Molecular properties of RmlT, a wall teichoic acid rhamnosyltransferase that modulates virulence inListeria monocytogenes

Abstract

Wall teichoic acids (WTA) from the major Gram-positive foodborne pathogenListeria monocytogenesare peptidoglycan-associated glycopolymers decorated by monosaccharides that, while not essential for bacterial growth, are required for bacterial virulence and resistance. Here we report the first structure and function of a bacterial WTA rhamnosyltransferase, RmlT, strictly required forL. monocytogenesWTA rhamnosylation. We demonstrated that RmlT transfers rhamnose from TDP-rhamnose to naked WTA, and that specificity towards TDP-rhamnose is kinetically determined. We solved the RmlT structure, identified key residues for its activity and showed that RmlT behaves as a dimer whose interface is important for its stability and function. We propose that RmlT undergoes a transition between an open and closed conformation, allowing RmlT to first bind WTA and then trapping it inside the tunnel formed by the catalytic, oligomerization and helical subdomains. Finally, we proved that mutation of a single residue in the RmlT active site leads to enzyme inactivation and decreased infectionin vivo, confirming WTA glycosyltransferases as promising targets for next-generation strategies against Gram-positive pathogens.