Coil-helix transition of polypeptide at water-lipid interface

TL;DR

This paper provides an exact solution to a microscopic statistical mechanical model describing the coil-helix transition of polypeptides at water-lipid interfaces, elucidating the nature of the transition and related thermodynamic properties.

Contribution

It introduces a novel exactly solvable model for polypeptide conformational change at interfaces, capturing various transition types and detailed thermodynamic behavior.

Findings

The model predicts crossover, discontinuous, or continuous transitions depending on parameters.

Explicit calculations of helicity, entropy, and heat capacity are provided.

The transition mechanism is characterized by the behavior of helicity as an order parameter.

Abstract

We present the exact solution of a microscopic statistical mechanical model for the transformation of a long polypeptide between an unstructured coil conformation and an $\alpha$-helix conformation. The polypeptide is assumed to be adsorbed to the interface between a polar and a non-polar environment such as realized by water and the lipid bilayer of a membrane. The interfacial coil-helix transformation is the first stage in the folding process of helical membrane proteins. Depending on the values of model parameters, the conformation changes as a crossover, a discontinuous transition, or a continuous transition with helicity in the role of order parameter. Our model is constructed as a system of statistically interacting quasiparticles that are activated from the helix pseudo-vacuum. The particles represent links between adjacent residues in coil conformation that form a self-avoiding random walk in two dimensions. Explicit results are presented for helicity, entropy, heat capacity, and the average numbers and sizes of both coil and helix segments.