Droperidol as a potential inhibitor of acyl-homoserine lactone synthase from A. baumannii: insights from virtual screening, MD simulations and MM/PBSA calculations

Acinetobacter baumannii belongs to the ESKAPE family of pathogens and is a multi-drug resistant, gram-negative bacteria which follows the anaerobic form of respiration. A. baumannii is known to be the causative agent of hospital-related infections such as pneumonia, meningitis, endocarditis, septicaemia and a plethora of infections such as urinary tract infections found primarily in immunocompromised patients. These attributes of A. baumannii make it a priority pathogen against which potential therapeutic agents need to be developed. A. baumannii employs the formation of a biofilm to insulate its colonies from the outer environment, which allows it to grow under harsh environmental conditions and develop resistance against various drug molecules. Acyl-homoserine lactone synthase (AHLS) is an enzyme involved in the quorum-sensing pathway in A. baumannii, which is responsible for the synthesis of signal molecules known as acyl-homoserine lactones, which trigger the signalling pathway to regulate the factors involved in biofilm formation and regulation. The present study utilised a homology-modelled structure of AHLS to virtually screen it against the ZINC in trial/FDA-approved drug molecule library to find a subset of potential lead candidates. These molecules were then filtered based on Lipinski's, toxicological and ADME properties, binding affinity, and interaction patterns to delineate lead molecules. Finally, three promising molecules were selected, and their estimated binding affinity values were corroborated using AutoDock 4.2. The identified molecules and a control molecule were subsequently subjected to MD simulations to mimic the physiological conditions of protein ligand-binding interaction under the influence of a GROMOS forcefield. The global and essential dynamics analyses and MM/PBSA based binding free energy computations suggested Droperidol and Cipargamin as potential inhibitors against the binding site of AHLS from A. baumannii. The binding free energy calculations based on the MM/PBSA method showed excellent results for Droperidol (- 50.02 ± 4.67 kcal/mol) and Cipargamin (- 42.29 ± 4.05 kcal/mol).

An extensive computational study to identify potential inhibitors of Acyl-homoserine-lactone synthase from Acinetobacter baumannii (strain AYE)

A member of the ESKAPE family of pathogens, A. baumannii, is an opportunistic gram-negative multidrug-resistant bacterium. A. baumannii is a ubiquitous coccobacillus involved in various hospital-related infections such as wound infections, pneumonia, urinary tract infections, septicaemia, endocarditis and ventilator assisted pneumonia and accounts for approximately 1-2% of all nosocomial bloodstream infections; hence it becomes imperative to identify potential therapeutic agents against the dreadful pathogen. The quorum-sensing pathway becomes an attractive drug target due to its role in biofilm regulation and formation, which provides the bacteria insulation from the harsh environment. A crucial protein in biofilm formation and regulation is Acyl-homoserine-lactone synthase (AHLS), responsible for producing signal molecules that trigger the signalling pathway for biofilm formation and regulation. The current study modeled the three-dimensional structure of AHLS in A. baumannii (strain AYE) followed by high-throughput virtual screening of the enamine-AC small-molecule database to identify lead molecules against its acylated-ACP (Acyl Carrier Protein) substrate-binding site. Based on the estimated binding affinity, estimated inhibition constant, ADME analysis and interaction patterns of the screened molecules, three lead candidates (Z815888654, Z2416029019, Z3766992625) were identified along with a control molecule (J8-C8). These molecules were then subjected to molecular dynamics simulations where the physiological effect of ligand binding on the protein was virtually predicted and analysed. The MM/PBSA based binding free energy calculations showed favourable results for Z815888654 (-22.77 ± 2.94 kcal/mol), Z2416029019 (-33.68 ± 2.63 kcal/mol), Z3766992625 (-21.44 ± 3.40 kcal/mol). The study employed global and essential dynamics analyses, MM/PBSA based binding free energy, free energy landscape and dynamic cross-correlation matrix to suggest Z815888654, Z2416029019 and Z3766992625 as potential inhibitors against the acylated-ACP substrate-binding site in AHLS from A. baumannii.