Multifunctional enzyme thioesterase I/protease I/lysophospholipase L1 of Escherichia coli shows exquisite structure for its substrate preferences

Thioesterase I/protease I/lysophospholipase L1 (EC 3.1.2.2) of Escherichia coli is an enzyme with multiple functions and is abbreviated as TAP due its unique discovery in at least 5 different laboratories since the 1960s. Crystal structural analysis identified essential amino acid residues for the catalytic triad, which are residues Ser10, Asp154 and His157, and the oxyanion hole, which contains residues Ser10, Gly44 and Asn73. Through site-directed mutagenesis, His157 was determined to play a pivotal role in enzyme catalysis through dual functions in the catalytic triad and oxyanion intermediate formation. The study of L109P revealed that its adjacent residue, Pro110, dominates the substrate preference for π-bond containing substrates. The non-active site residue Trp23 interweaves the protein framework and dynamic motions during catalysis through hydrogen bonding and aromatic–aromatic interactions. TAP may be a model enzyme with exquisite structural features that displays subtle characteristics for its substrate preferences.