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Publication Abstract from PubMed

Lytic polysaccharide monooxygenases (LPMOs) are a class of copper-dependent enzymes discovered within the last ten years. They oxidatively cleave polysaccharides (chitin, lignocellulose, hemicellulose and starch-derived), presumably making recalcitrant substrates accessible to glycoside hydrolases. Recently, the first crystal structure of an LPMO-substrate complex was reported, giving insights into the interaction of LPMOs with beta-linked substrates (Frandsen et al., 2016). The LPMOs acting on alpha-linked glycosidic bonds (family AA13) display binding surfaces that are quite different from those of LPMOs that act on beta-linked glycosidic bonds (families AA9-AA11), as revealed from the first determined structure (Lo Leggio et al., 2015), and thus presumably the AA13s interact with their substrate in a distinct fashion. Here, several new structures of the same AA13 enzyme, Aspergillus oryzae AA13, are presented. Crystals obtained in the presence of high zinc-ion concentrations were used, as they can be obtained more reproducibly than those used to refine the deposited copper-containing structure. One structure with an ordered zinc-bound active site was solved at 1.65 A resolution, and three structures from crystals soaked with maltooligosaccharides in solutions devoid of zinc ions were solved at resolutions of up to 1.10 A. Despite similar unit-cell parameters, small rearrangements in the crystal packing occur when the crystals are depleted of zinc ions, resulting in a more occluded substrate-binding surface. In two of the three structures maltooligosaccharide ligands are bound, but not at the active site. Two of the structures presented show a His-ligand conformation that is incompatible with metal-ion binding. In one of these structures this conformation is the principal one (80% occupancy), giving a rare atomic resolution view of a substantially misfolded enzyme that is presumably rendered inactive.

Learning from oligosaccharide soaks of crystals of an AA13 lytic polysaccharide monooxygenase: crystal packing, ligand binding and active-site disorder.,Frandsen KE, Poulsen JC, Tovborg M, Johansen KS, Lo Leggio L Acta Crystallogr D Struct Biol. 2017 Jan 1;73(Pt 1):64-76. doi:, 10.1107/S2059798316019641. Epub 2017 Jan 1. PMID:28045386^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.