The homology model of AmpC and β-lactamase assays of recombinant AmpCs. The model was generated using the A. baumannii ADC-1 (PDB entry 4net) as the template and the identified phosphosites were structurally mapped. A, The cartoon representation of the overall structure shows the predicted relative positions of each phosphosite (white sticks). The phosphosites Ser-88 and Ser-90 are both located in the motif S88VS90K91 (yellow) of domain 2 (magenta). Ser-81 and Thr-151 are located close to the surface of domain 1 (green) and in the P2-loop (cyan), respectively. B, The relative β-lactamase activity of recombinant AmpCs (WT, S90A, and S90D) in the presence or absence of alkaline phosphatase. The data are presented as the means with error bars based on experiments carried out in triplicate. The values were all normalized to that of phosphatase-untreated AmpC-WT. Asterisks (*) indicate statistical significance (p < 0.05).