Effects of ammonium sulfate and sodium chloride concentration on PEG/protein liquid-liquid phase separation.
When added to protein solutions, poly(ethylene glycol) (PEG) creates an effective attraction between protein molecules due to depletion forces. This effect has been widely used to crystallize proteins, and PEG is among the most successful crystallization agents in current use. However, PEG is almost always used in combination with a salt at either low or relatively high concentrations. Here the effects of sodium chloride and ammonium sulfate concentration on PEG 8000/ovalbumin liquid-liquid (L-L) phase separation are investigated. At low salt the L-L phase separation occurs at decreasing protein concentration with increasing salt concentration, presumably due to repulsive electrostatic interactions between proteins. At high salt concentration, the behavior depends on the nature of the salt. Sodium chloride has little effect on the L-L phase separation, but ammonium sulfate decreases the protein concentration at which the L-L phase separation occurs. This trend is attributed to the effects of critical fluctuations on depletion forces. The implications of these results for designing solution conditions optimal for protein crystallization are discussed.
Dumetz
André C
AC
Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, Newark, DE 19716, USA.
Lewus
Rachael A
RA
Lenhoff
Abraham M
AM
Kaler
Eric W
EW
D000645:Ammonium Sulfate / Q000737:chemistry*; D000818:Animals; D002627:Chemistry, Physical / Q000379:methods; D002645:Chickens; D004529:Egg White; D006863:Hydrogen-Ion Concentration; D010047:Ovalbumin / Q000737:chemistry; D044367:Phase Transition; D011092:Polyethylene Glycols / Q000737:chemistry*; D011485:Protein Binding; D012492:Salts / Q000737:chemistry / Q000494:pharmacology; D012965:Sodium Chloride / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
D012492:Salts; D011092:Polyethylene Glycols; D012965:Sodium Chloride; D010047:Ovalbumin; D000645:Ammonium Sulfate