Characterization of different intermediate states in myoglobin induced by polyethylene glycol: A process of spontaneous molecular self-organization foresees the energy landscape theory via in vitro and in silico approaches

Abstract

Practically proteins perform their functions exposed to various molecules (macro/micro) of different shapes, sizes, and high concentrations. In such conditions, proteins fold through various intermediate states to execute their type of functions. There are various in vitro studies that showed that proteins yield intermediate states (either pre-molten globule, PMG or molten globules, MG) in changing environments (pH, temperature, and co-solute). Here, we investigate that myoglobin (Mb) yields two intermediate states in the presence of polyethylene glycol, PEG (4 kDa molecular weight) at two different concentrations. These intermediates were characterized by various spectroscopic techniques, further; we demonstrated that these changes in the structure of the protein were due to soft interactions which were confirmed by isothermal titration calorimetric and computational studies. Besides, in silico (molecular dynamic simulations) studies were exploited to know the atomic-level details of the protein which are useful to comprehend the functional characteristics of the bio-molecule with structural change and to study atomic motions and inter-atomic interactions in the bio-molecular systems. This is the first time that two intermediates (MG and PMG state) in the protein (Mb) at two different concentrations in the presence of solo size of PEG are yielded. This study shows folding of a protein does not follow a singular and specific pathway but occurs through routes down a folding funnel more like rain flowing down a funnel, hence foresees the energy landscape theory. Moreover, the study provides the significance of crowding concentrations in the cellular organism.