Amphiphilic peptide Mastoparan‐B induces conformational changes within the AdeB efflux pump, down‐regulates adeB gene expression, and restores antibiotic susceptibility in an MDR strain of Acinetobacter baumannii

Abstract

AbstractMastoparan B (MP‐B) is an amphiphilic peptide with a potent antimicrobial activity against most Gram‐negative bacteria. However, there is little information available on the inhibition of the Acinetobacter baumannii resistance‐nodulation‐cell‐division (RND) efflux pump using this antimicrobial peptide. Here, we carried out a series of in‐silico experiments to find the mechanisms underlying the anti‐efflux activity of MP‐B using a multi‐drug resistant (MDR) strain of A. baumannii (AB). According to our findings, MP‐B demonstrated a potent antibacterial activity against an MDR‐AB (minimum inhibitory concentration [MIC] = 1 μg/mL) followed by a 20‐fold reduction in the adeB gene expression in the presence of sub‐MIC of this peptide. Using Groningen Machine for Chemicals Simulation (GROMACS) via PyMOL Graphical User Interface (GUI), (we observed that, the AdeB transporter had conserved helix‐turn‐helix regions and a tight pore rich in Phe and Ala residues. To understand how inhibition of the AdeB is achieved, we generated 20 apo‐MP‐B poses using the InterPep and SiteMap tools. The high‐quality model was created by homology modeling and used for docking via AutoDock/Vina to identify the MP‐B binding sites. We established that the most apo‐MP‐B formed H‐bonds to the backbone of five amino acids in the Helix‐5. As a result, the dihedral angles of the involved amino acids shift by 9.0–9.6 Ǻ, causing a change in the conformation of the AdeB protein. This led to helix conformation stereoisomerization and block the AdeB activity. MP‐B presumably has dual mechanisms. (1) It blocks the AdeB transporter by changing its conformation. (2) MP‐B influences the adeB gene expression by binding to G‐protein which laterally controls efflux regulators like MarA, RamA, SoxS, and Rob proteins.