FURTHER CHARACTERIZATION OF THE N-TERMINAL COPPER(II)-BINDING AND NICKEL(II)-BINDING MOTIF OF PROTEINS - STUDIES OF METAL-BINDING TO CHICKEN SERUM-ALBUMIN AND THE NATIVE SEQUENCE PEPTIDE

We have investigated the Cu(II)-and Ni(II)-binding properties of chicken serum albumin (CSA) and of the native sequence tripeptide derived from the N-terminus of this protein. Spectrophotometric and equilibrium dialysis experiments demonstrate that Cu(II) and Ni(II) bind non-specifically at the N-terminus of CSA. Proton displacement studies show that the histidine residue in the fourth position of the protein does not appear to participate in the binding of the two metals. Consistent results were obtained with the native sequence tripeptide L-aspartyl-L-alanyl-L-glutamic acid N-methylamide. The results presented here demonstrate that neither the glutamic acid residue in the third position nor the histidine in the fourth position participate in the binding of Cu(II) and Ni(II) to CSA. It is known, however, that a number of other albumins with a histidine residue in the third position possess high-affinity Cu(II)- and Ni(II)-binding sites. Our results provide further evidence that the N-terminal Cu(II)/Ni(Il)-binding motif requires a histidine at the third position in order to bind Cu(II) and Ni(II) specifically.