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Journal of Biochemistry Advance Access published online on July 23, 2007
Journal of Biochemistry, doi:10.1093/jb/mvm136
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© 2007 The Japanese Biochemical Society

Identification of a blue copper protein from Hyphomicrobium denitrificans and its functions in the periplasm

Daisuke Hira, Masaki Nojiri, Kazuya Yamaguchi and Shinnichiro Suzuki*

Department of Chemistry, Graduate School of Science, Osaka University, 1-16 Machikaneyama, Toyonaka, Osaka 560-0043, Japan

*To whom correspondence should be addressed. Tel: +81-6-6850-5767, Fax: +81-6-6850-5785, E-mail: bic{at}ch.wani.osaka-u.ac.jp

Received April 19, 2007; Accepted June 13, 2007


  Abstract

It has been known that the methylotrophic denitrifying bacteria have the specific electron transfer chains, involving in "methanol oxidation" and "denitrification", in the periplasm. Recently, a unique blue copper protein (HdBCP) has been isolated from the methanol-grown methylotrophic denitrifying bacterium, Hyphomicrobium denitrificans. HdBCP is a 14.5-kDa protein and contains one copper atom in the molecule. The electronic absorption spectrum of HdBCP exhibits two absorption maxima near 450 and 750 nm comparable with the intense 600-nm band ({epsilon}450/{epsilon}600 = ca. 0.9). The rhombic electron paramagnetic resonance spectrum shows clearly that the copper center is a "perturbed" type 1 copper geometry. Stopped-flow kinetics indicates that HdBCP accepts efficiently an electron from cytochrome cL (k2 = 4.0 x 106 M-1 s-1 at 25.0 °C), which is a physiological electron acceptor for methanol dehydrogenase. According to cloning and DNA sequencing of the structural gene, the deduced amino acid sequence shows significant similarities with pseudoazurins, which are a physiological electron donor for Cu-containing nitrite reductase from the denitrifying bacteria. Based on these results, we discuss the role of HdBCP in the electron-flow system, which link "methanol oxidation" and "denitrification" together.

Key Words: blue copper protein, electron transfer, type 1 copper, methylotroph, denitrification


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