The YjfJ protein is the effector of a second PspA/VIPP1 system that is widespread in the Gammaproteobacteria

Maintaining the integrity of the cytoplasmic membrane is crucial for bacterial cell survival. Bacteria have evolved conserved mechanisms to sense, maintain, and repair membrane integrity in response to stress. The phage shock protein (Psp) system is one such mechanism, primarily understood in Gammaproteobacterial species like Escherichia coli and Yersinia enterocolitica.

PspA, an effector of this system, works alongside accessory proteins that sense stress and recruit it to damaged membranes. Homologues of PspA, part of the PspA/VIPP1 family, are found in various bacterial phyla. While most research in Gammaproteobacteria has focused on the canonical Psp response, non-canonical PspA/VIPP1-containing systems have also been described, calling for further genomic analysis.

Analyzing the PspA/VIPP1 content across a diverse range of Gammaproteobacterial genomes, we discovered two phylogenetically distinct subtypes of PspA/VIPP1 proteins: PspA- and YjfJ-like. Both subtypes have similar frequencies. The YjfJ-like proteins constitute a novel subtype of PspA/VIPP1, possessing a unique set of accessory proteins.

In some species, such as the ESKAPE pathogen Pseudomonas aeruginosa, YjfJ-like proteins form the sole PspA/VIPP1-containing system. Our study positions the YjfJ-like-containing systems on par with the PspA system regarding their conservation and distribution in the Gammaproteobacteria. This finding suggests that investigating the biological functions of YjfJ-like proteins would be justified, given their unique presence in some significant human pathogens.