Biochemical characterization of MmoS, a sensor protein involved in copper-dependent regulation of soluble methane monooxygenase

Uchechi E. Ukaegbu, Shannon Henery, Amy C. Rosenzweig*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

18 Scopus citations

Abstract

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 °C. Despite extensive efforts, MmoS could not be loaded with CuI or CuII, 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.

Original languageEnglish (US)
Pages (from-to)10191-10198
Number of pages8
JournalBiochemistry
Volume45
Issue number34
DOIs
StatePublished - Aug 29 2006

ASJC Scopus subject areas

  • Biochemistry

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