Structural changes in barley protein LTP1 isoforms at air-water interfaces

TL;DR

This study uses a coarse-grained model to analyze how barley proteins LTP1 and LTP1b change shape at air-water interfaces, revealing their role in foam stability in beer.

Contribution

It introduces a hydropathy-based model validated by all-atom simulations to investigate protein conformational changes at interfaces, focusing on foam formation.

Findings

Proteins flatten and form dense films at the interface.

Flattening degree varies with protein type and glycation.

Disulfide bond number influences protein geometry.

Abstract

We use a coarse-grained model to study the conformational changes in two barley proteins, LTP1 and its ligand adduct isoform LTP1b, that result from their adsorption to the air-water interface. The model introduces the interface through hydropathy indices. We justify the model by all-atom simulations. The choice of the proteins is motivated by making attempts to understand formation and stability of foam in beer. We demonstrate that both proteins flatten out at the interface and can make a continuous stabilizing and denser film. We show that the degree of the flattening depends on the protein -- the layers of LTP1b should be denser than those of LTP1 -- and on the presence of glycation. It also depends on the number ($\le 4$) of the disulfide bonds in the proteins. The geometry of the proteins is sensitive to the specificity of the absent bonds. We provide estimates of the volume of cavities of the proteins when away from the interface.