Fig. 2

SmBdh functional complex and key structural features. a SmBdh tetramer. Protein chains A, B, A^symm and B^symm are shown in cartoon representation and colored grey, yellow, green and cyan, respectively. NAD⁺ , ADP and acetoin molecules are shown in sticks representation. N- and C-termini of the protein chains are marked. b ‘Open’ and ‘closed’ conformations of SmBdh superimposed. Protein chains are shown in cartoon representation and colored grey except for the loop 180–203 containing helices α6 and α7. ‘Open’ conformation of the loop 180–203 is colored purple and ‘closed’ conformation is colored green. Secondary structure elements are labeled. NAD⁺ and acetoin molecules bound in ‘closed’ conformation are shown in sticks representation. Positions of Cα atoms of Ala93 and Trp192 are shown by arrows. c Zoom-in view of NAD + interaction with the ‘closed’ conformation of SmBdh. Side chains of Thr186, Met188, and Thr189 are shown in sticks representation. H-bonds formed upon NAD ⁺ binding are shown as yellow dashed lines