Activation of PmrA Inhibits LpxT-dependent Phosphorylation of Lipid A Promoting Resistance to Antimicrobial Peptides

Mol Microbiol. 2010 Jun;76(6):1444-60. doi: 10.1111/j.1365-2958.2010.07150.x. Epub 2010 Apr 1.

Abstract

During its transport to the bacterial surface, the phosphate groups of the lipid A anchor of Escherichia coli and Salmonella lipopolysaccharide are modified by membrane enzymes including ArnT, EptA and LpxT. ArnT and EptA catalyse the periplasmic addition of the positively charged substituents 4-amino-4-deoxy-L-arabinose and phosphoethanolamine respectively. These modifications are controlled by the PmrA transcriptional regulator and confer resistance to cationic antimicrobial peptides, including polymyxin. LpxT, however, catalyses the phosphorylation of lipid A at the 1-position forming 1-diphosphate lipid A increasing the negative charge of the bacterial surface. Here, we report that PmrA is involved in the regulation of LpxT. Interestingly, this regulation does not occur at the level of transcription, but rather following the assembly of LpxT into the inner membrane. PmrA-dependent inhibition of LpxT is required for phosphoethanolamine decoration of lipid A, which is shown here to be critical for E. coli to resist the bactericidal activity of polymyxin. Furthermore, although Salmonella lipid A is more prevalently modified with l-4-aminoarabinose, we demonstrate that loss of Salmonella lpxT greatly increases EptA modification. The current work is an example of the complexities associated with the structural remodelling of Gram-negative lipopolysaccharides promoting bacterial survival.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Anti-Bacterial Agents / pharmacology
  • Bacterial Proteins / metabolism*
  • Drug Resistance, Bacterial
  • Escherichia coli / drug effects
  • Escherichia coli / metabolism
  • Escherichia coli / physiology*
  • Escherichia coli Proteins / metabolism*
  • Gene Deletion
  • Gene Expression Regulation, Bacterial*
  • Lipid A / metabolism*
  • Molecular Structure
  • Phosphorylation
  • Phosphotransferases (Phosphate Group Acceptor) / metabolism*
  • Phosphotransferases / metabolism*
  • Polymyxins / pharmacology*
  • Salmonella typhimurium / drug effects
  • Salmonella typhimurium / metabolism
  • Salmonella typhimurium / physiology*

Substances

  • Anti-Bacterial Agents
  • Bacterial Proteins
  • Escherichia coli Proteins
  • Lipid A
  • Polymyxins
  • pmrA protein, Bacteria
  • Phosphotransferases
  • LpxT protein, E coli
  • Phosphotransferases (Phosphate Group Acceptor)