Fungal lytic polysaccharide monooxygenases (LPMOs) are known to enhance the efficiency of cellulose-hydrolyzing enzymes through oxidative cleavage of the glycosidic bonds. For this study, PMO-2 from Neurospora crassa was heterologously expressed from Pichia pastoris, purified, and crystallized for high-resolution X-ray crystal structures that revealed “prebound” molecular oxygen in the resting state and a dioxo species in complex with the catalytic copper (Cu2+) ion, which is the first structural description of molecular oxygen (O2) activation by a LPMO. In addition, neutron diffraction studies and density functional theory calculations have identified a role for a conserved histidine in promoting oxygen activation. Extension of these studies to the enzyme-substrate complex could provide a complete picture of the enzymatic mechanism for the potential benefit of applications such as bioethanol production.
O’Dell, W. B., et al. “Oxygen Activation at the Active Site of a Fungal Lytic Polysaccharide Monooxygenase.” Angew. Chem. Int. Ed.129(3), 785–788 (2017). [DOI:10.1002/anie.201610502].
Instruments and Facilities Used: Neutron crystallography. Joint X-ray/neutron refinement at Center for Structural Molecular Biology at Oak Ridge National Laboratory (ORNL). Diffraction data were collected at SER-CAT 22-ID at the Advanced Photon Source at Argonne National Laboratory and at CG-4D IMAGINE (NSF MRI 09229719) at the High Flux Isotope Reactor at ORNL.