Frontispiece: Molecular Mechanism of Substrate Oxidation in Lytic Polysaccharide Monooxygenases: Insight from Theoretical Investigations

A frontier-orbital view of the initial steps of lytic polysaccharide monooxygenase reactions

“…We further investigated the effect of H2O2 binding on the electronic structure. H2O2 was added to Cu(I) and Cu(I)-Cell-Cl -, replacing either the equatorial 8,24,75 water or chloride (note that with 4.03 Å and 3.84 Å respective distances to copper, neither the water nor the chloride is in coordination distance). In all structures, coordinates of H2O2 were freely optimized together with the hydrogen atoms, employing the procedure Table 1: Selected distances for the structures shown in Figure 2.…”

“…the structure without substrate) with the procedure described above, we could only obtain a structure reminiscent of the "caged" state (indicated as Cu(II)-HO--OH in Figure 1), where H2O2 coordinates to copper and the O-O distance is elongated to distances of approximately 2 or more Ångström. [8][9][10] The prebound form has previously been calculated with both TPSS and B3LYP using a QM/MM embedding scheme to mimic the protein environment [8][9][10] and it was also obtained by Lim et al 51 who employed a QM-cluster approach. Therefore, we optimized the Cu(I)…H2O2 structure with the same functional (B3LYP) that Lim His1 is the N-terminal residue that binds bidentate through the amine of the N-terminus and the imidazole side chain.…”

“…In the second coordination sphere, we included Gln162 and His147, which are both important in stabilizing the pre-bound H2O2 structures. [8][9][10] If cellotetraose is present, it binds from subsite -2 to +2, and forms a hydrogen bond to the so-called "pocket water" 11 that in turn hydrogen bonds to the terminal NH2 group of His1. Geometrical changes upon reduction and substrate binding are described in the main text and in detail in Ref.…”

“…In the pre-bound state, H2O2 is not coordinated to Cu(I), but instead located in the pocket between the substrate and active site, where it is stabilized by interactions with a second-sphere histidine and glutamine (see His147 and Gln162 in Figure 2). [8][9][10] We observe that substrate binding brings H2O2 closer to copper (Cu-O distance of 2.54 Å and 2.39 Å in Cu(I)…H2O2 and Cu(I)-Cell…H2O2, respectively) and increases the O-O bond in Figure 5: Normalized orbital energies and Löwdin reduced orbital populations per molecular orbital for substrate-free and substrate-bound structures with pre-bound H2O2, obtained from B3LYP/def2-TZVPP calculations (and obtained from adding H2O2 to the crystal structures, see right green boxes in Figure 1). The colour indicates the residue with the largest Löwdin reduced orbital population (see legend).…”

A frontier-orbital view of the initial steps of lytic polysaccharide monooxygenase reactions

“…In the second coordination sphere, we included Gln162 and His147, which are both important in stabilizing the pre-bound H 2 O 2 structures. [40][41][42] If cellotetraose is present, it binds from subsite −2 to +2, and forms a hydrogen bond to the so-called "pocket water" 43 that in turn hydrogen bonds to the terminal NH 2 group of His1. Geometrical changes upon reduction and substrate binding are described in the main text and in detail in ref.…”