Macromolecular Crowding Enhances the Efficiency of the Chemical Chaperone, Betaine in Inhibiting Protein Aggregation

Abstract

Presently, protein aggregation is of intense medical interest since the deposition of protein aggregates in vivo is related to the pathogenesis of many diseases. Interestingly, chemical chaperones accumulated by organisms during stress have been shown to assist in proper protein folding thereby preventing aggregation. However, most of these studies have been performed under dilute conditions as compared to the crowded intracellular environment where proteins perform their function. Indeed, the cell interior is known to be crowded due to the presence of soluble and insoluble macromolecules, which occupy ~40% of the total cellular volume. The degree of volume occupancy by these macromolecules is expected to have significant effect on protein aggregation. It is, thus, important to understand the protective role of chemical chaperones against protein aggregation under conditions mimicking crowded intracellular environment to have a real insight of the in vivo scenario. In this spirit, we have investigated the aggregation behavior of carbonic anhydrase in the presence of betaine, a chemical chaperone under crowded conditions using various spectroscopic techniques and electron microscopy. The results suggest a dramatic increase in the efficiency of betaine in preventing protein aggregation under crowded conditions which is speculated to result from the additive effect of preferential hydration by betaine and excluded volume effect encountered under crowded conditions. It is concluded that chemical chaperones are much more efficient than expected in maintaining protein homeostasis under crowded in vivo conditions. This work is supported by grant from DST, India. Authors acknowledge CSIR, India for providing research fellowship.