Blue copper proteins ligands, amino acid sequence

The central copper ion of the auracyanins is probably coordinated by two histidines, one cysteine, and a methionine residue. The auracyanins are unique among the small blue proteins in that they possess a methionine and a glutamine residue (see phytocyanins) which both could act as the fourth ligand coordinating the central copper ion. This copper center is surrounded by a hydro-phobic environment similar to that of the other small blue proteins [68]. Amino acid sequence comparisons place auracyanin in a phylogenetic tree at approximately equal distances from azurin and plastocyanin [68,92]. 

Residues with nonliganding side-chain characteristics that match the amino acid sequences of FVand FVIII with known copper ligands in ceruloplasmin are also presented. Codons for the conserved Leu residue at the position of the axial ligand in the blue copper site of BCB domain 2 of CPs are in parentheses. Residue numbers are for the mature proteins. 

Redox potentials for the different copper centers in the blue oxidases have been determined for all members of the group but in each case only for a limited number of species. The available data are summarized in Table VI 120, 121). The redox potentials for the type-1 copper of tree laccase and ascorbate oxidase are in the range of 330-400 mV and comparable to the values determined for the small blue copper proteins plastocyanin, azurin, and cucumber basic protein (for redox potentials of small blue copper proteins, see the review of Sykes 122)). The high potential for the fungal Polyporus laccase is probably due to a leucine or phenylalanine residue at the fourth coordination position, which has been observed in the amino-acid sequences of fungal laccases from other species (see Table IV and Section V.B). Two different redox potentials for the type-1 copper were observed for human ceruloplasmin 105). The 490-mV potential can be assigned to the two type-1 copper sites with methionine ligand and the 580-mV potential to the type-1 center with the isosteric leucine at this position (see Section V.B). The... 

In almost 30 blue copper proteins, all of which contain about 100 amino acids, the amino acid sequence has been determined. About a quarter of the amino acid sequence is common to all and so this sequence almost certainly contains the ligands which bond to the copper. In this way, the amino acids... 

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