# The Esc(1-21)-1c Antimicrobial Peptide Inhibits a Specific Transcriptional Activator of the MexAB–OprM Efflux Pump in P. aeruginosa

## TL;DR

This study identifies how an antimicrobial peptide inhibits a key protein involved in antibiotic resistance in Pseudomonas aeruginosa.

## Contribution

The paper reveals a novel regulatory mechanism of the MexAB–OprM efflux pump via inhibition of Q9I5H3 by the Esc(1-21)-1c peptide.

## Key findings

- Esc(1-21)-1c interacts with Q9I5H3, a homolog of E. coli QseB, in P. aeruginosa.
- The peptide competitively inhibits Q9I5H3's binding to the MexAB–OprM promoter.
- This inhibition is dose-dependent and suggests a new therapeutic target for multidrug-resistant P. aeruginosa.

## Abstract

The emergence of multidrug-resistant Pseudomonas aeruginosa strains is increasingly becoming a critical threat to global health. Among the resistance mechanisms, the MexAB–OprM efflux pump confers P. aeruginosa with an efficient method to export a broad spectrum of antibiotics. The antimicrobial peptide Esc (1-21)-1c was shown to downregulate this efflux system, though its mechanism of action has not been unveiled thus far. Here, we employed a combination of molecular modeling and experimental methods to investigate the precise peptide inhibitory mechanism. Functional proteomic experiments revealed the P. aeruginosa protein Q9I5H3, homologous to E. coli QseB, as a putative key target of Esc(1-21)-1c. Molecular docking predicted stable peptide–protein interactions, which were experimentally validated through fluorescence spectroscopy. Furthermore, electrophoretic mobility shift assays demonstrated that Q9I5H3 specifically binds the MexAB–OprM promoter and that Esc(1-21)-1c competitively inhibits this interaction in a dose-dependent manner. These findings reveal a previously uncharacterized regulatory pathway for efflux pump control and highlight Q9I5H3 as a promising therapeutic target against multidrug-resistant P. aeruginosa.