Competition for hydrogen bond formation in the helix-coil transition and protein folding

TL;DR

This paper analytically investigates the helix-coil transition in biopolymers, revealing a reentrant transition caused by competition between polymer-polymer and polymer-water hydrogen bonds, influenced by external conditions.

Contribution

It introduces a modified Generalized Model of Polypeptide Chains to explain reentrant transitions and the effects of external factors on hydrogen bonding in biopolymers.

Findings

Reentrant helix-coil transition due to hydrogen bond competition

External factors like pressure and force influence transition behavior

Agreement with recent experimental observations

Abstract

The problem of the helix-coil transition of biopolymers in explicit solvents, like water, with the ability for hydrogen bonding with solvent is addressed analytically using a suitably modified version of the Generalized Model of Polypeptide Chains. Besides the regular helix-coil transition, an additional coil-helix or reentrant transition is also found at lower temperatures. The reentrant transition arises due to competition between polymer-polymer and polymer-water hydrogen bonds. The balance between the two types of hydrogen bonding can be shifted to either direction through changes not only in temperature, but also by pressure, mechanical force, osmotic stress or other external influences. Both polypeptides and polynucleotides are considered within a unified formalism. Our approach provides an explanation of the experimental difficulty of observing the reentrant transition with pressure; and underscores the advantage of pulling experiments for studies of DNA. Results are discussed and compared with those reported in a number of recent publications with which a significant level of agreement is obtained.