Evidence for a second regulatory binding site on PspF that is occupied by the C-terminal domain of PspA

Biophysical and Computational Approaches to Unravel pH-Dependent Conformational Change of PspA Assist PspA-PspF Complex Formation in Yersinia enterocolitica

In enteropathogen, Yersinia enterocolitica, the genes encoding phage shock proteins are organized in an operon (pspA-E), which is activated at the various types of cellular stress (i.e., extracytoplasmic or envelop stress) whereas, PspA negatively regulates PspF, a transcriptional activator of pspA-E and pspG, and is also involved in other cellular machinery maintenance processes. The exact mechanism of association and dissociation of PspA and PspF during the stress response is not entirely clear. In this concern, we address conformational change of PspA in different pH conditions using various in-silico and biophysical methods. At the near-neutral pH, CD and FTIR measurements reveal a ß-like conformational change of PspA; however, AFM measurement indicates the lower oligomeric form at the above-mentioned pH. Additionally, the results of the MD simulation also support the conformational changes which indicate salt-bridge strength takes an intermediate position compared to other pHs. Furthermore, the bio-layer interferometry study confirms the stable complex formation that takes place between PspA and PspF at the near-neutral pH. It, thus, appears that PspA conformational change in adverse pH conditions abandons PspF from having a stable complex with it, and thus, the latter can act as a trans-activator. Taken together, it seems that PspA alone can transduce adverse signals by changing its conformation.

Phage shock protein and gene responses of Escherichia coli exposed to carbon nanotubes

Two-dimensional electrophoretic, western blotting, and quantitative polymerase chain reaction analyses of Escherichia coli cells exposed to pristine single walled carbon nanotubes (SWCNTs), and hydroxyl and carboxylic functionalized SWCNTs (SWCNT-OHs and SWCNT-COOHs) were conducted. SWCNT concentration and length were experimental variables. Exposing E. coli cells to SWCNTs led to changes in protein and gene expressions. Several proteins altered their regulations at a low SWCNT concentration (10 μg/ml) and were shut down at a high SWCNT concentration (100 μg/ml). The expressions of the phage shock protein (psp) operon including pspA, pspB, and pspC genes responded to the membrane stressors, SWCNTs, were also examined. While pspA and pspC expressions were influenced by the length, concentration, and functional groups of SWCNTs, pspB expression was not induced by SWCNTs. The alterations in phage shock protein and gene expressions indicated that SWCNTs caused cell membrane perturbation.

Evidence for an Adaptation of a Phage-Derived Holin/Endolysin System to Toxin Transport in Clostridioides difficile

The pathogenicity locus (PaLoc) of Clostridioides difficile usually comprises five genes (tcdR, tcdB, tcdE, tcdA, tcdC). While the proteins TcdA and TcdB represent the main toxins of this pathogen, TcdR and TcdC are involved in the regulation of their production. TcdE is a holin family protein, members of which are usually involved in the transport of cell wall-degrading enzymes (endolysins) for phage-induced lysis. In the past, TcdE has been shown to contribute to the release of TcdA and TcdB, but it is unclear whether it mediates a specific transport or rather a lysis of cells. TcdE of C. difficile strains analyzed so far can be produced in three isoforms that are initiated from distinct N-terminal ATG codons. When produced in Escherichia coli, we found that the longest TcdE isoform had a moderate effect on cell growth, whereas the shortest isoform strongly induced lysis. The effect of the longest isoform was inhibitory for cell lysis, implying a regulatory function of the N-terminal 24 residues. We analyzed the PaLoc sequence of 44 C. difficile isolates and found that four of these apparently encode only the short TcdE isoforms, and the most closely related holins from C. difficile phages only possess one of these initiation codons, indicating that an N-terminal extension of TcdE evolved in C. difficile. All PaLoc sequences comprised also a conserved gene encoding a short fragment of an endolysin remnant of a phage holin/endolysin pair. We could produce this peptide, which we named TcdL, and demonstrated by bacterial two-hybrid analysis a self-interaction and an interaction with TcdB that might serve to mediate TcdE-dependent transport.