Quorum quenching lactonases are enzymes capable of hydrolyzing lactones, including N-acyl homoserine lactones (AHLs). AHLs are molecules known as signals in bacterial communication dubbed quorum sensing. Bacterial signal disruption by lactonases was previously reported to inhibit behavior regulated by quorum sensing, such as the expression of virulence factors and the formation of biofilms. Herein, we report the enzymatic and structural characterization of a novel lactonase representative from the metallo-β-lactamase superfamily, dubbed GcL. GcL is a broad spectrum and highly proficient lactonase, with kcat/KM values in the range of 104 to 106 m−1 s−1. Analysis of free GcL structures and in complex with AHL substrates of different acyl chain length, namely, C4-AHL and 3-oxo-C12-AHL, allowed their respective binding modes to be elucidated. Structures reveal three subsites in the binding crevice: 1) the small subsite where chemistry is performed on the lactone ring; 2) a hydrophobic ring that accommodates the amide group of AHLs and small acyl chains; and 3) the outer, hydrophilic subsite that extends to the protein surface. Unexpectedly, the absence of structural accommodation for long substrate acyl chains seems to relate to the broad substrate specificity of the enzyme.
Bibliographical noteFunding Information:
This work was supported by the MnDrive Initiative, and BARD grant IS-4960-16 FR to M.E. This work was also prepared by M.E. using federal funds under award NA18OAR4170101 from Minnesota Sea Grant, National Sea Grant College Program, National Oceanic and Atmospheric Administration, U.S. Department of Commerce. The statements, findings, conclusions, and recommendations are those of the authors and do not necessarily reflect the views of NOAA, the Sea Grant College Program or the U.S. Department of Commerce. This paper is journal reprint no. JR659 of the Minnesota Sea Grant College Program. We thank the Advanced Photon Source and beamline staff for access and support (23 ID-B and 23 ID-D).
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- bacterial signals
- quorum quenching
- quorum sensing
- structure elucidation