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PLoS One. 2015 Sep 25;10(9):e0138943. doi: 10.1371/journal.pone.0138943. eCollection 2015.

Canine CNGA3 Gene Mutations Provide Novel Insights into Human Achromatopsia-Associated Channelopathies and Treatment.

Author information

1
Department of Biology, College of Science and Technology, Temple University, Philadelphia, Pennsylvania, United States of America.
2
Department of Clinical Studies-Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
3
Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania, United States of America.
4
Veterinary Vision, Penrith, Cumbria, CA11 9FJ, United Kingdom.

Abstract

Cyclic nucleotide-gated (CNG) ion channels are key mediators underlying signal transduction in retinal and olfactory receptors. Genetic defects in CNGA3 and CNGB3, encoding two structurally related subunits of cone CNG channels, lead to achromatopsia (ACHM). ACHM is a congenital, autosomal recessive retinal disorder that manifests by cone photoreceptor dysfunction, severely reduced visual acuity, impaired or complete color blindness and photophobia. Here, we report the first canine models for CNGA3-associated channelopathy caused by R424W or V644del mutations in the canine CNGA3 ortholog that accurately mimic the clinical and molecular features of human CNGA3-associated ACHM. These two spontaneous mutations exposed CNGA3 residues essential for the preservation of channel function and biogenesis. The CNGA3-R424W results in complete loss of cone function in vivo and channel activity confirmed by in vitro electrophysiology. Structural modeling and molecular dynamics (MD) simulations revealed R424-E306 salt bridge formation and its disruption with the R424W mutant. Reversal of charges in a CNGA3-R424E-E306R double mutant channel rescued cGMP-activated currents uncovering new insights into channel gating. The CNGA3-V644del affects the C-terminal leucine zipper (CLZ) domain destabilizing intersubunit interactions of the coiled-coil complex in the MD simulations; the in vitro experiments showed incompetent trimeric CNGA3 subunit assembly consistent with abnormal biogenesis of in vivo channels. These newly characterized large animal models not only provide a valuable system for studying cone-specific CNG channel function in health and disease, but also represent prime candidates for proof-of-concept studies of CNGA3 gene replacement therapy for ACHM patients.

PMID:
26407004
PMCID:
PMC4583268
DOI:
10.1371/journal.pone.0138943
[Indexed for MEDLINE]
Free PMC Article

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