Structural and Biochemical Characterization of AidC, a Quorum‐Quenching Lactonase With Atypical Selectivity

Quorum‐quenching catalysts are of interest for potential application as biochemical tools for interrogating interbacterial communication pathways, as antibiofouling agents, and as anti‐infective agents in plants and animals. Herein, the structure and function of AidC, an N ‐acyl‐l‐homoserine lactone (AHL) lactonase from Chryseobacterium , is characterized. Steady‐state kinetics show that zinc‐supplemented AidC is the most efficient wild‐type quorum‐quenching enzymes characterized to date, with a k cat / K M value of approximately 2 × 10 6 M −1 s −1 for N ‐heptanoyl‐l‐homoserine lactone. The enzyme has stricter substrate selectivity and significantly lower K M values (ca. 50 μM for preferred substrates) compared to those of typical AHL lactonases (ca. >1 mM). X‐ray crystal structures of AidC alone and with the product N ‐hexanoyl‐l‐homoserine were determined at resolutions of 1.09 and 1.67 Å, respectively. Each structure displays as a dimer, and dimeric oligiomerization was also observed in solution by size‐exclusion chromatography coupled with multiangle light scattering. The structures reveal two atypical features as compared to previously characterized AHL lactonases: a “kinked” α‐helix that forms part of a closed binding pocket that provides affinity and enforces selectivity for AHL substrates and an active‐site His substitution that is usually found in a homologous family of phosphodiesterases. Mutations on this His substitution are being studied along with other suspected catalytic residues. Implications of the catalytic mechanism of AHL lactonases will be discussed based on these data and prior knowledge of other AHL lactonases. Support or Funding Information National Science Foundation, Grant No. CHE‐1308672