Structure, Chaperone Activity, and Aggregation of Wild-Type and R12C Mutant αB-Crystallins in the Presence of Thermal Stress and Calcium Ion – Implications for Role of Calcium in Cataract Pathogenesis

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M. Ragerdi Kashani¹, R. Yousefi^1*, M. Akbarian¹, M. M. Alavianmehr², and Y. Ghasemi³

¹Shiraz University, Protein Chemistry Laboratory (PCL), Department of Biology, 71345 Shiraz, Iran; fax: + (98) 711-32280916; E-mail: ryousefi@shirazu.ac.ir

²Shiraz University of Technology, Department of Chemistry, Shiraz, Iran

³Department of Pharmaceutical Biotechnology and Pharmaceutical Sciences Research Center, School of Pharmacy, Shiraz University of Medical Sciences, Shiraz, Iran

^* To whom correspondence should be addressed.

Received August 9, 2015; Revision received September 19, 2015

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The current study was performed with the aim to evaluate the chaperoning ability, structural features, and aggregation propensity of wild-type and R12C mutant αB-crystallins (αB-Cry) under thermal stress and in the presence of calcium ion. The results of different spectroscopic analyses suggest that wild-type and mutant αB-Cry have dissimilar secondary and tertiary structures. Moreover, αB-Cry indicates slightly improved chaperone activity upon the R12C mutation. Thermal stress and calcium, respectively, enhance and reduce the extent of solvent-exposed hydrophobic surfaces accompanying formation of ordered and non-ordered aggregate entities in both proteins. Compared to the wild-type protein, the R12C mutant counterpart shows significant resistance against thermal and calcium-induced aggregation. In addition, in the presence of calcium, significant structural variation was accompanied by reduction in the solvent-exposed hydrophobic patches and attenuation of chaperone activity in both proteins. Additionally, gel mobility shift assay indicates the intrinsic propensity of R12C mutant αB-Cry for disulfide bridge-mediated protein dimerization. Overall, the results of this study are of high significance for understanding the molecular details of different factors that are involved in the pathomechanism of cataract disorders.

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KEY WORDS: αB-crystallin, R12C mutation, chaperone, thermal stress, aggregation

DOI: 10.1134/S0006297916020061

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