Novel Metal-Affinity Protein Separations

Abstract

The affinity exhibited by proteins for chelated metals has been exploited in two new protein purification techniques: metal affinity aqueous two-phase extraction and metal affinity precipitation. Metal-chelating derivatives of polyethylene glycol have been used to selectively enhance the partition coefficients of proteins in aqueous two-phase separations. When the metal chelate is attached to both ends of the water-soluble polymer, the resulting bis-chelate is an effective precipitating agent for proteins that contain multiple surface-accessible histidines. Parameters important in the design and application of these affinity separations include pH, the number of accessible histidines on the proteins, and the design of the metal affinity ligand. These techniques offer the potential for large-scale application and integration of an affinity separation early in the purification process.

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