Regulation of the permeability of the gonococcal cell envelope by the mtr system

Abstract

The mtrR gene of Neisseria gonorrhoeae controls the level of susceptibility to hydrophobic antibiotics and detergents. The mtrR gene was cloned and shown to encode a putative transcriptional repressor. The mtr region was homologous to the envCD and acrAB regions of Escherichia coli, which are also involved in susceptibility to hydrophobic compounds. A homologous repressor protein was encoded by a previously unrecognized open reading frame within both the envCD and acrAB regions. Deletion of mtrR resulted in increased resistance to antibiotics and detergents: the mtrR mutations in two penicillin-resistant clinical isolates resulted in a change of His-105 to Tyr. We propose that the mtrR repressor allows gonococci to regulate the permeability of its cell envelope in response to environmental signals, so that they can grow in the presence of toxic faecal lipids in the rectum as well as in the genital tract.

Modulation of Neisseria gonorrhoeae susceptibility to vertebrate antibacterial peptides due to a member of the resistance/nodulation/division efflux pump family

“…Using the microtiter well growth inhibition assay described above, we found ( Table 1) that isogenic transformant strains bearing insertionally inactivated mtrC (strain KH12), mtrD (strain KH14), or mtrE (strain RD1) genes were significantly (P ϭ 0.001) more susceptible to PG-1 (MGICs range of 0.2-0.75 g͞ml) than parental strain FA19 (MGIC of 4.37 g͞ml). The extent of enhanced PG-1 susceptibility of these strains was similar to that observed previously for other antimicrobial compounds that are removed from gonococci by the mtr efflux system (14)(15)(16)(17)(18).…”

“…As an additional test of the above hypothesis, we next examined levels of PG-1 susceptibility among isogenic transformant strains bearing mutations in the mtrR gene (14,28), which encodes a transcriptional repressor [MtrR (17)] that regulates transcription of the mtrCDE operon (28). Enhanced resistance of gonococci to HAs can be due to mutations in the mtrR gene, either as a result of a single basepair deletion in its promoter (28) or a missense mutation that causes a radical amino acid change in the helix-turn-helix motif of MtrR that abrogates binding of it to the mtrCDE promoter (29).…”

“…2B). Because the kanamycin-resistance cassette within the mtrD gene, which encodes the membrane transporter As BR54 but mtrD54 † 7.14 (Ϯ2.67) *The construction of transformant strains KH12, KH14, and RD1 has been described (14)(15)(16)(17)(18). Strain BR54 was kindly provided by P. F. Sparling (21).…”

“…It was verified that the MtrC-MtrD-MtrE efflux pump was indeed responsible for PG-1 export by comparing the accumulation of radiolabeled PG-1 (0.25 g͞ml) by isogenic strains FA19 and KH14, which revealed that strain KH14 accumulated at least 50% more PG-1 than parental strain FA19 over a 35-min incubation period (Fig. 4B) The MtrC-MtrD-MtrE efflux pump can recognize a broad range of substrates that includes structurally diverse antibiotics, dyes, and detergents (14)(15)(16)(17)(18). Based on genetic and biochemical results obtained in this study, this list now includes certain antibacterial peptides that can assume ␤-sheet (PG-1) or ␣-helical (PC-8 and LL-37) structures.…”

“…Like the well characterized defensins, protegrins are cationic, cysteine-rich peptides that assume a ␤-structure in solution. However, protegrins are smaller than defensins (16)(17)(18) vs. 29-ϳ40 amino acids, respectively) and have two instead of three intramolecular disulfide bridges (see Fig. 1).…”