Overall structure and active site of AidH. (a) Top and side views of the AidH monomer. Cartoon representation of AidH with the α/β-hydrolase fold core domain and the cap domain shown in aquamarine and violet/purple, respectively. Secondary-structure elements and catalytic triad residues are labelled in black and red, respectively. (b) Wall-eyed stereo presentation of the active site of AidH. The active site of AidH is the conserved serine protease-type catalytic triad: Ser102, His248 and Glu219. C atoms of the catalytic triad residues and other residues are shown in marine and pale cyan, respectively. O atoms and N atoms are shown in red and deep blue, respectively. Hydrogen bonds are depicted as black short-dashed lines. Interatomic distances are shown in Å.