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Figure 4
Lys10*–Thr57* dyad. (a) Stick representation of a portion of the active site highlighting the Lys10*–Thr57* dyad. Difference neutron density calculated in the absence of deuterons bound to Lys10*NZ and Thr57*OG1 is shown at the +3.0σ (green) and +2.0σ (lemon) levels, respectively. No significant peak was observed near Thr57*OG1 at the +3.0σ level. (b) Normalized probability distribution of the Thr57* (CA–CB–OG1–HG1) torsion angle during a 100 ns classical MD simulation. Stick representations highlight the structures at −72° (OG1–HG1 bond pointing toward the triazole ring of 8AZA) and −135° angles (OG1–HG1 bond parallel to the 8AZA plane). The broken magenta line at −110.4° indicates the torsion angle in the final structure. (c) Protonation state in the active site. A strong hydrogen bond is formed between Lys10*DZ1 and Thr57*OG1 (1.97 Å) while Thr57*DG1 is engaged in an O—H⋯π interaction (2.77 Å) with N7 of the 8AZA triazole ring. A chain of water molecules (W2, W3, W4) connects 8AZA to the dyad. His256 is neutral with its hydrogen located on ND1 which is hydrogen bonded to W5. Cyan broken lines represent hydrogen bonds. Residue Asn254 has been omitted for clarity.

ISSN: 2052-2525