Molecular and functional characterization of the retinitis pigmentosa G90V mutation in a conformationally stabilized rhodopsin background

Mutations in the photoreceptor protein rhodopsin can lead to visual dysfunction and retinal degeneration. The G90^2.57V mutation, in the second transmembrane helix, causes a retinitis pigmentosa phenotype. A conformationally stabilized wild-type rhodopsin bearing an engineered disulfide bond (N2C/D282C) was developed for structural studies of disease-associated mutations. However, this extra disulfide bond may mask the native conformational features of rhodopsin mutants. Here, we investigate the structural and functional consequences of the G90^2.57V mutation in this stabilized context. The G90^2.57V substitution disrupts interactions within the retinal binding pocket, particularly with E113^3.28 in transmembrane helix 3, which stabilizes the Schiff base linkage to 11-cis-retinal. Our results demonstrate that the N2C/D282C disulfide bond counteracts the destabilizing effects of the G90^2.57V mutation by enhancing thermal and chemical stability of the pigment and improving chromophore regeneration. These findings underscore the importance helix and loop interactions in rhodopsin function and highlight the potential of structural modifications to rescue impaired mutants. Furthermore, our work provides novel insights into the effect of engineered disulfide bonds on the structure and dynamics of rhodopsin mutants associated with retinal diseases and allows one to dissect the effects of the disulfide bond from those of the rhodopsin mutation alone.