The P23H
opsin mutation is the most common cause of autosomal dominant
retinitis pigmentosa. Even though the pathobiology of the resulting
retinal degeneration has been characterized in several animal models, its complex molecular mechanism is not well understood. Here, we expressed P23H bovine
rod opsin in the nervous system of Caenorhabditis elegans. Expression was low due to enhanced protein degradation. The mutant
opsin was glycosylated, but the
polysaccharide size differed from that of the normal
protein. Although P23H
opsin aggregated in the nervous system of C. elegans, the pharmacological chaperone
9-cis-retinal stabilized it during biogenesis, producing a variant of
rhodopsin called P23H
isorhodopsin. In vitro, P23H
isorhodopsin folded correctly, formed the appropriate
disulfide bond, could be photoactivated but with reduced sensitivity, and underwent Meta II decay at a rate similar to wild type
isorhodopsin. In worm neurons, P23H
isorhodopsin initiated phototransduction by coupling with the endogenous Gi/o signaling cascade that induced loss of locomotion. Using pharmacological interventions affecting
protein synthesis and degradation, we showed that the chromophore could be incorporated either during or after
mutant protein translation. However, regeneration of P23H
isorhodopsin with chromophore was significantly slower than that of wild type
isorhodopsin. This effect, combined with the inherent instability of P23H
rhodopsin, could lead to the structural cellular changes and photoreceptor death found in autosomal dominant
retinitis pigmentosa. These results also suggest that slow regeneration of P23H
rhodopsin could prevent endogenous chromophore-mediated stabilization of
rhodopsin in the retina.