The Chaperone‐like Activity and Structure of Mutant H119G of Rat Lens αB‐crystallin: A Study of Divalent Metal Ion Binding Site

Abstract

AbstractThe molecular chaperone αB‐crystallin, the major player in maintaining the transparency of the eye lens, preventing the aggregation of stress‐damaged and aging lens proteins from aggregation. In nonlenticular cells, it is involved in various neurological diseases, diabetes, and cancer. The role of some metal ions in the αB‐crystallin biology has been reported. Theoretical calculations have proposed that the coordination sites involving His101, His119, Lys121, His18 and Glu99 of human αB‐crystallin were the binding sites for divalent metal ions. Our previous mutagenesis study suggested that His18 rat lens αB‐crystallin is a crucial binding site for Cu(II) and Zn(II) in terms of chaperone‐like activity and structure. In this study mutant H119G of rat lens αB‐crystalin was cloned and expressed to investigate whether His119 is the coordination binding site. Copper and zinc at 1 mM concentration significantly increase the chaperone‐like activity in wild type αB‐crystalin, whereas zinc, copper and magnesium at 1 mM reduced the activity of H119G significantly. The results from chaperone‐like activity, ANS fluorescence measurement and Far‐and Near‐UV CD studies suggest that the replacement of His119 with Glycine resulted in a conformational and minor environmental changes that decrease chaperone‐like activity in the presence of divalent ions suggested that His119 was a crucial binding site for Cu(II) and Zn(II), which was similar to our previous study results of His18. Both results together suggest that His18 and His119 coordinates each other for the binding site of Cu(II) and Zn(II) in terms of improving the chaperone‐like activity and stability of crystallin/metal ion complex.