title: Competition between metals for binding to methanobactin enables expression of soluble methane monooxygenase in the presence of copper.
abstract: It is well known that copper is a key factor regulating expression of the two forms of methane monooxygenase found in proteobacterial methanotrophs. Of these forms, the cytoplasmic, or soluble, methane monooxygenase (sMMO) is expressed only at low copper concentrations. The membrane-bound, or particulate, methane monooxygenase (pMMO) is constitutively expressed with respect to copper, and such expression increases with increasing copper. Recent findings have shown that copper uptake is mediated by a modified polypeptide, or chalkophore, termed methanobactin. Although methanobactin has high specificity for copper, it can bind other metals, e.g., gold. Here we show that in Methylosinus trichosporium OB3b, sMMO is expressed and active in the presence of copper if gold is also simultaneously present. Such expression appears to be due to gold binding to methanobactin produced by M. trichosporium OB3b, thereby limiting copper uptake. Such expression and activity, however, was significantly reduced if methanobactin preloaded with copper was also added. Further, quantitative reverse transcriptase PCR (RT-qPCR) of transcripts of genes encoding polypeptides of both forms of MMO and SDS-PAGE results indicate that both sMMO and pMMO can be expressed when copper and gold are present, as gold effectively competes with copper for binding to methanobactin. Such findings suggest that under certain geochemical conditions, both forms of MMO may be expressed and active in situ. Finally, these findings also suggest strategies whereby field sites can be manipulated to enhance sMMO expression, i.e., through the addition of a metal that can compete with copper for binding to methanobactin.
authors.affiliation: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Bhagyalakshmi
authors.initials: B
authors.lastname: Kalidass
authors.affiliation: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Muhammad Farhan
authors.initials: MF
authors.lastname: Ul-Haque
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, USA.
authors.forename: Bipin S
authors.initials: BS
authors.lastname: Baral
authors.affiliation: Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, Iowa, USA.
authors.forename: Alan A
authors.initials: AA
authors.lastname: DiSpirito
authors.affiliation: Department of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan, USA jsemrau@umich.edu.
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Semrau
mesh_terms: D003300:Copper / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D015870:Gene Expression; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D006046:Gold / Q000378:metabolism; D007093:Imidazoles / Q000378:metabolism*; D020602:Methylosinus trichosporium / Q000201:enzymology* / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D010105:Oxygenases / Q000096:biosynthesis*; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D007093:Imidazoles; D009842:Oligopeptides; C491147:methanobactin; D006046:Gold; D003300:Copper; D010105:Oxygenases; C021555:methane monooxygenase