Lytic polysaccharide monooxygenases have attracted vast attention due to their abilities to disrupt glycosidic bonds via oxidation instead of hydrolysis and to enhance enzymatic digestion of recalcitrant substrates including chitin and cellulose. We have determined high resolution X-ray crystal structures of an enzyme from Neurospora crassa in the resting state and of a copper(II)–dioxo intermediate complex formed in the absence of substrate. X-ray crystal structures also revealed “pre-bound” molecular oxygen adjacent to the active site. An examination of protonation states enabled by neutron crystallography and density functional theory calculations identified a role for a conserved histidine in promoting oxygen activation. These results provide a new structural description of oxygen activation by substrate free lytic polysaccharide monooxygenases and provide insights that can be extended to reactivity in the enzyme–substrate complex.

Background:In cyanobacteria, light harvesting and photosynthesis occur in the thylakoid membranes. Results:The distances between thylakoid membranes are correlated with the size of the phycobilisome antenna and change reversibly and rapidly upon illumination. Conclusion: Thylakoid membranes have a structural plasticity tied to the regulation of photosynthesis. Significance: Characterizing the structural changes in photosynthetic membranes is crucial for understanding light harvesting and photosynthetic productivity.

Neutron protein crystallography is a powerful tool for investigating protein chemistry because it directly locates hydrogen atom positions in a protein structure. The visibility of hydrogen and deuterium atoms arises from the strong interaction of neutrons with the nuclei of these isotopes. Positions can be unambiguously assigned from diffraction at resolutions typical of protein crystals. Neutrons have the additional benefit to structural biology of not inducing radiation damage in protein crystals. The same crystal could be measured multiple times for parametric studies. Here, we review the basic principles of neutron protein crystallography. The information that can be gained from a neutron structure is presented in balance with practical considerations. Methods to produce isotopically-substituted proteins and to grow large crystals are provided in the context of neutron structures reported in the literature. Available instruments for data collection and software for data processing and structure refinement are described along with technique-specific strategies including joint X-ray/neutron structure refinement. Examples are given to illustrate, ultimately, the unique scientific value of neutron protein crystal structures.