Influence of Calcium binding on the mechanical stability of M-Crystallin

Proteins that bind metal ions as a part of their normal physiological function may account for as many as 40% of all proteins, understanding the relationships between structures of proteins and their ability to bind metal ions is an important aspect of protein science. Ca2+ binding has wide variety of biological roles spanning from triggering muscle contraction to regulating neurotransmitters and hormones. These effects are mediated by binding of Ca2+ to regulatory proteins such as calmodulin, troponin C etc.

M-Crystallin is one such calcium binding protein from a Mesophilic archea showing structural homology to mammalian eye lens crystallins.Studying the archeal homologue helps to understand the evolutionary relationship of lens crystallins and their calcium binding properties. Bulk studies like Fluorescence and Circular Dichroism spectroscopy revealed that there was no significant change in their conformation upon calcium unbound and bound form. Whereas, from our data of single molecule force spectroscopy, we could see binding of calcium enhances the stability in terms of unfolding force from 91 pN in calcium unbound form to 125pN in bound form. Moreover, varying the pulling speed and Monte Carlo simulations helped us to understand the dependence of unfolding force to pulling speed.