title: Protein phase behavior in aqueous solutions: crystallization, liquid-liquid phase separation, gels, and aggregates.
abstract: The aggregates and gels commonly observed during protein crystallization have generally been considered disordered phases without further characterization. Here their physical nature is addressed by investigating protein salting-out in ammonium sulfate and sodium chloride for six proteins (ovalbumin, ribonuclease A, soybean trypsin inhibitor, lysozyme, and beta-lactoglobulin A and B) at 4 degrees C, 23 degrees C, and 37 degrees C. When interpreted within the framework of a theoretical phase diagram obtained for colloidal particles displaying short-range attractive interactions, the results show that the formation of aggregates can be interpreted theoretically in terms of a gas-liquid phase separation for aggregates that are amorphous or gel-like. A notable additional feature is the existence of a second aggregation line observed for both ovalbumin and ribonuclease A in ammonium sulfate, interpreted theoretically as the spinodal. Further investigation of ovalbumin and lysozyme reveals that the formation of aggregates can be interpreted, in light of theoretical results from mode-coupling theory, as a kinetically trapped state or a gel phase that occurs through the intermediate of a gas-liquid phase separation. Despite the limitations of simple theoretical models of short-range attractive interactions, such as their inability to reproduce the effect of temperature, they provide a framework useful to describe the main features of protein phase behavior.
authors.affiliation: Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: André C
authors.initials: AC
authors.lastname: Dumetz
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Chockla
authors.forename: Eric W
authors.initials: EW
authors.lastname: Kaler
authors.forename: Abraham M
authors.initials: AM
authors.lastname: Lenhoff
mesh_terms: D000818:Animals; D002417:Cattle; D002645:Chickens; D003460:Crystallization; D005782:Gels; D009113:Muramidase / Q000737:chemistry; D010047:Ovalbumin / Q000737:chemistry; D020836:Protein Structure, Quaternary; D011506:Proteins / Q000737:chemistry*; D012259:Ribonuclease, Pancreatic / Q000737:chemistry; D012995:Solubility; D012996:Solutions; D013696:Temperature; D013997:Time Factors
chemical_list: D005782:Gels; D011506:Proteins; D012996:Solutions; D010047:Ovalbumin; D012259:Ribonuclease, Pancreatic; D009113:Muramidase