title: Effect of polyethylene glycol on the liquid-liquid phase transition in aqueous protein solutions.
abstract: We have studied the effect of polyethylene glycol (PEG) on the liquid-liquid phase separation (LLPS) of aqueous solutions of bovine gammaD-crystallin (gammaD), a protein in the eye lens. We observe that the phase separation temperature increases with both PEG concentration and PEG molecular weight. PEG partitioning, which is the difference between the PEG concentration in the two coexisting phases, has been measured experimentally and observed to increase with PEG molecular weight. The measurements of both LLPS temperature and PEG partitioning in the ternary gammaD-PEG-water systems are used to successfully predict the location of the liquid-liquid phase boundary of the binary gammaD-water system. We show that our LLPS measurements can be also used to estimate the protein solubility as a function of the concentration of crystallizing agents. Moreover, the slope of the tie-lines and the dependence of LLPS temperature on polymer concentration provide a powerful and sensitive check of the validity of excluded volume models. Finally, we show that the increase of the LLPS temperature with PEG concentration is due to attractive protein-protein interactions.
authors.affiliation: Department of Physics, Center for Materials Science and Engineering, and Materials Processing Center, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA.
authors.forename: Onofrio
authors.initials: O
authors.lastname: Annunziata
authors.forename: Neer
authors.initials: N
authors.lastname: Asherie
authors.forename: Aleksey
authors.initials: A
authors.lastname: Lomakin
authors.forename: Jayanti
authors.initials: J
authors.lastname: Pande
authors.forename: Olutayo
authors.initials: O
authors.lastname: Ogun
authors.forename: George B
authors.initials: GB
authors.lastname: Benedek
mesh_terms: D000818:Animals; D002417:Cattle; D011092:Polyethylene Glycols / Q000737:chemistry*; D012996:Solutions; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry; D038222:gamma-Crystallins / Q000737:chemistry*
chemical_list: D012996:Solutions; D013501:Surface-Active Agents; D038222:gamma-Crystallins; D014867:Water; D011092:Polyethylene Glycols