High-Resolution XFEL Structure of the Soluble Methane Monooxygenase Hydroxylase Complex with its Regulatory Component at Ambient Temperature in Two Oxidation States

Vivek Srinivas, Rahul Banerjee, Hugo Lebrette, Jason C. Jones, Oskar Aurelius, In Sik Kim, Cindy C. Pham, Sheraz Gul, Kyle D. Sutherlin, Asmit Bhowmick, Juliane John, Esra Bozkurt, Thomas Fransson, Pierre Aller, Agata Butryn, Isabel Bogacz, Philipp Simon, Stephen Keable, Alexander Britz, Kensuke TonoKyung Sook Kim, Sang Youn Park, Sang Jae Lee, Jaehyun Park, Roberto Alonso-Mori, Franklin D. Fuller, Alexander Batyuk, Aaron S. Brewster, Uwe Bergmann, Nicholas K. Sauter, Allen M. Orville, Vittal K. Yachandra, Junko Yano, John D. Lipscomb, Jan Kern, Martin Högbom

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40 Scopus citations


Soluble methane monooxygenase (sMMO) is a multicomponent metalloenzyme that catalyzes the conversion of methane to methanol at ambient temperature using a nonheme, oxygen-bridged dinuclear iron cluster in the active site. Structural changes in the hydroxylase component (sMMOH) containing the diiron cluster caused by complex formation with a regulatory component (MMOB) and by iron reduction are important for the regulation of O2 activation and substrate hydroxylation. Structural studies of metalloenzymes using traditional synchrotron-based X-ray crystallography are often complicated by partial X-ray-induced photoreduction of the metal center, thereby obviating determination of the structure of the enzyme in pure oxidation states. Here, microcrystals of the sMMOH:MMOB complex from Methylosinus trichosporium OB3b were serially exposed to X-ray free electron laser (XFEL) pulses, where the ≤35 fs duration of exposure of an individual crystal yields diffraction data before photoreduction-induced structural changes can manifest. Merging diffraction patterns obtained from thousands of crystals generates radiation damage-free, 1.95 Å resolution crystal structures for the fully oxidized and fully reduced states of the sMMOH:MMOB complex for the first time. The results provide new insight into the manner by which the diiron cluster and the active site environment are reorganized by the regulatory protein component in order to enhance the steps of oxygen activation and methane oxidation. This study also emphasizes the value of XFEL and serial femtosecond crystallography (SFX) methods for investigating the structures of metalloenzymes with radiation sensitive metal active sites.

Original languageEnglish (US)
Pages (from-to)14249-14266
Number of pages18
JournalJournal of the American Chemical Society
Issue number33
StatePublished - Aug 19 2020

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Copyright © 2020 American Chemical Society.


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