Esterases are hydrolases that catalyze the cleavage, formation, or transesterification of
short-chain fatty acid esters. Common features of esterases are the a/b-hydrolase fold and
the G-X-S-X-G consensus motif around the active site serine, where X denotes any amino
acid. The active site of serine hydrolases contains a catalytic triad composed of a
nucleophilic serine, an amino acid with a catalytic carboxyl group (aspartate or glutamate)
and a histidine. An additional common structural feature is the so-called oxyanion hole which
stabilizes the tetrahedral intermediate. The catalysis works in a four-step mechanism, shown
in Figure 1-9:
1. Nucleophilic attack of the serine oxygen on the substrate, formation of a tetrahedral
intermediate stabilized by histidine and aspartate
2. Release of the alcohol, formation of an acyl enzyme complex