sRNA Regulation within the Cpx Stress Response Pathway

Abstract

The Cpx pathway of Escherichia coli contains a two-component stress response system that combats many extra-cytoplasmic toxicities, such as misfolded P-pilus (Pap) proteins. Pap proteins are essential for adhesion in uropathogenic E. coli and are prone to misfolding. The sensing domain histidine kinase CpxA is attached at the inner membrane, phosphorylating the response regulator domain CpxR. CpxR then affects many gene targets within the regulon. CpxP, one of the most regulated protein products of the Cpx regulon, appears to have several jobs within the stress-combative cascade. The periplasmic protein has a signal sequence that directs secretion from the cytoplasm before being cleaved; the mature CpxP acts negatively upon CpxA stimulation, reducing its own transcription, in addition to binding to the misfolded proteins to help attract proteases to degrade offending Pap subunits. In addition, a 3‟ untranslated region (UTR) has been found to produce an sRNA for CpxP. We demonstrate that this cpxP 3‟ UTR, CPxQ, decreases CpxP protein levels; the native CpxP signal sequence is necessary for this post-transcriptional regulation to occur. Specifically, the mechanism by which CpxQ affects CpxP production is still unclear; broadly, the effects of the post-transcriptional regulation are uncharacterized within the Cpx pathway. Additionally, we find that deletion of the CpxQ reverses a constitutively active mutation of CpxA and hinders stress alleviation in the periplasm. Therefore, we suggest the model that CpxP is the harbinger protein of the negative feedback mechanism for the Cpx stress response pathway, while CpxQ acts like a riboswitch.