Molecular binding mechanisms between grape seed polypeptides and wine anthocyanins by fluorescence spectroscopy and computational techniques

Abstract

In recent years, proteins endogenous to grape have become of great interest to the wine industry because they represent a new alternative to other biopolymers subjected to more legal restrictions (i.e. animal origin and synthetics) that can be used in technological applications to modulate sensory attributes such as wine color and have a positive impact on wine quality.
Due to their great techno-functional value, some major protein components of grape seed endosperm have been identified and its potential use for color protection purposes have been already tested in wines at experimental scale. Notwithstanding, the capability of proteins to modulate sensory properties is highly dependent on their structural features, their ability to form specific 3D conformations, and the interaction with other molecules present in food matrices such as anthocyanin pigments in wines. Recently, we have confirmed by means of theoretical studies that grape seed  globulins can stablish different types of interactions (hydrogen bonding, alkyl and π-π) with the main grape anthocyanin (malvidin 3-gl).To date, however, such as interactions has been scarcely studied. Although a basic molecular interaction mechanism similar to copigmentation has been suggested, many questions still remain unclarified. In this sense, a deeper molecular understanding of the grape seed protein-anthocyanin interactions is needed to better define their potential uses and technological applications.
Thus, the main objective of this work was to explore new molecular binding mechanisms between grape seed polypeptides and wine anthocyanins in model wine solutions through fluorescence spectroscopy and computational techniques. For this purpose, fluorescence extinction spectroscopy was used to experimentally confirm the possible interaction mechanisms, the affinity constants, the stoichiometry of the complexes and other thermodynamic parameters. In addition, molecular modelling techniques, such as docking studies, were used to model the  most energetically favorable binding sites of wine anthocyanins on the grape seed polypeptide. Results will provide insights and substantial information about protection to colors expressed by anthocyanins in red wine.