H101G Mutation in Rat Lens αB-Crystallin Alters Chaperone Activity and Divalent Metal Ion Binding

The molecular chaperone function of αB-crystallins is heavily involved in maintaining lens transparency and the development of cataracts.The aim of the study was to investigate whether divalent metal ion binding improves the stability and αB-crystallin chaperone activity.In this study, we have developed an H101G αB-crystallin mutant and compared the surface hydrophobicity, chaperone activity, and secondary and tertiary structure with the wild type in the presence and absence of metal ions.Substitution of His101 with glycine resulted in structural and functional changes. Spectral analysis and chaperone-like activity assays showed that substitution of glycine resulted in a higher percentage of random coils, increased hydrophobicity, and 22±2% higher chaperone-like activity. Whereas in the presence of the Cu2+ ion, H101G exhibited 32±1% less chaperone-like activity compared to the wild type.Cu2+ has been reported to enhance the chaperone-like activity of lens α-crystallin. Our results indicate that H101 is the predominant Cu2+ binding site, and the mutation resulted in a partial unfolding that impaired the binding of Cu2+ to H101 residue. In conclusion, this study further helps to understand the important binding site for Cu2+ to αB-crystallin.