Evolution of blue copper proteins

Abstract

The evolutionary relationships of blue copper proteins are reviewed. Five homologous families of small blue proteins are recognized. Despite differences in length their peptide chains can all be accommodated into the eight-stranded fold of plastocyanin with some adjustments at three of the loops and the two termini. The C-termini of the blue oxidases ceruloplasmin and Neurospora laccase also fit into this fold and they are suggested to be homologous to the small blue proteins. The alignment of their amino acid sequences suggest some of the histidines to be binding active site copper. A superposition of the structures of poplar plastocyanin and bovine Cu-Zn superoxide dismutase (SOD) showed that 68 out of 99 alpha-carbons in plastocyanin overlapped with corresponding atoms in SOD with a rms distance of 2.99 A. In addition three of the histidine residues that were proposed to be copper-binding in laccase and ceruloplasmin aligned with ligands to the Cu-Zn pair in a SOD. Thus also SOD might be related to the blue proteins.