INSIGHTS INTO THE BINDING AND CATALYTIC MECHANISMS OF BACILLUS THURINGIENSIS LACTONASE AND INTERACTIONS OF A PTEN-BINDING INHIBITORY PEPTIDE

The lactonase enzyme (AiiA) produced by Bacillus thuringiensis (B. thuringiensis) serves to degrade autoinducer-1 (AI-1) signaling molecules in what is an evolved mechanism by which allows B. thuringiensis to better compete with other bacteria. Bioassays have been previously performed to determine whether the AI-1 aliphatic tail lengths have any effect on AiiA’s bioactivity; however, data to date are conflicting. To investigate these questions, multiple molecular dynamics simulations were performed across a family of seven acylated homoserine lactones (AHL) along with their associated intermediate and product states. Distance analyses and interaction energy analyses were performed to investigate current bioassay data. Our simulations are consistent with experimental studies showing that AiiA degrades AHLs in a tail length independent manner. Also, a proposed putative oxyanion hole function of Y194 toward the substrate is not observed in any of the reactant or product state simulation trajectories. However, Y194 does seem to show efficacy in stabilizing the intermediate state. Last, we argue through ionization state analyses, that proton-shuttling necessary for catalytic activity is possibly mediated by both water- and substrate-based, intra-molecular proton transfer. Based on this argument, an alternate catalytic mechanism is proposed. Drug dependence, or addiction ultimately described as the maladaptation of a neurochemical reward pathway that is normally used to reinforce behaviors that promote an organism’s survival and/or propagation (e.g., high calorie food seeking and sexual drive). These pathways are mediated via dopaminergic VTA-NAc neuronal networks. The molecular basis for this interaction has been shown to rely on a 5HT-2cR:PTEN interaction via the 3L4F-F1 fragment. The nature of the interaction is unknown. In this work a series of REMD runs are designed to generate candidate conformations that might exist under physiological conditions. These candidates are then subjected to exhaustive six-dimensional, coarse-grained docking simulations against the PTEN protein to produce a myriad of potential docking sites. From these dockings the top scoring poses are observed to point to a single binding site that in turn lend themselves to spectroscopic validation.