Structural Studies of the Cpx Pathway Activator NlpE on the Outer Membrane of Escherichia coli

Abstract

NlpE, an outer membrane lipoprotein, functions during envelope stress responses in Gram-negative bacteria. In Escherichia coli, adhesion to abiotic surfaces has been reported to activate the Cpx pathway in an NlpE-dependent manner. External copper ions are also thought to activate the Cpx pathway mediated by NlpE. We determined the crystal structure of NlpE from E. coli at 2.6 A resolution. The structure showed that NlpE consists of two beta barrel domains. The N-terminal domain resembles the bacterial lipocalin Blc, and the C-terminal domain has an oligonucleotide/oligosaccharide-binding (OB) fold. From both biochemical analyses and the crystal structure, it can be deduced that the cysteine residues in the CXXC motif may be chemically active. Furthermore, two monomers in the asymmetric unit form an unusual 3D domain-swapped dimer. These findings indicate that tertiary and/or quaternary structural instability may be responsible for Cpx pathway activation.

<i>Salmonella enterica</i> <b>serovar Typhi</b> <i>cutF</i> <b>is upregulated during environmental stress</b>

“…These findings showed that the S. Typhi cutF disruption did not confer sensitivity to copper as previously reported (Gupta et al, 1995); rather, these observations agree with the view of the S. Typhi cutF functioning as a sensor of extracellular stresses (Snyder et al, 1995;Hirano et al, 2007). In fact, the mutant strain used by Gupta et al (1995) for identifying the cutF gene from E. coli was a double mutant with mutations in both the cutC and cutF genes, suggesting that increased copper sensitivity observed in the double mutant strain was probably due to its inability to sense and mount a reaction towards the stress from copper toxicity.…”

Antimicrobial Peptides Activate the Rcs Regulon through the Outer Membrane Lipoprotein RcsF

“…7). RcsC, RcsD, and IgaA all have signif- (25). Therefore, either direct interaction of RcsF with the periplasmic domains of RcsC or RcsD or binding to IgaA and release of inhibition could result in activation.…”

MzrA-EnvZ Interactions in the Periplasm Influence the EnvZ/OmpR Two-Component Regulon

“…It was hypothesized that in its extended conformation, the 216-residue-long mature NlpE protein can interact directly with the CpxA sensor kinase (17). The same authors also offered a possibility of CpxA activation through an indirect mechanism involving unfolded NlpE-mediated sequestration of CpxP from CpxA (17).…”