Charged Protein Partitioning in Aqueous Polyethylene Glycol–Dextran Two-Phase Systems: Salt Effects

Abstract

This work continues our examination of the contribution of protein charge to partitioning in polyethylene glycol–dextran aqueous two-phase systems. The partitioning of T4 lysozyme and its charge–change mutants, both point mutations and fusion tails, in aqueous two-phase systems with NaCl, KCl, K₂SO₄, and potassium phosphate salts at concentrations from ca. 0.05–0.5 M are reported. Both salts and proteins have different distributions in systems with the same overall polymer concentration but different salts and salt concentrations. T4 lysozyme point mutants and fusion-tail mutants of the same charge display different partitioning behaviors. The point mutation mutants were best suited for distinguishing nonelectrostatic from electrostatic effects of the different salts on protein partitioning.

ACKNOWLEDGMENTS

We thank Dr. Brian Matthews for providing the cultures to produce the T4 lysozyme and mutants with charge-change point mutations, and Dr. Clark Ford of Iowa State University for guidance and facilities in preparing the genetic constructions. This material is based upon work supported by the National Science Foundation under Grant BCS-9108583. The government has certain rights in this material. Weiyu Fan was partially supported by the Biotechnology Byproducts Consortium under a contract from the US Department of Agriculture.