期刊
BIOCHEMISTRY
卷 45, 期 34, 页码 10191-10198出版社
AMER CHEMICAL SOC
DOI: 10.1021/bi060693h
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资金
- NIGMS NIH HHS [GM70473, GM8061] Funding Source: Medline
Methane monooxygenase (MMO) enzymes catalyze the oxidation of methane to methanol in methanotrophic bacteria. Several strains of methanotrophs, including Methylococcus capsulatus ( Bath), express a membrane-bound or particulate MMO (pMMO) at high copper-to-biomass ratios and a soluble MMO (sMMO) form when copper is limited. The mechanism of this copper switch is not understood. The mmoS gene, located downstream of the sMMO operon, encodes a sensor protein that is part of a two-component signaling system and has been proposed to play a role in the copper switch. MmoS from M. capsulatus (Bath) has been cloned, expressed, and purified. The purified protein is a tetramer of molecular mass 480 kDa. Optical spectra indicate that MmoS contains a flavin cofactor, identified as flavin adenine dinucleotide (FAD) by fluorescence spectroscopy and chromatographic analysis. The redox potential of the MmoS-bound FAD, which binds within the N-terminal PAS-PAC domains, is -290 +/- 2 mV at pH 8.0 and 25 degrees C. Despite extensive efforts, MmoS could not be loaded with Cu-I or Cu-II, indicating that MmoS does not sense copper directly. These data suggest that MmoS functions as a redox sensor and provide new insight into the copper-mediated regulation of sMMO expression.
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