Photosensitized Effects of Rose Bengal on Structure and Function of Lens Protein "Alpha-Crystallin"

The conformational changes of the bovine lens protein “α‐crystallin” have been investigated in the presence of the photosensitizer Rose Bengal (RB), in the dark as well as after visible light irradiation. Absorption and fluorescence emission spectra of RB [5 × 10−6 m] and Fourier transform‐IR spectra of α‐crystallin [5 mg mL−1] were significantly altered upon RB α‐crystallin complex formation. RB was found to bind to α‐crystallin in a molecular pocket characterized by a low polarity, with Trp most likely involved in this interaction. The binding constant (Kb) has been estimated to be of the order of 2.5 (mg/mL)−1. The intrinsic fluorescence of α‐crystallin was quenched through both dynamic and static mechanisms. Light‐induced photosensitized effects showed structural modifications in α‐crystallin, including tertiary and secondary structure (an increase in unordered structure) alterations. Notwithstanding those photoinduced structural variations detected in α‐crystallin when complexed with RB, the protein still retains its ability to play the role of chaperone for β‐crystallin.