Copper clean-up idea

Hmmmmmm.... This is interesting...

Blue or 'type-1' copper proteins are small proteins which bind a single copper atom and which are characterized by an intense electronic absorption band near 600 nm [MEDLINE:84135769], [MEDLINE:93164266]. The most well known members of this class of proteins are the plant chloroplastic plastocyanins, which exchange electrons with cytochrome c6, and the distantly related bacterial azurins, which exchange electrons with cytochrome c551. This family of proteins also includes amicyanin from bacteria such as Methylobacterium extorquens or Thiobacillus versutus that can grow on methylamine; auracyanins A and B from Chloroflexus aurantiacus [MEDLINE:92202194]; blue copper protein from Alcaligenes faecalis; cupredoxin (CPC) from cucumber peelings [MEDLINE:93106154]; cusacyanin (basic blue protein; plantacyanin, CBP) from cucumber; halocyanin from Natrobacterium pharaonis [MEDLINE:94253046], a membrane associated copper-binding protein; pseudoazurin from Pseudomonas; rusticyanin from Thiobacillus ferrooxidans [MEDLINE:91348256]; stellacyanin from the Japanese lacquer tree; umecyanin from horseradish roots; and allergen Ra3 from ragweed. This pollen protein is evolutionary related to the above proteins, but seems to have lost the ability to bind copper. Although there is an appreciable amount of divergence in the sequences of all these proteins, the copper ligand sites are conserved.

Crystal structure of plantacyanin, a basic blue cupredoxin from spinach
Oliver Einsle1, , Zara Mehrabian2, Robert Nalbandyan2 and Albrecht Messerschmidt1

(1) Max-Planck-Institut für Biochemie, Abteilung Strukturforschung, Am Klopferspitz 18a, 82152 Martinsried, Germany
(2) University of Maryland, School of Medicine, Anesthesiology Department, W. Baltimore St., Baltimore, MD 21201, USA





The crystal structure of the basic blue protein (plantacyanin) from spinach (SBP) has been solved to a resolution of 2.05 Å by molecular replacement using the homologous protein from cucumber (CBP) as a model. Although the sequence identity of 58% between both proteins is only moderate, the three-dimensional structures turned out to be highly similar and the buried residues, which form the hydrophobic core of the protein, are almost completely conserved. However, the redox potentials of both proteins differ by 40 mV, and a comparison of the two structures leads to a single lysine replacing a proline in the cucumber sequence, which causes a shift of the peptide chain and thus a subtle distortion of the copper ligand geometry in respect to CBP. The crystal contained three monomers of SBP in the asymmetric unit which show considerable variations in outer loop regions owing to crystal packing, but not in the regions presumed to be essential for redox partner recognition and redox potential fine tuning of the copper centers. Still, bond length variations at the copper site are at the same scale between the monomers of SBP as they are in respect to CBP, indicating that in the oxidized state the protein does not impose a high conformational strain on the copper.

VII-D-1 Reduction and Oxidation Processes of Blue Copper Proteins, Azurin, Pseudoazurin, Umecyanin, Stellacyanin, Plantacyanin, And Plastocyanin Approached by Cyclic and Potential Step Voltammetries
Takeshi SAKURAI, Fumitaka NOSE, Takayuki FUJIKI and Schinnichiro SUZUKI (Osaka Univ.)

[Bull. Chem. Soc. Jpn. 69, 2855 (1996)]

Direct electrochemistry of a series of blue copper proteins: azurin, pseudoazurin, umecyanin, stellacyanin, plantacyanin, and plastocyanin has been performed at a gold electrode modified with di-4-pyridyl disulfide and/or at a bare glassy carbon electrode. Well-resolved cyclic voltammograms with peak separation, (DELTA)Ep = 55 - 100 mV were obtained. Protein molecules associate with the electrode surface through both electrostatic and hydrophobic interactions, of which the predominant one differs according to the combination of protein and electrode. Double-step voltammetry showed that redox processes of blue copper proteins depend profoundly on the translocation of the molecules (diffusion and/or change of orientation) at the electrode surface. The heterogeneous rate constants at pH 6.0 and 25 °C for both reduction and oxidation processes were independently determined to be the order of 10-3 to 10-4 cms-1 by single-step voltammetry and were compared with those determined by cyclic voltammetry. Further, activation parameters for redox processes of some blue copper proteins have been determined from temperature dependence studies. The reaction pathway of blue copper proteins was discussed.