Fig. 2.

The unique AidB tetramer. (A) Four subunits A, B, C, and D associate with dihedral symmetry as a dimer of dimers. The FAD cofactors at each of the A/B and C/D dimer interfaces are shown as black CPK spheres. N-terminal extensions and L1′2′ loops that form the AB/CD interface unique to AidB are labeled with the letter N and orange stars, respectively. The orientations of the cylinder and surface representations are identical, with the view down one two-fold axis. (B) Variation in subunit organization. MCAD tetramer (Left), AidB tetramer (Center), and ACO dimer (Right) are oriented with respect to the AB dimers (gold and yellow subunits). AidB is rotated 60° about a vertical axis with respect to the orientation in A. The subunits within the CD dimer in the AidB and MCAD tetramers are shaded light and dark gray. C-terminal domains in AidB and ACO are highlighted blue and cyan.