Equation of state and structure of highly concentrated globular protein solutions

Abstract

In food technology, proteins are classically subject to operations leading to high local concentrations (membrane filtration, drying, stabilization of dispersed systems through the formation of dense interfacial films). However, few studies have for now been conducted on the behaviour of globular proteins in “highly crowded” situations, despite interesting observations in some cases and a growing interest in the subject [1,2]. Our goal is to study the crowding of proteins in an extended concentrIn food technology, proteins are classically subject to operations leading to high local concentrations (membrane filtration, drying, stabilization of dispersed systems through the formation of dense interfacial films). However, few studies have for now been conducted on the behaviour of globular proteins in “highly crowded” situations, despite interesting observations in some cases and a growing interest in the subject [1,2]. Our goal is to study the crowding of proteins in an extended concentration range, up to volume fractions about 0.5, using highly concentrated solutions obtained via the osmotic stress method [3]. Recently, this method has been used to study the behaviour of milk casein micelles upon concentration [4]. Equations of state, which relate concentration and osmotic pressure, were established for two well-known globular proteins, lysozyme and ovalbumin, in different charge and ionic strength conditions. We then conducted a SAXS study of the structure of the highly concentrated lysozyme and ovalbumin samples. We showed that the structure of the samples, depending on the protein, the charge and the range of interactions, underwent drastic structural changes and phase transitions upon concentration. In this communication, we will discuss the equations of state obtained for lysozyme and ovalbumin, then the structural properties of crowded lysozyme and ovalbumin as determined by SAXS studies, in the light of the molecular structure and physico-chemical properties of these two proteins, as well as the general behaviour and interaction properties of proteins