Oxidative cleavage of glycosidic bonds. Neutron and X-ray crystallography reveal structural details of the enzymatic action of lytic polysaccharide monooxygenase (green and yellow ribbon diagrams) as it breaks polysaccharide chains (gold). This activity enhances the enzymatic hydrolysis of recalcitrant carbohydrate biomass, such as cellulose or chitin. [From O’Dell, W. B., P. K. Agarwal, and F. Meilleur. 2017. “Oxygen Activation at the Active Site of a Fungal Lytic Polysaccharide Monooxygenase.” Angew. Chem. Int. Ed. 56, 767–770. DOI: 10.1002/anie.201610502. © 2017 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim.]
Neutron macromolecular crystallography (NMC) provides information about the location of critical hydrogen atoms in protein crystals at atomic resolution. The technique is complementary to X-ray crystallography, which can determine the three-dimensional positioning of other elements in biological macromolecules but not hydrogen. The X-ray photons used in X-ray crystallography interact with the atomic electric field proportional to atomic number, making hydrogen all but invisible to X-rays. In contrast, the neutrons used in NMC interact with atomic nuclei, making it possible to observe hydrogen and deuterium (heavy hydrogen) and distinguish these from heavier elements such as carbon, nitrogen, and oxygen. This feature of NMC enables studies of hydrogen bonding networks and the protonation states of catalytic residues. In addition, neutrons do not cause radiation damage as is often the case with methods that utilize X-rays or electrons. NMC does, however, require significantly larger crystal volumes than X-ray techniques.
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