Conformational changes of bovine lens crystallins in a photodynamic system.

Abstract

Abstract— Conformational changes of bovine lens crystallins in a photodynamic system generating singlet oxygen, have been investigated. The formation of intersubunit crosslinks was observed in all three classes (α‐, β and γ‐) of crystallins by irradiation in the presence of the photosensitizer methylene blue. Near‐UV circular dichroism (CD) spectra of the crystallins were significantly altered by irradiation under these conditions, indicating changes in tertiary structure but the far‐UV CD remained unchanged suggesting that the secondary structure ((β‐sheet conformation) remains unchanged. Significant changes in the absorption and fluorescence spectra were also observed. Measurement of total sulfhydryl content showed a decrease of 27%, 50% and 37% for α‐, β‐ and γ‐crystallins respectively, after irradiation. Fluorescence lifetime measurements of N‐iodoacetyl‐N'‐(5‐sulfo‐l‐naphthyl)ethylenediamine‐labeled crystallins showed a significant decrease of the lifetime of the major decay components of the label bound to sulfhydryl groups of α‐ and γ‐crystallins, but showed no change in the microenvironment of the sulfhydryl groups of β‐crystallin. The results are consistent with the microenvironments of the tryptophan and sulfhydryl groups predicted from sequence studies.