Enhanced preference for π-bond containing substrates is correlated to Pro110 in the substrate-binding tunnel of Escherichia coli thioesterase I/protease I/lysophospholipase L1

Escherichia coli thioesterase I/protease I/lysophospholipase L1 (TAP) possesses multifunctional enzyme with thioesterase, esterase, arylesterase, protease, and lysophospholipase activities. Leu109, located at the substrate-binding tunnel, when substituted with proline (Pro) in TAP, shifted the substrate-preference from medium-to-long acyl chains to shorter acyl chains of triglyceride and p-nitrophenyl ester, and increased the preference for aromatic-amino acid-derived esters. In the three-dimensional TAP structures, the only noticeable alteration of backbone and side chain conformation was located at the downstream Pro110–Ala123 region rather than at Pro109 itself. The residue Pro110, adjacent to Leu109 or Pro109, was found to contribute to the substrate preference of TAP enzymes for esters containing acyl groups with π bond(s) or aromatic group(s). Some of the interactions between the enzyme protein and the substrate may be contributed by an attractive force between the Pro110 C–H donor and the substrate π-acceptor.