Structural perturbation and enhancement of the chaperone‐like activity of α‐crystallin by arginine hydrochloride

AbstractStructural perturbation of α‐crystallin is shown to enhance its molecular chaperone‐like activity in preventing aggregation of target proteins. We demonstrate that arginine, a biologically compatible molecule that is known to bind to the peptide backbone and negatively charged side‐chains, increases the chaperone‐like activity of calf eye lens α‐crystallin as well as recombinant human αA‐ and αB‐crystallins. Arginine‐induced increase in the chaperone activity is more pronounced for αB‐crystallin than for αA‐crystallin. Other guanidinium compounds such as aminoguanidine hydrochloride and guanidine hydrochloride also show a similar effect, but to different extents. A point mutation, R120G, in αB‐crystallin that is associated with desmin‐related myopathy, results in a significant loss of chaperone‐like activity. Arginine restores the activity of mutant protein to a considerable extent. We have investigated the effect of arginine on the structural changes of α‐crystallin by circular dichroism, fluorescence, and glycerol gradient sedimentation. Far‐UV CD spectra show no significant changes in secondary structure, whereas near‐UV CD spectra show subtle changes in the presence of arginine. Glycerol gradient sedimentation shows a significant decrease in the size of α‐crystallin oligomer in the presence of arginine. Increased exposure of hydrophobic surfaces of α‐crystallin, as monitored by pyrene‐solubilization and ANS‐fluorescence, is observed in the presence of arginine. These results show that arginine brings about subtle changes in the tertiary structure and significant changes in the quaternary structure of α‐crystallin and enhances its chaperone‐like activity significantly. This study should prove useful in designing strategies to improve chaperone function for therapeutic applications.