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Copper-Binding Properties and Structures of Methanobactins from Methylosinus trichosporium OB3b

Lookup NU author(s): Dr Abdelnasser El Ghazouani, Dr Arnaud Basle, Dr Susan Firbank, Dr Charles Knapp, Dr Joseph Gray, Professor David Graham, Professor Christopher Dennison

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Abstract

Methanobactins (mbs) are a class of copper-binding peptides produced by aerobic methane oxidizing bacteria (methanotrophs) that have been linked to the substantial copper needs of these environmentally important microorganisms. The only characterized mbs are those from Methylosinus trichosporium OB3b and Methylocystis strain SB2. M. trichosporium OB3b produces a second mb (mb-Met), which is missing the C-terminal Met residue from the full-length form (FL-mb). The as-isolated copper-loaded mbs bind Cu(I). The absence of the Met has little influence on the structure of the Cu(I) site, and both molecules mediate switchover from the soluble iron methane monooxygenase to the particulate copper-containing enzyme in M. trichosporium OB3b cells. Cu(II) is reduced in the presence of the mbs under our experimental conditions, and the disulfide plays no role in this process. The Cu(I) affinities of these molecules are extremely high with values of (6-7) x 10(20) M-1 determined at pH >= 8.0. The affinity for Cu(I) is 1 order of magnitude lower at pH 6.0. The reduction potentials of copper-loaded FL-mb and mb-Met are 640 and 590 mV respectively, highlighting the strong preference for Cu(I) and indicating different Cu(II) affinities for the two forms. Cleavage of the disulfide bridge results in a decrease in the Cu(I) affinity to similar to 9 x 10(18) M-1 at pH 7.5. The two thiolates can also bind Cu(I), albeit with much lower affinity (similar to 3 x 10(15) M-1 at pH 7.5). The high affinity of mbs for Cu(I) is consistent with a physiological role in copper uptake and protection.


Publication metadata

Author(s): El Ghazouani A, Basle A, Firbank SJ, Knapp CW, Gray J, Graham DW, Dennison C

Publication type: Article

Publication status: Published

Journal: Inorganic Chemistry

Year: 2011

Volume: 50

Issue: 4

Pages: 1378-1391

Print publication date: 21/01/2011

ISSN (print): 0020-1669

ISSN (electronic): 1520-510X

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/ic101965j

DOI: 10.1021/ic101965j


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