Blue copper proteins sequences

The second class consists of multidomain blue copper proteins composed of exclusively two or more BCB domains and includes nitrite reductase (Section IV, E), multicopper blue oxidases such as laccase, ascorbate oxidase, ceruloplasmin, and hephaestin (Section VII), and some sequences found in extreme halophilic archaea (see Section V, E). 

Blue copper proteins have been purified and biochemically characterized from Archaea, Bacteria, and Eukarya. Such ubiquitous distribution suggests an important ancient role. A survey of sequence databases reveals genes encoding blue copper proteins that display characteristics often quite different from those of well-studied canonical (traditional) blue copper proteins. For example, there are modular proteins where the domains that bind type 1 copper are fused with structurally distinct and evolutionarily unrelated sequence motifs (Figure 1). While these additional domains do not usually contribute directly to the ftmction of a blue copper protein, they do so indirectly by facilitating protein translocation to a specific cellular compartment. Together, these blue copper proteins can be combined into a large superfamily which can be subdivided into three classes as described below. 

Halocyanin and sulfocyanin are archaebacterial cupre-doxins that are attached to peripheral membranes through a lipid anchor at their N-terminus. Halocyanin was the first cupredoxin purified from an archaeon, haloalkaliphilic Natronobacterium pharaonis These cells live in high pH (around 10-11) and in extreme salinity (30%) environments. The presence of the blue copper protein, sulfocyanin in Sul-folobus acidocaldarius was first predicted from its gene sequence. It has been subsequently purified as a recombinant protein and shown to bind a single copper ion with spectroscopic properties typical for a blue copper site. ... 

Plantacyanin is represented in the Arabidopsis genome by a single gene, while rice has nine. Multiple plantacyanin sequences can also be identified in plant species such as wheat, barley, and maize. Spinach plantacyanin is 91-amino acids long and is perhaps the smallest blue copper protein known. 

Similar sequence alignments also revealed that CcOII shared similar structural homology with the mononuclear type 1 blue copper proteins and the main difference between the two families of proteins resided in the FG loop sequence (Figure The conversion of the blue copper center... 

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... 

A structurally based amino-acid sequence alignment strongly suggests a three-domain structure for laccase, closely related to ascorbate oxidase, and a six-domain structure for ceruloplasmin. These domains demonstrate homology with the small blue copper proteins. The relationship suggests that laccase, like ascorbate oxidase, has a mononuclear blue copper in domain 3 and a trinuclear copper between domain 1 and domain 3, and ceruloplasmin has mononuclear copper ions in domains 2, 4, and 6 and a trinuclear copper between domain 1 and domain 6. 

Rusticyanin has a high reduction potential (680 mV), which is similar to that for the Type 1 Cu center in fungal as opposed to tree laccase (785 mV) (73). This trend is so far unexplained. From the sequence and EXAFS studies, His-Cys-His-Met coordination is a reasonable possibility for rusticyanin (55). It may well be that the reduction potential is determined by effects of a polypeptide backbone on Cu—S(Cys) and Cu—S(Met) bond distances and the Cu ligand field (74). If this is the case, however, rusticyanin would be expected to have one or both Cu—S distances shorter than in other blue copper proteins, which is not borne out by information from EXAFS (Table IV). A further possibility that the Cu(I) form is three-coordinate, as in the case of plasto-cyanin at low pH (Fig. 2), has no strong support at present (75). 

A final point concerns the variability in number of amino acids separating the residues coordinating the Cu active site, and the possible controlling influence this might have. Available information is summarized in Table VI. In the case of azurin and pseudoazurin, there is the additional influence of the peptide C=0 on coordination at the Cu. All of the blue copper proteins have similar features, with coordination of the copper to one His from the first part of the sequence, and three other residues from the latter part. At present there appears to be no... 

Nunzi F, Woudstra M, Compese D, Bonicel J, Morin D, Bruschi M (1993) Amino-acid sequence of rusticyanin from Thiobacillus ferrooxidans and its comparison with other blue copper proteins. Biochim Biophys Acta 1162 28-34... 

Ronk M, Shively JE, Shute EA, Blake RC Jr (1991) Amino acid sequence of the blue copper protein rusticyanin from Thiobacillus ferrooxidans. Biochemistry 30 9435-9442 Rothfus JA, Smith EL (1965) Amino acid sequence of rhesus monkey heart cytochrome c. J Biol Chem 240 4277-4283... 

It is clear from Table 1 and Figures 2 and 3 how solvation affects the cyclic voltammetric results. The behaviour of [Cu(bddh)(NO )2] and [Cu(bddh)(Hdmpz)](BF/)2> both soluble in MeCN with no detectable decomposition, can be considered quasi-reversible, diffusion controlled (currents varied linearly with the square root of the scan rates), one-electron redox processes, involving a sequence Cu(II)-Cu(I)-Cu(II). Their half-wave potentials are practically independent of the scan rate their values, +555 mV vs. SCE (ca.+795 vs. NHE) and +525 mV vs. SCE (ca.+765 vs. NHE), respectively, are of the order of magnitude of the highest redox potentials found for the blue copper proteins [7]. 

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