Crystal structures of the methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath): Implications for substrate gating and component interactions

Amy C. Rosenzweig, Hans Brandstetter, Douglas A. Whittington, Pär Nordlund, Stephen J. Lippard*, Christin A. Frederick

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

150 Scopus citations

Abstract

The crystal structure of the nonheme iron-containing hydroxylase component of methane monooxygenase hydroxylase (MMOH) from Methylococcus capsulatus (Bath) has been solved in two crystal forms, one of which was refined to 1.7 Å resolution. The enzyme is composed of two copies each of three subunits (α2β2γ2), and all three subunits are almost completely α-helical, with the exception of two β hairpin structures in the (α subunit. The active site of each (α subunit contains one dinuclear iron center, housed in a four-helix bundle. The two iron atoms are octahedrally coordinated by 2 histidine and 4 glutamic acid residues as well as by a bridging hydroxide ion, a terminal water molecule, and at 4°C, a bridging acetate ion, which is replaced at -160°C with a bridging water molecule. Comparison of the results for two crystal forms demonstrates overall conservation and relative orientation of the domain structures. The most prominent structural difference identified between the two crystal forms is in an altered side chain conformation for Leu 110 at the active site cavity. We suggest that this residue serves as one component of a hydrophobic gate controlling access of substrates to and products from the active site. The leucine gate may be responsible for the effect of the B protein component on the reactivity of the reduced hydroxylase with dioxygen. A potential reductase binding site has been assigned based on an analysis of crystal packing in the two forms and corroborated by inhibition studies with a synthetic peptide corresponding to the proposed docking position.

Original languageEnglish (US)
Pages (from-to)141-152
Number of pages12
JournalProteins: Structure, Function and Genetics
Volume29
Issue number2
DOIs
StatePublished - 1997

Keywords

  • Dinuclear iron center
  • Leucine gate
  • Nonheme iron enzyme
  • Protein crystallography
  • Reductase binding site

ASJC Scopus subject areas

  • Structural Biology
  • Biochemistry
  • Molecular Biology

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