1. ^{& ast;}Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
2. ^{& dagger;}Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School and Dana Farber Cancer Institute, Boston, Massachusetts 02115, USA
3. ^{& sect;}Department of Molecular Biology, Stockholm University, S-10691 Stockholm, Sweden
4. ^{& Dagger;}To whom correspondence should be addressed.

Abstract

The 2.2 & Aring; crystal structure of the 251K ₂₂₂ dimeric hydroxylase protein of methane mono-oxygenase from Methylococcus capsulatus (Bath) reveals the geometry of the catalytic di-iron core. The two iron atoms are bridged by exogenous hydroxide and acetate ligands and further coordinated by four glutamate residues, two histidine residues and a water molecule. The dinuclear iron centre lies in a hydrophobic active-site cavity for binding methane. An extended canyon runs between pairs, which have many long -helices, for possible docking of the reductase and coupling proteins required for catalysis.