Probing Interactions of PQS Analogs with Outer Membranes of Pseudomonas Aeruginosa Bacteria

Outer membrane vesicles (OMV) released from the outer membrane (OM) of gram-negative bacteria play an undeniable role in their survival by improving signaling process, nutrient acquisition, and antibiotic resistance. Previous studies revealed that Pseudomonas aeruginosa bacterium is incapable of producing OMV without access to the self-secreted Pseudomonas Quinolone Signal (PQS). It has been shown that this signaling molecule can also stimulate OMV formation in other closely related organisms, suggesting small molecule induced OMV biogenesis is a widely conserved process. This work aims to provide fundamental insight into the effect of key functional groups of PQS on its interaction with the bacteria OM by investigating a variety of structural analogs. Using all-atom molecular dynamics, we model the P. aeruginosa OM composed of hexa-acylated PA14 Lipid A in the outer leaflet and a mixture of POPE-POPG phospholipids in the inner leaflet. We probe the membrane interaction with PQS and its analogs, including 2-heptyl-4-quinolone (HHQ), 4-quinolinol, 2-naphthol, and 3-heptyl-2-naphthol to illuminate the role of the third position hydroxy, alkyl side chain, and most importantly the heterocyclic amine. The transmembrane free energy calculations of insertion, as well as hydrogen bonding analyses, show significant differences between these molecules, indicating that all these functional groups have a critical role in the intercalation of PQS into the membrane and hence OMV formation.