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Neuronal Calcium Sensors in Health and Disease

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Front. Mol. Neurosci. | doi: 10.3389/fnmol.2018.00348

Photoreceptor Guanylate Cyclase (GUCY2D) mutations cause retinal dystrophies by severe malfunction of Ca2+-dependent cyclic GMP synthesis

 Hanna Wimberg1, Dorit Lev2, Keren Yosovich2,  Prasanthi Namburi3, Eyal Banin3,  Dror Sharon3 and  Karl-Wilhelm Koch1*
  • 1Neuroscience, University of Oldenburg, Germany
  • 2Sackler School of Medicine, Sackler Faculty of Medicine, Tel Aviv University, Israel
  • 3Hadassah-Hebrew University Medical Center, Israel

Over 100 mutations in GUCY2D that encodes the photoreceptor guanylate cyclase GC-E are known to cause two major diseases: autosomal recessive Leber congenital amaurosis (arLCA) or autosomal dominant cone-rod dystrophy (adCRD) with a poorly understood mechanism at the molecular level in most cases. Only few mutations were further characterized for their enzymatic and molecular properties. GC-E activity is under control of neuronal Ca2+-sensor proteins, which is often a possible route to dysfunction. We investigated five recently-identified GC-E mutants that have been reported in patients suffering from arLCA (1 large family) and adCRD/maculopathy (4 families). Microsatellite analysis revealed that one of the mutations, c.2538G>C (p.K846N), occurred de-novo. To better understand the mechanism by which mutations that are located in different GC-E domains develop different phenotypes, we investigated the molecular consequences of these mutations by expressing wildtype and mutant GC-E variants in HEK293 cells. Analyzing their general enzymatic behavior, their regulation by Ca2+ sensor proteins and retinal degeneration protein 3 (RD3) dimerization domain mutants (p.E841K and p.K846N) showed a shift in Ca2+-sensitive regulation by guanylate cyclase-activating proteins (GCAPs). Mutations in the cyclase catalytic domain led to a loss of enzyme function in the mutant p.P873R, but not in p.V902L. Instead, the p.V902L mutation increased the guanylate cyclase activity more than 20-fold showing a high GCAP independent activity and leading to a constitutively active mutant. This is the first mutation to be described affecting the GC-E catalytic core in a complete opposite way.

Keywords: GUCY2D mutation, Guanylate Cyclase, Leber Congenital Amaurosis, cone-rod dystrophy, RD3 protein, GCAP, guanylate cyclase activating protein

Received: 29 Jun 2018; Accepted: 06 Sep 2018.

Edited by:

Vsevolod V. Gurevich, Vanderbilt University, United States

Reviewed by:

Marie E. Burns, University of California, Davis, United States
Alecia K. Gross, University of Alabama at Birmingham, United States
Ching-Kang J. Chen, Baylor College of Medicine, United States
Maxim Sokolov, West Virginia University, United States  

Copyright: © 2018 Wimberg, Lev, Yosovich, Namburi, Banin, Sharon and Koch. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Karl-Wilhelm Koch, University of Oldenburg, Neuroscience, Oldenburg, 26129, Lower Saxony, Germany, karl.w.koch@uni-oldenburg.de