Dynamic Determinants of Quorum Quenching Mechanism Shared among N-terminal Serine Hydrolases

ABSTRACT

Due to the alarming global crisis of the growing microbial antibiotic resistance, investigation of alternative strategies to combat this issue has gained considerable momentum in the recent decade. A quorum quenching (QQ) process disrupts bacterial communication through so-called quorum sensing that enables bacteria to sense the cell density in the surrounding environment. Due to its indirect mode of action, QQ is believed to exert limited pressure on essential bacterial functions and consequently avoid inducing resistance. Although many enzymes are known to display the QQ activity towards various molecules used for bacterial signaling, the in-depth mechanism of their action is not well understood hampering their possible optimization for such exploitation. In this study, we compare the potential of three members of N-terminal serine hydrolases to degrade N-acyl homoserine lactones–signaling compounds employed by Gram-negative bacteria. Using molecular dynamics simulation of free enzymes and their complexes with two signaling molecules of different lengths, followed by quantum mechanics/molecular mechanics molecular dynamics simulation of their initial catalytic steps, we explored molecular details behind their QQ activities. We observed that all three enzymes were able to degrade bacterial signaling molecules following an analogous reaction mechanism. For the two investigated penicillin G acylases from Escherichia coli (ecPGA) and Achromobacter spp. (aPGA), we confirmed their putative activities experimentally hereby extending the set of known quorum quenching enzymes by these representatives of biotechnologically well-optimized enzymes. Interestingly, we detected enzyme- and substrate-depended differences among the three enzymes caused primarily by the distinct structure and dynamics of acyl-binding cavities. As a consequence, the first reaction step catalyzed by ecPGA with a longer substrate exhibited an elevated energy barrier due to a too shallow acyl-binding site incapable of accomodating this molecule in a required configuration. Conversely, unfavorable energetics on both reaction steps were observed for aPGA in complex with both substrates, conditioned primarily by the increased dynamics of the residues gating the entrance to the acyl-binding cavity. Finally, the energy barriers of the second reaction step catalyzed by Pseudomonas aeruginosa acyl-homoserine lactone acylase with both substrates were higher than in the other two enzymes due to distinct positioning of Arg297β. These discovered dynamic determinants constitute valuable guidance for further research towards designing robust QQ agents capable of selectively controlling the virulence of resistant bacteria species.