Pharmacological Chaperone-mediated in Vivo Folding and Stabilization of the P23H-opsin Mutant Associated with Autosomal Dominant Retinitis Pigmentosa

Abstract

Protein conformational disorders, which include certain types of retinitis pigmentosa, are a set of inherited human diseases in which mutant proteins are misfolded and often aggregated. Many opsin mutants associated with retinitis pigmentosa, the most common being P23H, are misfolded and retained within the cell. Here, we describe a pharmacological chaperone, 11-cis-7-ring retinal, that quantitatively induces the in vivo folding of P23H-opsin. The rescued protein forms pigment, acquires mature glycosylation, and is transported to the cell surface. Additionally, we determined the temperature stability of the rescued protein as well as the reactivity of the retinal-opsin Schiff base to hydroxylamine. Our study unveils novel properties of P23H-opsin and its interaction with the chromophore. These properties suggest that 11-cis-7-ring retinal may be a useful therapeutic agent for the rescue of P23H-opsin and the prevention of retinal degeneration.

A Naturally Occurring Mutation of the Opsin Gene (T4R) in Dogs Affects Glycosylation and Stability of the G Protein-coupled Receptor

“…57) from the structurally unstable mutants like T4R Rho described in this study or the previously mentioned RP Asp 190 Rho mutant (53). Interestingly, the most common RP mutant, P23H Rho, in addition to structural changes (14), is also less stable than the WT protein (15).…”

“…However, it is somewhat surprising that the mutation on the intradiscal surface of the protein affects the chromophore-binding site and ultimately the cytoplasmic surface. We note that the P23H mutation on the intradiscal surface produces a hydrophilic channel in the interior of the protein that could accommodate water molecules and allow the hydrolysis of the covalently bound chromophore (14). Also, in the case of T4R, the chromophore appears to be destabilized by mutation in this general region.…”

“…The type of inheritance implies a strategy for potential intervention. For example, constitutive activity of K296E and K296M opsin mutants can be silenced by the addition of retinylamine analog inhibitors (13), whereas the misfolded protein for the P23H opsin mutant can be stabilized by retinoids, at least in a heterologous expression system (14,15). The disease-causing mutation T4K in opsin has been identified, but the molecular mechanism of the pathology caused by this mutant has not been elucidated (16).…”

Unfolding the therapeutic potential of chemical chaperones for age-related macular degeneration

“…Recently, Kaushal and colleagues demonstrated that the pharmacological molecule 11-cis-7-ring retinal, the inverse agonist to opsin, rescues the P23H mutant. They found that pharmacological chaperone therapy enabled the mutant protein to form pigment, acquire mature glycosylation, and localize to the cell surface [54]. Noorwez et al then showed that 9-and 11-cis-retinals could also act as pharmacological chaperones for P23H rhodopsin mutants expressed in HEK-293 cells.…”

“…Although, there is no clear target for chaperone treatment in AMD, increasing the expression of native molecular chaperones would likely help the cells respond to the stressed environment of the aging AMD macula. Moreover, chemical chaperones that help the RPE handle the accumulation of drusen components and lipofuscin or help photoreceptors prevent opsin aggregation may ameliorate ER-stress and stem AMD progression [54]. Less specifically, chemical chaperones with general protein folding interactions could help the AMD eye accommodate the range of stresses imposed on it.…”