Fig. 4

Placement of acetoin molecules in the active site of SmBdh and its intramolecular interactions. a Placement of R- and S-acetoin molecules in the active site of the WT SmBDH. NAD ⁺ (yellow carbons), R- and S-acetoin molecules (purple and cyan carbons), and side chains of surrounding residues (grey carbons) including Gln247 from the symmetry-related molecule (green carbons) are shown in sticks representation. Hydrogen bonds are depicted as yellow dashed lines. Omit Fo-Fc electron density map at 3σ level is shown as a green mesh over acetoin molecules. b When only R-acetoin is modeled in the active site of the WT SmBDH, a strong peak in the Fo-Fc map appears after refinement (shown as a green mesh at 3σ level) indicating incomplete interpretation of the electron density maps. 2Fo-Fc map contoured at 1σ level is also shown