The quorum-quenching lactonase from Geobacillus caldoxylosilyticus: purification， characterization， crystallization and crystallographic analysis.

Lactonases are enzymes that are capable of hydrolyzing various lactones such as aliphatic lactones or acyl-homoserine lactones (AHLs)， with the latter being used as chemical signaling molecules by numerous Gram-negative bacteria. Lactonases therefore have the ability to quench the chemical communication， also known as quorum sensing， of numerous bacteria， and in particular to inhibit behaviors that are regulated by this system， such as the expression of virulence factors or the production of biofilms. A novel representative from the metallo-β-lactamase superfamily， dubbed GcL， was isolated from the thermophilic bacterium Geobacillus caldoxylosilyticus. Because of its thermophilic origin， GcL may constitute an interesting candidate for the development of biocontrol agents. Here， we show that GcL is a thermostable enzyme with a half-life at 75°C of 152.5 ± 10 min. Remarkably， it is also shown that GcL is among the most active lactonases characterized to date， with catalytic efficiencies (kcat/Km) against AHLs of greater than 10  M(-1) s(-1). The structure of GcL is expected to shed light on the catalytic mechanism of the enzyme and the molecular determinants for the substrate specificity in this class of lactonases. Here， the expression， purification， characterization， crystallization and X-ray diffraction data collection to 1.6 Å resolution of GcL are reported.