Protein precipitation by polyethylene glycol: a generalized model based on hydrodynamic radius

Area of Science:

• Biochemistry
• Chemical Engineering
• Polymer Science

Background:

• Protein precipitation using polyethylene glycol (PEG) is a common bioprocessing technique.
• Current classification of PEG precipitants by molecular weight has limitations in predicting efficiency.
• Higher molecular weight PEGs increase efficiency but also viscosity, complicating their use.

Purpose of the Study:

• To propose a new model for protein precipitation efficiency based on PEG hydrodynamic radius (r(h,PEG)).
• To develop a numerical relation that models PEG precipitation exclusively using hydrodynamic radii.
• To elucidate the significance of r(h,PEG) in protein precipitation mechanisms.

Main Methods:

• Formulated a general expression for PEG precipitation efficiency based on r(h,PEG).
• Fitted coefficients using empirical protein solubility data to linearize the expression.
• Validated the model against independent solubility data for various protein systems.

Main Results:

• Developed a simple numerical relation linking PEG precipitation efficiency to r(h,PEG) and protein hydrodynamic radius (r(h,prot)).
• The model accounts for environmental conditions and PEG branching effects.
• Predictions showed reasonable agreement with experimental solubility data, with minor deviations for small/large proteins and mixtures.

Conclusions:

• PEG hydrodynamic radius (r(h,PEG)) is a more comprehensive parameter than molecular weight for characterizing PEG precipitation efficiency.
• The developed model offers a refined understanding of PEG-protein interactions and precipitation mechanisms.
• This work provides a basis for improved selection criteria for PEG precipitants in bioprocessing.