title: Water-soluble, recombinant CuA-domain of the cytochrome ba3 subunit II from Thermus thermophilus.
abstract: Recently, the genes of cytochrome ba3 from thermus thermophilus [Keightley, J.A., et al. (1995) J. Biol. Chem. 270, 20345-20358], a homolog of the heme-copper oxidase family, have been cloned. We report here expression of a truncated gene, encoding the copper A (CuA) domain of cytochrome ba3, that is regulated by a T7 RNA polymerase promoter in Escherichia coli. The CuA-containing domain is purified in high yields as a water-soluble, thermostable, purple-colored protein. Copper analysis by chemical assay, mass spectrometry, X-ray fluorescence, and EPR spin quantification show that this protein contains two copper ions bound in a mixed-valence state, indicating that the CuA site in cytochrome ba3, is a binuclear center. The absorption spectrum of the CuA site, free of the heme interference in cytochrome ba3, is similar to the spectra of other soluble fragments from the aa3-type oxidase of Parachccus denitrificans [Lappalainen, P., et al. (1993) J. Biol Chem. 268, 26416-26421] and the caa3-type oxidase of Bacillus subtilis [von Wachenfeldt, C. et al. (1994) FEBS Lett. 340, 109-113]. There are intense bands at 480 nm (3100 M(-1) cm(-1)) and 530 nm (3200 M(-1) cm(-1)), a band in the near -IR centered at 790 nm (1900 M(-1) cn(-1)), and a weaker band at 363 nm (1300M(-1) cm(-1)). The visible CD spectrum shows a positive-going band at 460 nm and a negative-going band at 527 nm, the opposite signs of which may result from the binuclear nature of the site. The secondary structure prediction from the far-UV CD spectrum indicates that this domain is predominantly beta-sheet, in agreement with the recent X-ray structure reported for the complete P. denitrificans cytochrome aa3 molecule [Iwata, S., et al. (1995) Nature 376, 660-669] and the engineered, purple CyoA protein [Wilmanns, M., et al. (1996) Proc. Natl Acad. Sci. U.S.A. 92, 11955-11959]. However, the thermostability of the fragment described here (Tm approximately 80 degrees C) and the stable binding of copper over a broad pH range (pH 3-9) suggest this protein may be uniquely suitable for detailed physical-chemical study.
authors.affiliation: Division of Chemistry and Chemical Engineering, California Institute ofTechnology, Pasadena, 91125, USA.
authors.forename: C E
authors.initials: CE
authors.lastname: Slutter
authors.forename: D
authors.initials: D
authors.lastname: Sanders
authors.forename: P
authors.initials: P
authors.lastname: Wittung
authors.forename: B G
authors.initials: BG
authors.lastname: Malmström
authors.forename: R
authors.initials: R
authors.lastname: Aasa
authors.forename: J H
authors.initials: JH
authors.lastname: Richards
authors.forename: H B
authors.initials: HB
authors.lastname: Gray
authors.forename: J A
authors.initials: JA
authors.lastname: Fee
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D003300:Copper / Q000737:chemistry; D003573:Cytochrome b Group / Q000737:chemistry*; D017931:DNA Primers / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D003576:Electron Transport Complex IV / Q000737:chemistry*; D008667:Metalloproteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins; D012995:Solubility; D016963:Thermus thermophilus / Q000201:enzymology*; D014867:Water / Q000737:chemistry
chemical_list: D003573:Cytochrome b Group; D017931:DNA Primers; D008667:Metalloproteins; D011994:Recombinant Proteins; D014867:Water; D003300:Copper; C058557:cytochrome ba3; D003576:Electron Transport Complex IV