*Article* **MexAB-OprM Efflux Pump Interaction with the Peptidoglycan of** *Escherichia coli* **and** *Pseudomonas aeruginosa*

**Miao Ma 1,2,†, Margaux Lustig 1,†, Michèle Salem 1, Dominique Mengin-Lecreulx 3, Gilles Phan 1 and Isabelle Broutin 1,\***


**Abstract:** One of the major families of membrane proteins found in prokaryote genome corresponds to the transporters. Among them, the resistance-nodulation-cell division (RND) transporters are highly studied, as being responsible for one of the most problematic mechanisms used by bacteria to resist to antibiotics, i.e., the active efflux of drugs. In Gram-negative bacteria, these proteins are inserted in the inner membrane and form a tripartite assembly with an outer membrane factor and a periplasmic linker in order to cross the two membranes to expulse molecules outside of the cell. A lot of information has been collected to understand the functional mechanism of these pumps, especially with AcrAB-TolC from *Escherichia coli*, but one missing piece from all the suggested models is the role of peptidoglycan in the assembly. Here, by pull-down experiments with purified peptidoglycans, we precise the MexAB-OprM interaction with the peptidoglycan from *Escherichia coli* and *Pseudomonas aeruginosa*, highlighting a role of the peptidoglycan in stabilizing the MexA-OprM complex and also differences between the two Gram-negative bacteria peptidoglycans.

**Keywords:** membrane; peptidoglycan; efflux pump assembly; resistance; *Pseudomonas*
