Fig. 3.

ObiF1 Adenylation domain structure and MLP interaction. a The MLP domain (purple) interacts with the A domain (yellow) in the adenylate-forming conformation. b Stereorepresentation of the specificity determining residues of the substrate binding pocket of the adenylation domain. Cα positions of two glycine residues are indicated with a sphere. Only a single conformation of the side chain of Trp666 is shown. c β-OH-p-NO₂-homoPhe binds in the A domain active site where the β-hydroxyl forms H-bonds with backbone amide carbonyls of Gly737 and Gly764. Electron density (contoured at 2.5σ) calculated with mF_o–DF_c coefficients from an omit map (ligand occupancy set at zero) generated with simulated annealing. The α-amino group forms a salt-bridging interaction with Asp662 and an H-bond with the amide proton of Thr766. The side chain of Trp666, which adopts two alternate conformations, contributes to the hydrophobic pocket around the p-NO₂-phenyl ring. d Trp1343 and Trp1353 of the MLP domain form a pocket around Ala841 of the A domain. e The MLP domain in relation to the C domain (blue) and A domain active site