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Journal of Bacteriology, September 2000, p. 4882-4888, Vol. 182, No. 17
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Overexpression of Protease-Deficient DegPS210A Rescues the Lethal Phenotype of Escherichia coli OmpF Assembly Mutants in a degP Background

Rajeev Misra,1,2,* Maria CastilloKeller,1,2 and Ming Deng2,3

Department of Microbiology,1 and Molecular and Cell Biology Program,2 Arizona State University, Tempe, Arizona 85287, and Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 021423

Received 17 February 2000/Accepted 9 June 2000

Replacement of OmpF's conserved carboxy-terminal phenylalanine with dissimilar amino acids severely impaired its assembly into stable trimers. In some instances, interactions of mutant proteins with the outer membrane were also affected, as judged by their hypersensitivity phenotype. Synthesis of all mutant OmpF proteins elevated the expression of periplasmic protease DegP, and synthesis of most of them made its presence obligatory for cell viability. These results showed a critical role for DegP in the event of aberrant outer membrane protein assembly. The lethal phenotype of mutant OmpF proteins in a degP null background was eliminated when a protease-deficient DegPS210A protein was overproduced. Our data showed that this rescue from lethality and a subsequent increase in mutant protein levels in the envelope did not lead to the proper assembly of the mutant proteins in the outer membrane. Rather, a detergent-soluble and thermolabile OmpF species resembling monomers accumulated in the mutants, and to a lesser extent in the parental strain, when DegPS210A was overproduced. Interestingly, this also led to the localization of a significant amount of mutant polypeptides to the inner membrane, where DegPS210A also fractionated. These results suggested that the DegPS210A-mediated rescue from toxicity involved preferential sequestration of misfolded OmpF monomers from the normal assembly pathway.

* Corresponding author. Mailing address: Department of Microbiology, Arizona State University, Tempe, AZ 85287-2701. Phone: (480) 965-3320. Fax: (480) 965-0098. E-mail: rajeev.misra{at}asu.edu.

Journal of Bacteriology, September 2000, p. 4882-4888, Vol. 182, No. 17
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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