4alq
X-Ray photoreduction of Polysaccharide monooxygenase CBM33
Structural highlights
FunctionLCHMO_ENTFA Involved in chitin degradation. Catalyzes the oxidative cleavage of glycosidic bonds in both alpha- and beta-chitin via a copper-dependent mechanism, leading to oxidized chitooligosaccharides with a dominance of even-numbered products. Acts synergistically with the chitinase EfChi18A, and combining the two enzymes leads to rapid and complete depolymerization of crystalline chitin, especially with beta-chitin as a substrate. Is likely involved in a chitin degradation pathway that allows E.faecalis V583 to grow on chitin as a carbon source.[1] Publication Abstract from PubMedLytic polysaccharide monooxygenases (LPMOs) are a recently discovered class of enzymes that employ a copper-mediated, oxidative mechanism to cleave glycosidic bonds. The LPMO catalytic mechanism likely requires that molecular oxygen first binds to Cu(I), but the oxidation state in many reported LPMO structures is ambiguous, and the changes in the LPMO active site required to accommodate both oxidation states of copper have not been fully elucidated. Here, a helical X-ray diffraction method with minimal X-ray dose was used to solve the crystal structure of a chitin-specific LPMO from Enterococcus faecalis (EfaCBM33A) in the Cu(II)-bound form. Subsequently, the crystal was X-ray photo-reduced, which revealed structural changes associated with the conversion from the initial Cu(II)-oxidized form with two coordinated water molecules, which adopts a trigonal bipyramidal geometry, to a reduced Cu(I) form in a T-shaped geometry with no coordinated water molecules. A comprehensive survey of Cu(II) and Cu(I) structures in the Cambridge Structural Database unambiguously shows that the geometries observed in the least and most reduced structures reflect binding of Cu(II) and Cu(I), respectively. Quantum mechanical calculations of the oxidized and reduced active sites reveal little change in the electronic structure of the active site measured by the active site partial charges. Together with a previous theoretical investigation of a fungal LPMO, this suggests significant functional plasticity in LPMO active sites. Overall, this study provides molecular snapshots along the reduction process to activate the LPMO catalytic machinery, and provides a general method for solving LPMO structures in both copper oxidation states. Structural and electronic snapshots during the transition from a Cu(II) to Cu(I) metal center of a lytic polysaccharide monooxygenase by X-ray photo-reduction.,Gudmundsson M, Kim S, Wu M, Ishida T, Haddad Momeni M, Vaaje-Kolstad G, Lundberg D, Royant A, Stahlberg J, Eijsink VG, Beckham GT, Sandgren M J Biol Chem. 2014 May 14. pii: jbc.M114.563494. PMID:24828494[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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