Spectral and thermal properties of novel eye lens ζ-crystallin.

Eye lenses are exposed to thermal, solar radiations, dryness that enhances cataractogenesis. Some animal lenses contain novel proteins in bulk quantities. zeta-crystallin occurred in three ecologically divergent species, but it's physiological role not known. The truncated variant of zeta-crystallin causes hereditary cataract. Guinea pig zeta-crystallin is temperature-sensitive and rapidly aggregates at 41 degrees C. Camels adopted to survive above 50 degrees C, which raises an interesting question about how it retains lens proteins in the soluble state? Here, we have optimized expression and purification of recombinant camel zeta-crystallin. We have studied thermodynamic and spectroscopic properties using orthogonal techniques. Dynamic multimode spectroscopy results showed that camel zeta-crystallin unfolds via single transition with T-m value of 60.8 +/- 0.1 degrees C and van't Hoff enthalpy of 714.7 +/- 7.1 kJ/mol. Thermal-shift assay calculates T-m value of 62 degrees C at pH 7. Additionally, the conformational stability of zeta-crystallin increases with ionic-strength. The influence of pH on zeta-crystallin was evaluated where the protein was found to be stable in the pH range of 6-9, but its stability drastically decreases below pH 6. Our results also showed that quaternary structure of zeta-crystallin drastically changed as a result of lowering pH. This study provides significant understandings onto the conformational, thermodynamic and unfolding pathway of camel zeta-crystallin. (C) 2017 Elsevier B.V. All rights reserved.