Identification of a bis-molybdopterin intermediate in molybdenum cofactor biosynthesis in escherichia coli

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Abstract

The molybdenum cofactor is an important cofactor, and its biosynthesis is essential for many organisms, including humans. Its basic form comprises a single molybdopterin (MPT) unit, which binds a molybdenum ion bearing three oxygen ligands via a dithiolene function, thus forming Mo-MPT. In bacteria, this form is modified to form the bis-MPT guanine dinucleotide cofactor with two MPT units coordinated at one molybdenum atom, which additionally contains GMPs bound to the terminal phosphate group of the MPTs (bis-MGD). The MobA protein catalyzes the nucleotide addition to MPT, but the mechanism of the biosynthesis of the bis-MGD cofactor has remained enigmatic. We have established an in vitro system for studying bis-MGD assembly using purified compounds. Quantification of the MPT/molybdenum and molybdenum/ phosphorus ratios, time-dependent assays for MPT and MGD detection, and determination of the numbers and lengths of Mo-S and Mo-O bonds by X-ray absorption spectroscopy enabled identification of a novel bis-Mo-MPT intermediate on MobA prior to nucleotide attachment. The addition of Mg-GTP to MobA loaded with bis-Mo-MPT resulted in formation and release of the final bis-MGD product. This cofactor was fully functional and reconstituted the catalytic activity of apo-TMAO reductase (TorA). We propose a reaction sequence for bis-MGD formation, which involves 1) the formation of bis-Mo-MPT, 2) the addition of two GMP units to form bis-MGD on MobA, and 3) the release and transfer of the mature cofactor to the target protein TorA, in a reaction that is supported by the specific chaperone TorD, resulting in an active molybdoenzyme.

Details

Authors
  • Stefan Reschke
  • Kajsa G.V. Sigfridsson
  • Paul Kaufmann
  • Nils Leidel
  • Sebastian Horn
  • Klaus Gast
  • Carola Schulzke
  • Michael Haumann
  • Silke Leimkühler
External organisations
  • University of Potsdam
  • Free University of Berlin
  • University of Greifswald
Original languageEnglish
Pages (from-to)29736-29745
Number of pages10
JournalJournal of Biological Chemistry
Volume288
Issue number41
Publication statusPublished - 2013 Oct 11
Publication categoryResearch
Peer-reviewedYes
Externally publishedYes