The Protein quality control in bacterial periplasm as a drug target for protein conformational diseases

Aberrant folding has been linked to many human pathologies, including neurodegenerative diseases and cell death in prokaryotes. Both prokaryotic and eukaryotic cells evolving an intricate protein quality control (PQC) system maintaining protein homeostasis. E.coli cope with fluctuating environments during their life cycle, facing temperature shifts, oxidative stress, and acidic stress, precisely the same conditions that lead to protein unfolding and aggregation. The first line of defense in these pathogens is the periplasm region that contains a fine-tuned PQC system.
Here, we aim to understand the amazing periplasmic folding machine, characterizing the interplay between participants in the periplasm PQC system. We used several aggregation-prone proteins based on polyQ expansion. Preliminary results showed that protein aggregation mainly occurs in the cytosol, not in the periplasm, indicating unique chaperone activity of periplasmic proteostatic network.
We examined aggregation propensity of PolyQ variants in different strains lacking diverse periplasmic chaperones. Depletion of specific members of the PQC system had no impact on protein solubility in the cytosol, rather reduced aggregate abundance in periplasm. Surprisingly, depletion of the crucial periplasmic chaperone, surA, significantly increased the solubility of the polyQ- aggregates in the periplasm, indicating alternative or independent mechanisms activated absent surA.
Quantitative proteomics of ∆SurA and wild type strains uncovered significance up-regulation of other periplasmic chaperones such as spy and degP. Down-regulated proteins were mainly related to cytosolic chaperones, general stress response and redox homeostasis. This project has the potential to discover antibacterial drug targets to gram negative pathogens and develop novel inhibitors of PolyQ-mediated aggregation.