A novel GCAP1(N104K) mutation in EF-hand 3 (EF3) linked to autosomal dominant cone dystrophy

Abstract

The GUCA1A gene encodes a guanylate cyclase-activating protein (GCAP1) that is involved in regulation of phototransduction in the vertebrate retina. We discovered a novel C312A transversion in exon 2 of the human GUCA1A gene, replacing Asn-104 (N104) in GCAP1 with Lys (K), in two affected members of a family with dominant cone dystrophy. The mutation N104K is located in the third EF hand motif (EF3) shown previously to be instrumental in converting Ca2+-free GCAP1 to a GC inhibitor in the Ca2+-bound form. In one patient, rod ERGs were fairly stable over a 12-year-period whereas 30 Hz flicker ERG and single-flash cone ERGs declined. In both patients, double flash ERGs showed that rod recovery from an intense test flash was significantly delayed. The EC50 for GC stimulation shifted from ~250 nM in wild-type GCAP1 to ~800 nM in the GCAP1(N104K) mutant suggesting inability of the mutant to assume an inactive form under physiological conditions. The replacement of N104 by K in GCAP1 is the first naturally occurring mutation identified in the EF3 loop. The rod recovery delays observed in double-flash ERG of affected patients suggest a novel dominant-negative effect that slows GC stimulation.

Mutations in theGUCA1Agene involved in hereditary cone dystrophies impair calcium-mediated regulation of guanylate cyclase

“…Incomplete suppression of GC activity at high Ca 2+ concentration was also observed with other GCAP1 mutants (p.Tyr99Cys, p.Asn104Lys, p.Ile143AsnThr, p.Leu151Phe, and p.Glu155Gly, Dizhoor, et al, 1998;Sokal, et al, 1998;Jiang, et al, 2008;Nishiguchi, et al, 2004;Sokal, et al, 2005; pointing to the importance of an exactly balanced cGMP synthesis for undisturbed vision.…”

“…So far, only seven putative pathogenic mutations in the GUCA1A gene have been reported in patients with adCD, adCRD or adMD: p.Pro50Leu, p.Tyr99Cys, p.Asn104Lys, p.Thr114Ile, p.Ile143delinsAsnThr, p.Leu151Phe, and p.Glu155Gly (Dizhoor, et al, 1998;Downes, et al, 2001;Jiang, et al, 2005;Michaelides, et al, 2005;Nishiguchi, et al, 2004;Sokal, et al, 2005;Jiang et al, 2008. Here we report the identification of three novel and one previously published GUCA1A gene mutations in patients with adCD and adCRD.…”

Gucy2d- Or Guca1a-Related Autosomal Dominant Cone–rod Dystrophy

“…GUCA1A (GCAP1) and GUCA1B (GCAP2), located on chromosome 6p21.1, are both required for normal phototransduction. 10,[27][28][29][30][31] They are expressed in both photoreceptor types, but GCAP1 is predominantly present in cones, and GCAP2 is more abundant in rods. 32 GU-CA1C (GCAP3) was discovered in human retina and is exclusively expressed in cones; however, no mutations in GUCA1C have been associated with retinal disease.…”

Rod Photoreceptor Temporal Properties in Retinal Degenerative Diseases

“…Furthermore, rods that survived transient light damage in albino rat exhibited earlier-than-normal recovery (Wen 2008; Wen and Kraft 2008). Contrary to shortened rod recovery in RP, prolonged rod photoresponse recovery was observed in a type of cone dystrophy associated with GCAP1 mutations (Jiang et al 2008). In this study, we found that CRD caused by ABCA4 mutations ( T sat = 523 and 499 ms) is not associated with either shortened or elongated rod photoresponse recovery.…”