Changes in Active Site Loop Conformation Relate to the Transition toward a Novel Enzymatic Activity.

Enzymatic promiscuity, the ability of enzymes to catalyze multiple, distinct chemical reactions, has been well documented and is hypothesized to be a major driver of the emergence of new enzymatic functions. Yet, the molecular mechanisms involved in the transition from one activity to another remain debated and elusive. Here, we evaluated the redesign of the active site binding cleft of lactonase SsoPox using structure-based design and combinatorial libraries. We created variants with largely improved catalytic abilities against phosphotriesters, the best ones being >1000-fold better compared to the wild-type enzyme. The observed shifts in activity specificity are large, and some variants completely lost their initial activity. The selected combinations of mutations have considerably reshaped the active site cavity via side chain changes but mostly through large rearrangements of the active site loops and changes to their conformations, as revealed by a suite of crystal structures. This suggests that a specific active site loop configuration is critical to the lactonase activity. Interestingly, analysis of high-resolution structures hints at the potential role of conformational sampling and its directionality in defining the enzyme activity profile.

Disrupting quorum sensing as a strategy to inhibit bacterial virulence in human, animal, and plant pathogens.

The development of sustainable alternatives to conventional antimicrobials is needed to address bacterial virulence while avoiding selecting resistant strains in a variety of fields, including human, animal, and plant health. Quorum sensing (QS), a bacterial communication system involved in noxious bacterial phenotypes such as virulence, motility, and biofilm formation, is of utmost interest. In this study, we harnessed the potential of the lactonase SsoPox to disrupt QS of human, fish, and plant pathogens. Lactonase treatment significantly alters phenotypes including biofilm formation, motility, and infection capacity. In plant pathogens, SsoPox decreased the production of plant cell wall degrading enzymes in Pectobacterium carotovorum and reduced the maceration of onions infected by Burkholderia glumae. In human pathogens, lactonase treatment significantly reduced biofilm formation in Acinetobacter baumannii, Burkholderia cepacia, and Pseudomonas aeruginosa, with the cytotoxicity of the latter being reduced by SsoPox treatment. In fish pathogens, lactonase treatment inhibited biofilm formation and bioluminescence in Vibrio harveyi and affected QS regulation in Aeromonas salmonicida. QS inhibition can thus be used to largely impact the virulence of bacterial pathogens and would constitute a global and sustainable approach for public, crop, and livestock health in line with the expectations of the One Health initiative.

Changes in Active Site Loop Conformation Relate to the Transition toward a Novel Enzymatic Activity.

Enzymatic promiscuity, the ability of enzymes to catalyze multiple, distinct chemical reactions, has been well documented and is hypothesized to be a major driver for the emergence of new enzymatic functions. Yet, the molecular mechanisms involved in the transition from one activity to another remain debated and elusive. Here, we evaluated the redesign of the active site binding cleft of the lactonase SsoPox using structure-based design and combinatorial libraries. We created variants with largely improved catalytic abilities against phosphotriesters, the best ones being > 1,000-fold better compared to the wild-type enzyme. The observed shifts in activity specificity are large, ~1,000,000-fold and beyond, since some variants completely lost their initial activity. The selected combinations of mutations have considerably reshaped the active site cavity via side chain changes but mostly through large rearrangements of the active site loops, as revealed by a suite of crystal structures. This suggests that specific active site loop configuration is critical to the lactonase activity. Interestingly, analysis of high-resolution structures hints at the potential role of conformational sampling and its directionality in defining an enzyme activity profile.

Applying molecular and phenotypic screening assays to identify efficient quorum quenching lactonases.

Quorum sensing (QS) is a molecular communication system used by microorganisms to adopt behaviors in a cell density-dependent manner. Lactonase enzymes, able to hydrolyze the signal molecules acyl-homoserine lactones (AHL) can counteract QS-mediated virulence in Gram-negative bacteria. Optimizing lactonases activity or specificity for AHL through enzyme engineering approaches is thus highly attractive to increase protective effect. However, only a limited number of screening methods have been developed to handle and evaluate AHL-degrading enzyme libraries. Here, a series of screening procedures were developed to identify improved lactonases using two previously reported enzymes as benchmarks, namely SsoPox and GcL. Specifically, molecular screenings using six different AHL and based on two reporter strains; i.e., Chromobacterium violaceum CV026 and Pseudomonas putida KS35, are reported. In addition, three phenotype-based screenings aiming to evaluate the ability of enzymes to quench a particular QS-related behavior are reported, using C. violaceum, Pseudomonas aeruginosa and Vibrio harveyi as pathogenic type strains. These assays were used to screen a small-sized library and allowed for the identification of various improved variants. To confirm that these variants were real "hits", four of them were produced and purified. Their kinetic parameters against AHL substrates were found to be increased by 2-44.5 -fold as compared to the starting enzyme. Moreover, their increased activity was confirmed by measuring their ability to quench QS in different bacterial systems. These new assays will facilitate the screening of enzyme libraries and will pave the way for the development of proficient engineered QS-disrupting enzymes.

Engineering acyl-homoserine lactone-interfering enzymes toward bacterial control.

Enzymes able to degrade or modify acyl-homoserine lactones (AHLs) have drawn considerable interest for their ability to interfere with the bacterial communication process referred to as quorum sensing. Many proteobacteria use AHL to coordinate virulence and biofilm formation in a cell density-dependent manner; thus, AHL-interfering enzymes constitute new promising antimicrobial candidates. Among these, lactonases and acylases have been particularly studied. These enzymes have been isolated from various bacterial, archaeal, or eukaryotic organisms and have been evaluated for their ability to control several pathogens. Engineering studies on these enzymes were carried out and successfully modulated their capacity to interact with specific AHL, increase their catalytic activity and stability, or enhance their biotechnological potential. In this review, special attention is paid to the screening, engineering, and applications of AHL-modifying enzymes. Prospects and future opportunities are also discussed with a view to developing potent candidates for bacterial control.