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Comparison between Protein-Polyethylene Glycol (PEG) Interactions and the Effect of PEG on Protein-Protein Interactions Using the Liquid-Liquid Phase Transition
 

Summary: Comparison between Protein-Polyethylene Glycol (PEG) Interactions and the Effect of
PEG on Protein-Protein Interactions Using the Liquid-Liquid Phase Transition
Ying Wang and Onofrio Annunziata*
Department of Chemistry, Texas Christian UniVersity, Fort Worth, Texas 76129
ReceiVed: August 29, 2006; In Final Form: NoVember 18, 2006
Phase transitions of protein aqueous solutions are important for protein crystallization and biomaterials science
in general. One source of thermodynamic complexity in protein solutions and their phase transitions is the
required presence of additives such as polyethylene glycol (PEG). To investigate the effects of PEG on the
thermodynamic behavior of protein solutions, we report measurements on the liquid-liquid phase separation
(LLPS) of aqueous bovine serum albumin (BSA) in the presence of relatively small amounts of PEG with an
average molecular weight of 1450 g/mol (PEG1450) as a model system. We experimentally characterize two
thermodynamically independent properties of the phase boundary: (1) the effect of PEG1450 concentration
on the LLPS temperature, (2) BSA/PEG1450 partitioning in the two liquid coexisting phases. We then use
a thermodynamic perturbation theory to relate the first property to the effect of PEG concentration on protein-
protein interactions and the second property to protein-PEG interactions. As criteria to determine the accuracy
of a microscopic model, we examine the model's ability to describe both experimental thermodynamic
properties. We believe that the parallel examination of these two properties is a valuable tool for verifying
the validity of existing models and for developing more accurate ones. For our system, we have found that
a depletion-interaction model satisfactorily explains both protein-PEG interactions and the effect of PEG
concentration on protein-protein interactions. Finally, due to the general importance of LLPS, we will

  

Source: Annunziata, Onofrio - Department of Chemistry, Texas Christian University
Benedek, George B. - Department of Physics, Massachusetts Institute of Technology (MIT)

 

Collections: Chemistry; Physics