Unfolding of Dynamical Events in the Early Stage of Insulin Dimer Dissociation

Mondal, S and Mukherjee, S and Acharya, S and Bagchi, B (2021) Unfolding of Dynamical Events in the Early Stage of Insulin Dimer Dissociation. In: Journal of Physical Chemistry B, 125 (29). pp. 7958-7966.

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Abstract

The dissociation of an insulin dimer is an important biochemical event that could also serve as a prototype of dissociations in similar biomolecular assemblies. We use a recently developed multidimensional free energy landscape for insulin dimer dissociation to unearth the microscopic and mechanistic aspects of the initial stages of the process that could hold the key to understanding the stability and the rate. The following sequence of events occurs in the initial stages: (i) The backbone hydrogen bonds break partially at the antiparallel β-sheet junction, (ii) the two α-helices (chain B) move away from each other while several residues (chain A) move closer, and (iii) a flow of adjacent water molecules occurs into the junction region. Interestingly, the intermonomeric center-to-center distance does not increase, but the number of native contacts exhibits a sharp decrease. Subsequent steps involve further disengagement of hydrophobic groups. This process is slow because of an entropic bottleneck created by the existence of the large configuration space available in the native state (NS), which is inhabited by low-frequency conformational fluctuations. We carry out a density-of-states analyses in the dimer NS to unearth distinctive features not present in the monomers. These low-frequency modes are also responsible for a large entropic stabilization of the NS. Hydrophobic disengagement in the early stage leads to the formation of a twisted intermediate state which itself is a metastable minimum (IS-1). The subsequent progress leads to another dimeric complex (IS-2), which is on the dissociative pathway and characterized by a further decrease in the native contacts. The dissociation process provides insights into the workings of a biomolecular assembly. ©

Item Type:	Journal Article
Publication:	Journal of Physical Chemistry B
Publisher:	American Chemical Society
Additional Information:	The copyright for this article belongs to American Chemical Society
Keywords:	Dimers; Free energy; Hydrogen bonds; Hydrophobicity; Insulin; Molecules, Configuration space; Conformational fluctuations; Density-of-states analysis; Dissociation process; Dissociative pathways; Entropic stabilization; Low-frequency modes; Multidimensional free energy, Dissociation
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	20 Nov 2021 11:31
Last Modified:	20 Nov 2021 11:31
URI:	http://eprints.iisc.ac.in/id/eprint/69849

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