Characterization of His-X3-His sites in α-helices of synthetic metal-binding bovine somatotropin

Variants of bovine somatotropin have been engineered to contain synthetic metal-binding sites consisting of two solvent-exposed histidines separated by a single turn of an α-helix (His-X 3 -His variants). The affinities of these proteins for Cu(II) were characterized by measuring their partition coefficients in an aqueous two-phase polymer system. The partition coefficients were used to generate binding constants for formation of a complex between the engineered metal-binding site and Cu(II) chelated to an iminodiacetic acid derivative of polyethylene glycol. Criteria for choosing positions for incorporating metal-binding sites are discussed