BMB Section Seminar: "How oxidative carbohydrate cleaving enzymes orients and locates their spot on crystalline substrate"
Dr. Åsmund Kjendseth Røhr, Groupleader at Department of Chemistry, Biotechnology, and Food Science, Norwegian University of Life Sciences, Norway
Enzyme (green) -crystalline carbohydrate (red) complex
Numerous bacteria and fungi secrete a battery of enzymes when degrading recalcitrant polysaccharides as cellulose and chitin. The copper and oxygen dependent enzymes named lytic polysaccharide monooxygenases (LPMOs) are part of this machinery, cleaving carbohydrate chains that are densely packed and unavailable for the other enzymes involved.
The chitin-active SmLPMO10A (CBP21) has for years served as a workhorse in the LPMO field, and with all the accumulated experimental data it is an excellent model for understanding LPMO-substrate interactions. Here we present data derived from biochemical, spectroscopic, and molecular modeling studies, and relate those to previous work with the aim to construct models for enzyme-substrate complexes.
With EPR spectroscopy we show that SmLPMO10A binds to substrate hexamer, α- and β-chitin in a similar fashion, and the change in the EPR spectra upon substrate binding can be explained by alteration of Cu(II) water coordination. The molecular dynamics simulations show that the enzyme binds to the planer β-chitin surface and to both  and  α-chitin crystal planes in a similar fashion. In agreement with previously published mutational and NMR spectroscopic work (1,2), the conserved residues at the SmLPMO10A substrate binding surface do play individual roles when binding chitin. We also observe that the orientation and geometry of the copper site in our models is consistent with C1-oxidzing activity and that this orientation is maintained after hundreds of nanoseconds of simulations. To conclude we report experimentally supported models of LPMO-crystalline substrate complexes, and we hypothesize that our observations are transferable to other chitin-active LPMOs and also to the cellulose-active enzymes.
 Vaaje-Kolstad, G. et al. J Biol Chem 280, 11313-11319 (2005)
 Aachmann, F.L. et al. PNAS 109 18779-18784 (2012)