title: Structural and Biochemical Characterization of AidC, a Quorum-Quenching Lactonase with Atypical Selectivity.
abstract: 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 kcat/KM 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 KM 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. Implications for the catalytic mechanism of AHL lactonases are discussed.
authors.affiliation: §Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, Illinois 60660, United States.
authors.forename: Romila
authors.initials: R
authors.lastname: Mascarenhas
authors.forename: Pei W
authors.initials: PW
authors.lastname: Thomas
authors.affiliation: ∥Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, United States.
authors.forename: Chun-Xiang
authors.initials: CX
authors.lastname: Wu
authors.affiliation: ⊥Structural Biology Center, Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
authors.forename: Boguslaw P
authors.initials: BP
authors.lastname: Nocek
authors.affiliation: ∥Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202, United States.
authors.forename: Quyen Q
authors.initials: QQ
authors.lastname: Hoang
authors.affiliation: §Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, Illinois 60660, United States.
authors.forename: Dali
authors.initials: D
authors.lastname: Liu
authors.forename: Walter
authors.initials: W
authors.lastname: Fast
mesh_terms: D002265:Carboxylic Ester Hydrolases / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D045247:Chryseobacterium / Q000737:chemistry / Q000201:enzymology* / Q000502:physiology; D018360:Crystallography, X-Ray; D008958:Models, Molecular; D011487:Protein Conformation; D055503:Protein Multimerization; D053038:Quorum Sensing; D013379:Substrate Specificity
chemical_list: D002265:Carboxylic Ester Hydrolases; C432003:N-acyl homoserine lactonase