Wild-type opsin does not aggregate with a misfolded opsin mutant

Abstract

Rhodopsin is the light receptor in photoreceptor cells that plays a central role in phototransduction and photoreceptor cell health. Mutations in rhodopsin are the leading cause of autosomal dominant retinitis pigmentosa (adRP), a retinal degenerative disease. A majority of mutations in rhodopsin cause misfolding and aggregation of the apoprotein opsin. The pathogenesis of adRP caused by misfolded opsin is unclear. It has been proposed that physical interactions between wild-type opsin and misfolded opsin mutants may underlie the autosomal dominant phenotype. To test whether or not wild-type opsin can form a complex with misfolded opsin mutants, we examined the interactions between wild-type opsin and opsin with a G188R mutation, a clinically identified mutation causing adRP. Förster resonance energy transfer (FRET) was utilized to monitor the interactions between fluorescently tagged opsins expressed in live cells. The FRET assay employed was able to discriminate between properly folded opsin oligomers and misfolded opsin aggregates. Wild-type opsin predominantly formed oligomers and only a minor population formed aggregates. Conversely, the G188R opsin mutant predominantly formed aggregates. When wild-type opsin and G188R opsin were coexpressed in cells, properly folded wild-type opsin did not aggregate with G188R opsin and was trafficked normally to the plasma membrane. Thus, the autosomal dominant phenotype in adRP caused by misfolded opsin mutants is not predicted to arise from physical interactions between wild-type opsin and misfolded opsin mutants.