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

Background: The molecular chaperone function of αB-crystallins is heavily involved in maintaining lens transparency and the development of cataracts. Objectives: The aim of the study was to investigate whether divalent metal ion binding improves the stability and αB-crystallin chaperone activity. Methods: 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. Results: 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. Conclusion: 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.