An Undecaprenyl Phosphate-Aminoarabinose Flippase Required for Polymyxin Resistance in Escherichia coli

Abstract

Modification of lipid A with the 4-amino-4-deoxy-L-arabinose (L-Ara4N) moiety is required for resistance to polymyxin and cationic antimicrobial peptides in Escherichia coli and Salmonella typhimurium. An operon of seven genes (designated pmrHFIJKLM in S. typhimurium), which is regulated by the PmrA transcription factor and is also present in E. coli, is necessary for the maintenance of polymyxin resistance. We previously elucidated the roles of pmrHFIJK in the biosynthesis and attachment of L-Ara4N to lipid A and renamed these genes arn-BCADT, respectively. We now propose functions for the last two genes of the operon, pmrL and pmrM. Chromosomal inactivation of each of these genes in an E. coli pmrA c parent switched its phenotype from polymyxin-resistant to polymyxin-sensitive. The lipid A moiety of lipopolysaccharide (LPS) 4 in the outer membranes of Gram-negative bacteria typically consists of a ␤,1Ј-6-linked disaccharide of glucosamine, modified with phosphate groups at the 1-and 4Ј-positions, and with R-3-hydroxyacyl chains at the 2-, 3-, 2Ј-, and 3Ј-positions (Fig.

ABC Transporters Involved in Export of Cell Surface Glycoconjugates

“…Examples include the addition of 4-aminoarabinose to LPS lipid A (120) and the phage-encoded modification of O-PSs by glucosylation in species such as Shigella (51,76). ArnE and ArnF, two small proteins of 111 and 128 amino acids, respectively, have been implicated in flipping the Und-P-4-aminoarabinose precursor involved in LPS modification (176). ArnE and ArnF each contain four predicted transmembrane helices and share both topological and sequence similarity with members of the drug/ metabolite transporter superfamily, which includes EmrE from E. coli (176).…”

“…ArnE and ArnF, two small proteins of 111 and 128 amino acids, respectively, have been implicated in flipping the Und-P-4-aminoarabinose precursor involved in LPS modification (176). ArnE and ArnF each contain four predicted transmembrane helices and share both topological and sequence similarity with members of the drug/ metabolite transporter superfamily, which includes EmrE from E. coli (176). GtrA is predicted to function in flipping Und-Plinked precursors required for O-PS modifications in Shigella (51).…”

Bile Salts Induce Resistance to Polymyxin in Enterohemorrhagic Escherichia coliO157:H7

“…The addition of L-Ara4N to lipid A has been shown to confer on Gram-negative bacteria resistance to several cationic antimicrobial peptides (CAMPs), including polymyxin B (PMB), a peptide antibiotic often used to study antimicrobial peptide resistance (19,20,37,38,40,63,67,74). The lipid A modifications, controlled through the BasRS (PmrAB) TCRS, in both E. coli and Salmonella spp.…”

An iron-regulated LysR-type element mediates antimicrobial peptide resistance and virulence in Yersinia pseudotuberculosis

“…The pmrL and pmrM products belong to the drug/metabolite exporter family and have been recently shown to form a heterodimer that transfers the L-4-aminoarabinose linked to the undecaprenyl phosphate of the lipid from the cytoplasmic to the periplasmic side of the inner membrane. In E. coli, pmrL and pmrM inactivation is not enough to abolish L-4-aminoarabinose export to the periplasm (Yan et al, 2007); additional, unidentified drug/metabolite exporters may thus exist. YPTB0331 is predicted to contain 10 membrane-spanning peptide segments and transporterspecific motifs, and thus falls into the MFS, which contains members capable of exporting molecules of various sizes through the inner membrane (Pao et al, 1998).…”