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Periplasmic chaperone FkpA is essential for imported colicin M toxicity
Article first published online: 28 JUN 2008
© 2008 The Authors. Journal compilation © 2008 Blackwell Publishing Ltd
Volume 69, Issue 4, pages 926–937, August 2008
How to Cite
Hullmann, J., Patzer, S. I., Römer, C., Hantke, K. and Braun, V. (2008), Periplasmic chaperone FkpA is essential for imported colicin M toxicity. Molecular Microbiology, 69: 926–937. doi: 10.1111/j.1365-2958.2008.06327.x
- Issue published online: 23 JUL 2008
- Article first published online: 28 JUN 2008
- Accepted 1 June, 2008.
Chaperones facilitate correct folding of newly synthesized proteins. We show here that the periplasmic FkpA chaperone is required for killing Escherichia coli by colicin M entering cells from the outside. Highly active colicin M preparations were inactive against fkpA mutant cells; 104-fold dilutions killed fkpA+ cells. Three previously isolated spontaneous mutants tolerant to colicin M carried a stop codon or an IS1 insertion in the peptidyl-prolyl-cis-trans-isomerase (PPIase) domain (C-domain) of FkpA, which resulted in deletion of the domain. A randomly generated mutant carried a G148D mutation in the C-domain. A temperature-sensitive mutant tolerant to colicin M carried a Y25N mutation in the FkpA N-domain. Mutants transformed with wild-type fkpA were colicin M-sensitive. Isolated FkpA-His reduced colicin M-His cleavage by proteinase K and renatured denatured colicin M-His in vitro; renaturation was prevented by the PPIase inhibitor FK506. In both assays, periplasmic SurA-His had no effect. No other tested periplasmic chaperone could activate colicin M. Among the tested colicins, only colicin M required FkpA for activity. Colicin M bound to cells via FhuA was inactivated by trypsin; unbound colicin M retained activity. We propose that colicin M unfolds during import across the outer membrane, FkpA specifically assists in folding colicin M into an active toxin in the periplasm and PPIase is essential for colicin M activity. Colicin M is a suitable tool for the isolation of FkpA mutants used to elucidate the functions of the FkpA N- and C-domains.