Structural Insights into IbpA–IbpB Interactions to Predict Their Roles in Heat Shock Response

Abstract

Cells respond to stress conditions. As a result of stress, most genes are deactivated, while a few are activated with antistress response. The latter involves a variety of molecules including molecular chaperones or heat shock proteins (Shps) whose levels get increased in stressed conditions, particularly at elevated temperatures. Heat shock proteins help the other cellular proteins to achieve their native states, i.e. correct folding or functional conformations. Thus, heat shock proteins play a major role in protein homeostasis network of the cell. Small heat shock proteins (sHsps) are one of the families of molecular chaperones that prevent the irreversible aggregation and assist in the refolding of denatured proteins. Two members of the sHsp family, IbpA and IbpB, are present in Escherichia coli. The IbpA and IbpB proteins are 48 % identical at the amino acid sequence level and have the characteristic α-crystalline domain. It is known that the cooperation between IbpA and IbpB is crucial for their chaperone activity in heat stressed condition. So far, the molecular mechanisms of the stress response of the IbpA/IbpB protein system have not been well understood. In the present work, an attempt has been made to identify the amino acid residues of the IbpA and IbpB proteins, which are found to be involved in protein–protein interactions. The interactions between IbpA and IbpB are studied with and without the presence of substrate Lactate Dehydrogenase (LDH) at cold shock, physiological and heat shock temperatures to observe the changes in the pattern of interaction. This study is the first report to elucidate the mechanism of interactions between the proteins.