A G86R mutation in the calcium-sensor protein GCAP1 alters regulation of retinal guanylyl cyclase and causes dominant cone-rod degeneration.

Abstract

The guanylyl cyclase-activating protein, GCAP1, activates photoreceptor membrane guanylyl cyclase (RetGC) in the light, when free Ca2+ concentrations decline, and decelerates the cyclase in the dark, when Ca2+ concentrations rise. Here, we report a novel mutation, G86R, in the GCAP1 (GUCA1A) gene in a family with a dominant retinopathy. The G86R substitution in a "hinge" region connecting EF-hand domains 2 and 3 in GCAP1 strongly interfered with its Ca2+-dependent activator-to-inhibitor conformational transition. The G86R-GCAP1 variant activated RetGC at low Ca2+ concentrations with higher affinity than did the WT GCAP1, but failed to decelerate the cyclase at the Ca2+ concentrations characteristic of dark-adapted photoreceptors. Ca2+-dependent increase in Trp94 fluorescence, indicative of the GCAP1 transition to its RetGC inhibiting state, was suppressed and shifted to a higher Ca2+ range. Conformational changes in G86R GCAP1 detectable by isothermal titration calorimetry (ITC) also became less sensitive to Ca2+, and the dose dependence of the G86R GCAP1-RetGC1 complex inhibition by retinal degeneration 3 (RD3) protein was shifted toward higher than normal concentrations. Our results indicate that the flexibility of the hinge region between EF-hands 2 and 3 is required for placing GCAP1-regulated Ca2+ sensitivity of the cyclase within the physiological range of intracellular Ca2+ at the expense of reducing GCAP1 affinity for the target enzyme. The disease-linked mutation of the hinge Gly86, leading to abnormally high affinity for the target enzyme and reduced Ca2+ sensitivity of GCAP1, is predicted to abnormally elevate cGMP production and Ca2+ influx in photoreceptors in the dark.

• Authors: Igor V Peshenko, Artur V Cideciyan, Alexander Sumaroka, Elena V Olshevskaya, Alexander Scholten, Seher Abbas, Karl-Wilhelm Koch, Samuel G Jacobson, Alexander M Dizhoor
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 294 Issue 10 Pg. 3476-3488 (03 08 2019) ISSN: 1083-351X [Electronic] United States
• PMID: 30622141 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: © 2019 Peshenko et al.

Chemical References

• Guanylate Cyclase-Activating Proteins
• Guanylate Cyclase
• Calcium

Topics

• Calcium (metabolism)
• Cell Death (genetics)
• Cone-Rod Dystrophies (enzymology, genetics, metabolism, pathology)
• Guanylate Cyclase (metabolism)
• Guanylate Cyclase-Activating Proteins (chemistry, genetics, metabolism)
• Humans
• Models, Molecular
• Mutation
• Protein Conformation, alpha-Helical
• Retina (enzymology, pathology)
• Retinal Cone Photoreceptor Cells (pathology)
• Retinal Rod Photoreceptor Cells (pathology)