Characterization of a transcriptional factor FevR, involved in improving folding in the periplasm of Escherichia coli.

DegP (HtrA: High Temperature Requirement A) is a periplasmic protease with minor chaperone activity that plays a key role in the quality control of protein folding in the envelope of Escherichia coli. Periplasmic and outer membrane proteins that fail to fold in the periplasm can be proteolysed, while others are chaperoned to their native folded state by DegP. In a ΔdegP strain, E. coli is unable to survive the protein folding stress induced at 42º C. Utilizing this phenotype, we developed a plasmid-based selection of suppression of heat-induced lethality in a ΔdegP strain. Plasmid libraries of various prokaryotic genomes were screened for proteins that overcame heat-induced lethality. We identified FevR, a putative transcription factor from Citrobacter amalonaticus having close homologs in environmental E. coli capable of overcoming envelope stress. Through genetic characterization, FevR is shown to induce expression of a periplasmic chaperone-proline isomerase fkpA. Over-expression of FkpA alone is sufficient to suppress heat-induced lethality of a ΔdegP strain. This study demonstrates the use of genetic selections to uncover the hidden potential of E. coli to improve its protein folding capacity. Differential expression of genes by one of the two homolog transcriptional factor, FevRCit or FevREco105, compared to empty vector, in different conditions: background strain E. coli K-12 DHB4 wild type or ΔdegP, grown at 30°C, with or without a heat shock at 42°C during log phase, or grown at 42°C