A novel ALDH dimer, which mimics the classic ALDH tetramer. (A) The LsALDH16 dimer viewed down the 2-fold axis. In the top part, the two chains have different colors. In the bottom part, the protein is color-coded by domains as in Fig. 3A: NAD+-binding, cyan; catalytic, deep salmon; and C-terminal domain, lime. (B) Close-up view of the intermolecular anti-parallel β-sheet formed by the β-flaps of the C-terminal domains. The two chains have different colors in the inset. (C) The classic ALDH tetramer, as exemplified by ALDH2, viewed down a 2-fold axis (PDB ID 1O00). On the left, the protein is colored by domains as in Fig. 1: NAD+-binding, cyan; catalytic, deep salmon; and oligomerization, blue. The inset shows a close-up view of the intermolecular anti-parallel β-sheet formed by the oligomerization domains of chains B and C. An identical interaction is formed by chains A and D.