(a,b) Model of the AaBioW active site structure during the adenylation (a) and thioester (b) formation steps, generated by superimposing the crystal structures of relevant ligand-bond complexes. Green sticks, nucleotide; purple, pimelate (Pim); yellow, CoA. Active site residues that may play a role in catalysis are shown as tan sticks. (c) Biochemical activities of site-specific variants of active site residues in AaBioW are identified in a and b. The efficiency of each variant is measured as the amount of pimeloyl-CoA formed relative to the wild-type enzyme. Experiments in c were conducted in triplicate. Error bars represent mean ± s.d.