On the Evolution of Blue Proteins

Amino acid sequences of 8 plastocyanins, 8 azurins, stellacyanin, two regions in human ceruloplasmin (ferroxidase)--all of which proteins are known to bind a blue (type 1) copper--and subunit II of bovine mitochondrial cytochrome c oxidase were compared by statistical methods to assess similarities and derive possible evolutionary relationships. It is suggested that all of the examined proteins are monophyletic. The two ceruloplasmin partial sequences clearly demonstrate that this protein has undergone a duplication. A calculated most parcimonious phylogenetic tree shows the divergence of the azurin and plastocyanin ancestor to be the earliest event. Stellacyanin and later the blue oxidase (ceruloplasmin) evolved from the plastocyanin branch, which the cytochrome c oxidase subunit evolved from the azurin ancestor.