Structure and function in rhodopsin: Mass spectrometric identification of the abnormal intradiscal disulfide bond in misfolded retinitis pigmentosa mutants

Retinitis pigmentosa (RP) point mutations in both the intradiscal (ID) and transmembrane domains of rhodopsin cause partial or complete misfolding of rhodopsin. resulting in loss of Il-cis-retinal binding. Previous work has s hown that misfolding is caused by the formation of a disulfide bond in the ID domain different from the native Cys-110-Cys-187 disulfide bond in nativ e rhodopsin. Here we report on direct identification of the abnormal disulf ide bond in misfolded RP mutants in the transmembrane domain by mass spectr ometric analysis. This disulfide bond is between Cys-185 and Cys-187. the s ame as previously identified in misfolded RP mutations in the ID domain. Th e strategy described here should be generally applicable to identification of disulfide bonds in other integral membrane proteins.