Effect of Methylglyoxal Modification of Human alpha-Crystallin on the Structure, Stability and Chaperone Function

Abstract

alpha-Crystallin functions as a molecular chaperone and maintains transparency of eye lens by protecting other lens-proteins. Non-enzymatic glycation of alpha-crystallin by methylglyoxal, plays a crucial role on its chaperone function and structural stability. Our studies showed that methylglyoxal modification even in lower concentration caused significant decrease in chaperone function of alpha-crystallin as reflected both in thermal aggregation assay and enzyme refolding assay. Thermal denaturation studies showed drastic reduction of denaturation temperature with increase in the degree of modification. Thermodynamic stability studies by urea denaturation assay reflected a decrease of transition midpoint. Quantitatively we found that Delta GA degrees of native alpha-crystallin decreased from 21.6 kJ/mol to 10.4 kJ/mol due to 72 h modification by 10 mM methylglyoxal. The surface hydrophobicity of alpha-crystallin after MG modification, was found to be decreased. Circular dichroism spectroscopy revealed conversion of beta-sheet structure to random coil structure. Significant cross-linking was also observed due to methylglyoxal modification of human alpha-crystallin.