Impaired Association of Retinal Degeneration-3 with Guanylate Cyclase-1 and Guanylate Cyclase-activating Protein-1 Leads to Leber Congenital Amaurosis-1

Abstract

Background: Defects in the function of guanylate cyclase 1 (GC1) cause Leber congenital amaurosis (LCA) type 1. Results: GC1, GCAP1, and RD3 form a complex in the endoplasmic reticulum that targets GC1 to outer segments. Conclusion: A subset of LCA1 is caused by impaired formation of the RD3-GC1-GCAP1 complex. Significance: Understanding the molecular interaction of RD3 with GC1 and GCAP1 has potential therapeutic benefits for LCA1.

Functional Study and Mapping Sites for Interaction with the Target Enzyme in Retinal Degeneration 3 (RD3) Protein

“…Ϫ/Ϫ Mice-The lack of RD3, which diminishes the content of RetGCs in the outer segments (3,5), strongly reduced the overall activity of the cyclase detectable in young rd3/rd3 mice (Fig. 2).…”

“…1) and (ii) RD3 (retinal degeneration 3) protein (2), which inhibits RetGC and is required for normal accumulation of the cyclase in rod and cone outer segments (3)(4)(5). Although the lack of GCAPs alters the kinetics and light sensitivity of photoresponse without destroying photoreceptors (6,7), the RD3 deficiency causes retinal degeneration in rd3/rd3 mouse strain and in human patients affected by congenital blindness (2).…”

“…Although the details of the mechanism through which GCAPs bind and regulate RetGC have gradually become understood, the function of RD3 as a negative regulator of the photoreceptor cyclase, as well as its physiological role, remains less clear. Adding even more importance to that subject, some mutations in RetGC1 that cause Leber congenital amaurosis, a severe from of an earlyonset blindness, interfere with the cyclase binding of GCAPs and RD3 altogether (4,5,8,9). We hypothesized that blocking the cyclase activity by high-affinity RD3 binding could prevent premature activation of RetGC in the inner segment of the photoreceptor, before it reaches its proper destination in the outer segment (4).…”

“…Although the lack of GCAPs alters the kinetics and light sensitivity of photoresponse without destroying photoreceptors (6,7), the RD3 deficiency causes retinal degeneration in rd3/rd3 mouse strain and in human patients affected by congenital blindness (2). Photoreceptors lacking RD3 fail to produce normal levels of RetGC1 and RetGC2 isozymes and to accumulate them in the outer segment, indicating that binding of RD3 by the cyclase provides proper stability and/or trafficking of the cyclase (3,5). We previously reported that RD3 is a very potent high-affinity inhibitor of the cyclase catalytic activity as well as its activation by GCAPs in vitro (4).…”

The R838S Mutation in Retinal Guanylyl Cyclase 1 (RetGC1) Alters Calcium Sensitivity of cGMP Synthesis in the Retina and Causes Blindness in Transgenic Mice

“…Two RetGC isozymes expressed in photoreceptors, RetGC1 and RetGC2 (6 -8), bind calcium-sensor proteins, GCAPs (7)(8)(9)(10)(11)(12), which decelerate the cyclase activity at high intracellular calcium concentrations in the dark and accelerate it in the light, when the influx of calcium through the cGMP-gated channels is shut off (13)(14)(15)(16)(17)(18)(19). RetGC also binds retinal degeneration 3 (RD3) protein (20 -21), which prevents cyclase activation by GCAPs (22)(23) and promotes accumulation of RetGC1 in the outer segments (21,24,25). RetGC1 (human gene GUCY2D) accounts for most of the cGMP synthesis in mammalian photoreceptors (26,27), therefore mutations in RetGC1 that disable the cyclase activity (28 -33) cause recessive blindness at birth, Leber congenital amaurosis type 1 (LCA1) (33), mostly a non-degenerative or partially degenerative (31,32) loss-of-function hereditary retinal disease.…”