Glycation induced conformational transitions in cystatin proceed to form biotoxic aggregates: A multidimensional analysis.

Hyperglycaemic conditions facilitate the glycation of serum proteins which may have predisposition to aggregation and thus lead to complications. The current study investigates the glycation induced structural and functional modifications of chickpea cystatin (CPC) as well as biological toxicity of the modified protein forms, using CPC-glucose as a model system. Several structural intermediates were formed during the incubation of CPC with glucose (day 4, 8, 12, & 16) as revealed by circular dichroism (CD), altered intrinsic fluorescence, and high ANS binding. Further incubation of CPC with glucose (day 21) formed abundant β structures as revealed by Fourier transform infrared spectroscopy and CD analysis which may be due to the aggregation of protein. High thioflavin T fluorescence intensity and increased Congo red absorbance together with enhanced turbidity and Rayleigh scattering by this modified form confirmed the aggregation. Electron microscopy finally provided the valid physical authentication about the presence of aggregate structures. Functional inactivation of glucose incubated CPC was also observed with time. Single cell electrophoresis of lymphocytes and plasmid nicking assays in the presence of modified CPC showed the DNA damage which confirmed its biological toxicity. Hence, our study suggests that glycation of CPC not only leads to structural and functional alterations in proteins but also to biotoxic AGEs and aggregates.