DIFFERENT ORIGINS OF METAL-BINDING SITES IN BINUCLEAR COPPER PROTEINS, TYROSINASE AND HEMOCYANIN

The primary structures of five binuclear copper proteins (two tyrosinases, two arthropodan, and one molluscan hemocyanin) are compared. All proteins showed a highly homologous region of 56 amino acids in the C-terminal parts containing three invariant histidines previously identified as ligands to Cu B in Panulirus interruptus hemocyanin by x-ray crystallography (Gaykema et al., Nature 309, 23-29 (1984)). In contrast, a very different ligand environment is obsreved for Cu A. It is concluded that the Cu B site in tyrosinases and hemocyanins originated during the earliest period of life, whereas Cu A must have evolved independently subsequent to the invention of Cu B. Furthermore, the two copper sites appear to be unique for these proteins because they are absent in ceruloplasmin, a multicopper protein containing one binuclear and two different mononuclear sites.