The Chaperone Activities of DsbG and Spy Restore Peptidoglycan Biosynthesis in the elyC Mutant by Preventing Envelope Protein Aggregation.

Peptidoglycan (PG) is the main structural component of bacterial envelopes. It protects bacterial cells against variations in osmotic pressure and cell lysis. The newly discovered Escherichia coli factor ElyC has been shown to be important for peptidoglycan biosynthesis at low temperatures. PG production in Δ elyC mutant cells is totally blocked after a few hours of growth at 21°C, triggering cell lysis. In this study, we took a candidate approach to identify genetic suppressors of the Δ elyC mutant cell lysis phenotype. We identified the periplasmic proteins DsbG and Spy as multicopy suppressors and showed that their overproduction restores PG biosynthesis in the Δ elyC mutant. Interestingly, we found that DsbG acts by a novel mechanism, which is independent of its known reductase activity and substrates. DsbG, like Spy, acts as a chaperone to reduce the amounts of protein aggregates in the envelopes of Δ elyC cells. In fact, we found that the amount of protein aggregates was greater in the Δ elyC mutant than in the wild type. Taken together, our results show a protein-folding defect in the envelope compartments of Δ elyC cells that blocks PG production, and they reveal a new physiological activity of DsbG. IMPORTANCE Peptidoglycan biosynthesis is a dynamic and well-controlled pathway. The molecular assembly of PG and the regulatory pathways ensuring its maintenance are still not well understood. Here we studied the newly discovered Escherichia coli factor ElyC, which is important for PG biosynthesis at low temperatures. We revealed an important protein-folding defect in the Δ elyC mutant and showed that overproduction of the periplasmic chaperone DsbG or Spy was sufficient to correct the protein-folding defect and restore PG biosynthesis. These results show that the PG defect in the absence of ElyC is caused, at least in part, by a protein-folding problem in the cell envelope. Furthermore, we showed, for the first time, that the periplasmic protein DsbG has chaperone activity in vivo .