Small angle neutron scattering contrast variation reveals heterogeneities of interactions in protein gels

TL;DR

This study uses small angle neutron scattering contrast variation to reveal heterogeneities in protein gels, showing inhomogeneous deuteration and phase separation related to glutenin interactions.

Contribution

It demonstrates how solvent deuteration heterogeneities at different scales influence protein gel structure and interactions, providing new insights into gluten protein network heterogeneity.

Findings

Heterogeneous deuteration at different length scales in gluten gels

Inhomogeneous proton-deuterium exchange with 60 nm zones enriched in H

Deuteration induces phase separation at low protein concentrations

Abstract

The structure of model gluten protein gels prepared in ethanol/water is investigated by small angle X-ray (SAXS) and neutrons (SANS) scattering. We show that gluten gels display radically different SAXS and SANS profiles when the solvent is (at least partially) deuterated. The detailed analysis of the SANS signal as a function of the solvent deuteration demonstrates heterogeneities of sample deuteration at different length scales. The progressive exchange between the protons (H) of the proteins and the deuteriums (D) of the solvent is inhomogeneous and 60 nm large zones that are enriched in H are evidenced. In addition, at low protein concentration, in the sol state, solvent deuteration induces a liquid/liquid phase separation. Complementary biochemical and structure analyses show that the denser protein phase is more protonated and specifically enriched in glutenin, the polymeric fraction of gluten proteins. These findings suggest that the presence of H-rich zones in gluten gels would arise from the preferential interaction of glutenin polymers through a tight network of non-exchangeable intermolecular hydrogen bonds.