Simultaneous molecular docking of different ligands to His6-tagged organophosphorus hydrolase as an effective tool for assessing their effect on the enzyme
Authors: Aslanli Aysel , Efremenko Elena 
Published: September 2019

Background
Enzymatic hydrolysis of N-acyl homoserine lactones (AHLs), which are signaling molecules responsible for the development of antibiotic resistance in gram-negative bacteria, is a potential solution to overcoming antibiotic resistance problem. It has been established that hexahistidine-tagged organophosphorus hydrolase (His6-OPH) exhibits lactonase activity against a number of AHLs and that the combined application of His6-OPH with β-lactam antibiotics leads to an increase in the efficiency of the action of both the enzyme and antibiotics. The use of computational methods can be an effective way to search for and select from the known antibiotics to find the most rational “partners” for combining with this enzyme and creating effective antibacterial agents with a dual (lactonase and antibacterial) functional activity.

Methods
In this study, by using AutoDock Vina and Gromacs softwares the molecular docking and the molecular dynamics methods were adopted to simulate models of puromycin, ceftiofur, and/or AHLs docked to the surface of a dimer molecule of His6-OPH and to study their binding properties. GABEDIT and GAMESS-US packages were used to generate and simulate electron densities of docked AHLs.

Results
Interactions of N-butyryl-DL-homoserine lactone (C4-HSL), N-(3-oxooctanoyl)-L-homoserine lactone (C8-HSL) and N-(3-oxododecanoyl)-L-homoserine lactone (C12-HSL) with His6-OPH dimer active sites in the presence of puromycin and ceftiofur were simulated and studied. The possible intersection of long-chain AHLs with antibiotic molecules in the active sites of the enzyme was revealed. The binding energies of antibiotics and AHLs with the His6-OPH surface were estimated. Statistically significant differences (p = 0.003) were observed between the values calculated for both C4-HSL and C12-HSL, whereas there were no statistically significant differences between the values of the other groups (p ≥ 0.100). The binding energies of AHLs with His6-OPH were slightly higher as compared with the binding energies of antibiotics with the enzyme. The dynamics of the most probable models obtained from docking were investigated. RMSD and RMSF analysis of His6-OPH-AHL complexes in the absence and presence of antibiotics were performed. The interaction energy values of antibiotics and AHLs with the His6-OPH were assessed. Significant increase of the AHLs steadiness in enzyme-substrate complexes in the presence of antibiotics was revealed. The interaction between His6-OPH and C12-HSL was established as thermodynamically more favored.

Conclusions
It has been established that the studied antibiotics puromycin and ceftiofur steady the enzyme-substrate complexes, but at the same time lead to a decrease in the long-chain AHL-hydrolytic activity of His6-OPH in such a combination as compared to a native enzyme, and, therefore, it should be taken into account when creating a therapeutic composition based on combining antibiotics with His6-OPH.