Photosensitized effects of Rose Bengal on structure and function of lens protein "alpha-crystallin"

The conformational changes of the bovine lens protein "alpha-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 x 10(-6) M] and Fourier transform-IR spectra of alpha-crystallin [5 mg mL(-1)] were significantly altered upon RB alpha-crystallin complex formation. RB was found to bind to alpha-crystallin in a molecular pocket characterized by a low polarity, with Trp most likely involved in this interaction. The binding constant (K(b)) has been estimated to be of the order of 2.5 (mg/mL)(-1). The intrinsic fluorescence of alpha-crystallin was quenched through both dynamic and static mechanisms. Light-induced photosensitized effects showed structural modifications in alpha-crystallin, including tertiary and secondary structure (an increase in unordered structure) alterations. Notwithstanding those photoinduced structural variations detected in alpha-crystallin when complexed with RB, the protein still retains its ability to play the role of chaperone for beta-crystallin.