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J Bacteriol. 2019 Mar 11. pii: JB.00745-18. doi: 10.1128/JB.00745-18. [Epub ahead of print]

Fine tuning of σE activation suppresses multiple assembly-defective mutations in Escherichia coli.

Author information

1
Department of Molecular Biology, Princeton University, Princeton, NJ, 08540.
2
Laboratory of Virology and Infectious Disease, The Rockefeller University, 1230 York Avenue, Box 64, New York, NY, 10065.
3
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, 02138.
4
Novartis Institute for BioMedical Research, Inc., Cambridge, MA, 02139.
5
Emory Antibiotic Resistance Center, Emory University School of Medicine, Atlanta, GA, 30322.
6
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA, 30322.
7
Division of Infectious Disease, Department of Medicine, Emory University School of Medicine, Atlanta, GA, 30322.
8
Department of Molecular Biology, Princeton University, Princeton, NJ, 08540 tsilhavy@princeton.edu.

Abstract

The Gram-negative outer membrane (OM) is a selectively permeable asymmetric bilayer that allows vital nutrients to diffuse into the cell but prevents toxins and hydrophobic molecules from entering. Functionally and structurally diverse β-barrel outer membrane proteins (OMPs) build and maintain the permeability barrier, making the assembly of OMPs crucial for cell viability. In this work, we characterize an assembly-defective mutant of the maltoporin LamB, lamBG439D We show that the folding defect of LamBG439D results in an accumulation of unfolded substrate that is toxic to the cell when the periplasmic protease DegP is removed. Selection for suppressors of this toxicity identified the novel mutant degSA323E allele. The mutant DegSA323E protein contains an amino acid substitution at the PDZ/protease domain interface that results in a partially activated conformation of this protein. This activation increases basal levels of downstream σE stress response signaling. Furthermore, the enhanced σE activity of degSA323E suppresses a number of other assembly-defective conditions without exhibiting the toxicity associated with high levels of σE activity. We propose that the increased basal levels of σE signaling primes the cell to respond to envelope stress before OMP assembly defects threaten cell viability. This finding addresses the importance of envelope stress responses in monitoring the OMP assembly process and underpins the critical balance between envelope defects and stress response activation.Importance Gram-negative bacteria, such as Escherichia coli, inhabit a natural environment that is prone to flux. In order to cope with shifting growth conditions and the changing availability of nutrients, cells must be capable of quickly responding to stress. Stress response pathways allow cells to rapidly shift gene expression profiles to ensure survival in this unpredictable environment. Here, we describe a mutant that partially activates the σE stress response pathway. The elevated basal level of this stress response allows the cell to quickly respond to overwhelming stress to ensure cell survival.

PMID:
30858299
DOI:
10.1128/JB.00745-18

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