requirements at single-neuron resolution
  2. 2001 High

    Showed that evoked activity through CNGA2 dictates competitive survival of olfactory sensory neurons, linking channel function to neuronal selection rather than just signaling.

    Evidence Reporter-tagged Cnga2 mutant mice with X-inactivation mosaic analysis and reversible odorant deprivation/exposure

    PMID:11257220

    Open questions at the time
    • Downstream molecular effectors translating channel activity into survival not identified
    • Mechanism of competition between neurons unresolved
  3. 2005 High

    Identified pore glutamate E342 as the determinant of voltage-dependence and state-dependent pore block, locating it within the transmembrane electric field.

    Evidence E342Q mutagenesis with inside-out patch-clamp dequalinium block analysis in HEK293 cells expressing rat CNGA2

    PMID:15928936

    Open questions at the time
    • No high-resolution structure of the pore
    • Block determinants for endogenous physiological blockers not addressed
  4. 2006 High

    Demonstrated that the charge of E342, not pore-helix dipoles, sets cation-anion selectivity, defining the molecular basis of ion discrimination.

    Evidence E342K/R mutagenesis with reversal-potential and bi-ionic substitution patch-clamp in HEK293 cells

    PMID:16533895

    Open questions at the time
    • Structural geometry of the selectivity filter not resolved
    • Contribution of other subunit residues to selectivity not tested
  5. 2008 Medium

    Extended CNGA2 function beyond olfaction by showing it mediates adenosine A2B/adenylyl cyclase-driven Ca2+ influx in vascular endothelium.

    Evidence CNGA2 siRNA knockdown, patch-clamp, Ca2+ imaging, and pharmacology in endothelial cells and mouse aortic strips

    PMID:18292397

    Open questions at the time
    • Knockdown specificity not confirmed by genetic knockout in this system
    • Native channel subunit composition in endothelium unknown
  6. 2009 Medium

    Showed CNGA2 also supports ATP/P2Y1-evoked non-capacitative Ca2+ entry via adenylyl cyclase, generalizing its endothelial Ca2+-signaling role across agonists.

    Evidence CNGA2 siRNA knockdown, Ca2+ imaging, and receptor/cyclase pharmacology in endothelial cells and aortic strips

    PMID:19729961

    Open questions at the time
    • Relies on siRNA and pharmacology without genetic validation
    • Physiological consequence for vascular tone not fully established
  7. 2011 Medium

    Placed CNGA2 in a homeostatic feedback loop with retinoic acid metabolism controlling axonal convergence and survival, mechanistically connecting channel activity to circuit wiring.

    Evidence Cnga2-deficient and dominant-negative RAR mice, naris occlusion, immunohistochemistry, and Cyp26B1 expression analysis

    PMID:22009938

    Open questions at the time
    • Direct molecular link from channel activity to Cyp26B1 transcription not defined
    • Single-lab finding without independent confirmation
  8. 2013 High

    Revealed concentration-dependent gating hysteresis with distinct activation and deactivation pathways, refining the kinetic mechanism of ligand gating in the homotetramer.

    Evidence Fluorescent cGMP binding assay combined with patch-clamp and Markovian kinetic modeling of homotetrameric CNGA2

    PMID:24287615

    Open questions at the time
    • Structural correlates of the distinct open states not resolved
    • Behavior in heteromeric native channels not addressed
  9. 2024 Medium

    Implicated CNGA2 in carotid body chemosensing downstream of an Adcy3-dependent cAMP axis, suggesting a broader role in cAMP-driven Ca2+ signaling in chemoreceptor cells.

    Evidence Cnga2 knockout mice with glomus cell Ca2+ imaging under chronic intermittent hypoxia, compared with Adcy3 and Olfr78 mutants (preprint)

    PMID:bio_10.1101_2024.09.24.614747

    Open questions at the time
    • Preprint, single lab
    • Epistasis inferred from parallel mutant comparisons rather than direct manipulation

Open questions

Synthesis pass · forward-looking unresolved questions
  • How CNGA2's biophysically defined gating and conduction properties are coupled to its in vivo roles in neuronal survival, axon guidance, and vascular/chemoreceptor Ca2+ signaling remains unresolved at the structural and molecular-effector level.
  • No atomic structure linking E342 and gating states to function
  • Downstream effectors of CNGA2-dependent Ca2+ in survival and axonal convergence unidentified
  • Native subunit composition across non-olfactory tissues undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005215 transporter activity 6 GO:0060089 molecular transducer activity 3
Localization
GO:0005886 plasma membrane 3
Pathway
R-HSA-112316 Neuronal System 3 R-HSA-162582 Signal Transduction 3 R-HSA-9709957 Sensory Perception 2
Complex memberships
CNGA2 homotetrameric channel

Evidence

Reading pass · 9 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1999 OCNC1 (CNGA2) is required for olfactory signal transduction: knockout mice showed thinner olfactory epithelium with reduced olfactory marker protein and GAP-43 expression, smaller olfactory bulbs, and reduced tyrosine hydroxylase in periglomerular neurons, indicating CNGA2 is essential for normal development and afferent-activity-driven maturation of both olfactory epithelium and olfactory bulb. Targeted gene knockout with morphological, biochemical, and immunohistochemical analysis in adult null mice The Journal of neuroscience High 10531436
2001 CNGA2-mediated olfactory activity is required for competitive survival of olfactory sensory neurons: in heterozygous females with mosaic X-inactivation, CNGA2-deficient neurons were selectively depleted from the olfactory epithelium upon odorant exposure, and this depletion was reversed by odorant deprivation, demonstrating that evoked activity through CNGA2 is critical for neuronal survival in a competitive environment. Reporter-tagged OCNC1 (CNGA2) mutant mice; X-inactivation mosaic analysis; odorant deprivation/exposure experiments with histological readout Cell High 11257220
2006 The pore-loop glutamate E342 of CNGA2 is the primary determinant of cation-anion selectivity: point mutation of E342 to lysine or arginine switched the channel from cation-selective (P_Cl/P_Na = 0.07) to anion-selective (P_Cl/P_Na = 14 or 10), demonstrating that the charge of this residue, rather than pore-helix dipoles, controls ion selectivity. Site-directed mutagenesis; inside-out patch-clamp with reversal potential measurements and bi-ionic substitution experiments in HEK293 cells expressing rat CNGA2 The Journal of general physiology High 16533895
2005 Pore glutamate E342 of CNGA2 controls voltage-dependence, state-dependence, and both cytoplasmic and external dequalinium block: neutralizing E342 (E342Q) drastically reduced voltage-dependence (zdelta from +0.8 to +0.1), abolished state-dependent block (WT prefers closed state; mutant is state-independent), and increased external dequalinium IC50 ~5-fold, placing E342 about two-fifths along the transmembrane electric field as a key pore-lining residue. Site-directed mutagenesis (E342Q); inside-out patch-clamp; concentration-response and voltage-dependence analysis of dequalinium block in HEK293 cells expressing rat CNGA2 European biophysics journal High 15928936
2008 CNGA2 mediates adenosine-induced Ca2+ influx in vascular endothelial cells via A2B receptors and adenylyl cyclase: adenosine-induced Ca2+ influx and cation current were blocked by CNG channel inhibitors (L-cis-diltiazem, LY-83583) and adenylyl cyclase inhibitors, but not by guanylyl cyclase inhibitor ODQ; CNGA2-specific siRNA markedly reduced both Ca2+ influx and current; L-cis-diltiazem also inhibited NECA-induced vasorelaxation in mouse aortic strips. CNGA2-specific siRNA knockdown; patch-clamp; Ca2+ fluorescence imaging; pharmacological inhibitors in H5V endothelial cells, primary bovine aortic endothelial cells, and mouse aortic strips Arteriosclerosis, thrombosis, and vascular biology Medium 18292397
2009 CNGA2 contributes to ATP-induced non-capacitative Ca2+ entry in vascular endothelial cells via P2Y1 receptors and adenylyl cyclase: CNG channel inhibitors (L-cis-diltiazem, LY-83583) and CNGA2-specific siRNA reduced ATP-induced non-CCE; the effect was blocked by adenylyl cyclase inhibitors and P2Y1 inhibitor MRS-2179, but not by guanylyl cyclase inhibitor ODQ. CNGA2-specific siRNA knockdown; Ca2+ fluorescence imaging; pharmacological inhibitors in H5V cells, primary bovine aortic endothelial cells, and isolated mouse aortic strips Journal of vascular research Medium 19729961
2011 CNGA2 channel activity regulates axonal convergence and neuronal survival of olfactory sensory neurons through a feedback loop with retinoic acid metabolism: CNG channel-deficient mice showed defective axonal convergence and increased cell death; retinoic acid receptor inhibition reduced CNG channel expression; CNG channel activity in turn regulated expression of the RA-degrading enzyme Cyp26B1, establishing a homeostatic feedback mechanism. CNG channel-deficient (Cnga2) mice; dominant-negative RAR transgenic mice; naris occlusion; immunohistochemistry; gene expression analysis FASEB journal Medium 22009938
2013 CNGA2 homotetrameric channels exhibit concentration-dependent gating hysteresis: ligand unbinding is ~50-fold faster at saturating than subsaturating fcGMP concentrations; Markovian modeling revealed two unbinding pathways—partially liganded open channels unbind from closed states only, while fully liganded channels reach a distinct open state from which all four ligands unbind rapidly—resulting in different transition pathways for activation versus deactivation. Fluorescent cGMP derivative (fcGMP) binding assay; patch-clamp electrophysiology; complex Markovian kinetic modeling of homotetrameric CNGA2 channels Nature communications High 24287615
2024 CNGA2 mediates CIH-induced enhanced Ca2+ influx in carotid body glomus cells downstream of Adcy3-dependent cAMP: CIH-induced glomus cell Ca2+ responses were absent in Cnga2 mutant mice, placing CNGA2 downstream of the Olfr78/H2S/Adcy3/cAMP signaling axis in carotid body activation. Cnga2 knockout mice; glomus cell Ca2+ imaging under chronic intermittent hypoxia (CIH) protocol; comparison with Adcy3 and Olfr78 mutants bioRxiv (preprint)preprint Medium bio_10.1101_2024.09.24.614747

Source papers

Stage 0 corpus · 13 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2001 X inactivation of the OCNC1 channel gene reveals a role for activity-dependent competition in the olfactory system. Cell 165 11257220
1999 Targeted deletion of a cyclic nucleotide-gated channel subunit (OCNC1): biochemical and morphological consequences in adult mice. The Journal of neuroscience : the official journal of the Society for Neuroscience 88 10531436
2003 Expression of olfactory-type cyclic nucleotide-gated channel (CNGA2) in vascular tissues. Histochemistry and cell biology 25 14618336
2014 Anxiety- and depressive-like behaviors in olfactory deficient Cnga2 knockout mice. Behavioural brain research 24 25192635
2013 Hysteresis of ligand binding in CNGA2 ion channels. Nature communications 24 24287615
2014 The first mutation in CNGA2 in two brothers with anosmia. Clinical genetics 20 25156905
2011 Retinoic acid receptor and CNGA2 channel signaling are part of a regulatory feedback loop controlling axonal convergence and survival of olfactory sensory neurons. FASEB journal : official publication of the Federation of American Societies for Experimental Biology 20 22009938
2008 CNGA2 channels mediate adenosine-induced Ca2+ influx in vascular endothelial cells. Arteriosclerosis, thrombosis, and vascular biology 18 18292397
2017 Isolated Congenital Anosmia and CNGA2 Mutation. Scientific reports 17 28572688
2009 CNGA2 contributes to ATP-induced noncapacitative Ca2+ influx in vascular endothelial cells. Journal of vascular research 13 19729961
2018 Genome Editing Reveals Idiosyncrasy of CNGA2 Ion Channel-Directed Antibody Immunoreactivity Toward Oxytocin. Frontiers in cell and developmental biology 10 30294598
2006 A single P-loop glutamate point mutation to either lysine or arginine switches the cation-anion selectivity of the CNGA2 channel. The Journal of general physiology 7 16533895
2005 Mutation of the pore glutamate affects both cytoplasmic and external dequalinium block in the rat olfactory CNGA2 channel. European biophysics journal : EBJ 0 15928936

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