The molecular chaperone Hsp33 is activated by atmospheric-pressure plasma protecting proteins from aggregation

Abstract

Non-equilibrium atmospheric-pressure plasmas are an alternative means to sterilize and disinfect. Plasma-mediated protein aggregation has been identified as one of the mechanisms responsible for the antibacterial features of plasma. Heat shock protein 33 (Hsp33) is a chaperone with holdase function that is activated when oxidative stress and unfolding conditions coincide. In its active form, it binds unfolded proteins and prevents their aggregation. Here we analyse the influence of plasma on the structure and function of Hsp33 of Escherichia coli using a dielectric barrier discharge plasma. While most other proteins studied so far were rapidly inactivated by atmospheric-pressure plasma, exposure to plasma activated Hsp33. Both, oxidation of cysteine residues and partial unfolding of Hsp33 were observed after plasma treatment. Plasma-mediated activation of Hsp33 was reversible by reducing agents, indicating that cysteine residues critical for regulation of Hsp33 activity were not irreversibly oxidized. However, the reduction yielded a protein that did not regain its original fold. Nevertheless, a second round of plasma treatment resulted again in a fully active protein that was unfolded to an even higher degree. These conformational states were not previously observed after chemical activation with HOCl. Thus, although we could detect the formation of HOCl in the liquid phase during plasma treatment, we conclude that other species must be involved in plasma activation of Hsp33. E. coli cells over-expressing the Hsp33-encoding gene hslO from a plasmid showed increased survival rates when treated with plasma while an hslO deletion mutant was hypersensitive emphasizing the importance of protein aggregation as an inactivation mechanism of plasma.

Surviving Reactive Chlorine Stress: Responses of Gram-Negative Bacteria to Hypochlorous Acid

“…These modifications lead to the formation of the dimeric activated Hsp33. The unfolded region binds to unfolded proteins, avoiding their non-specific aggregation [ 43 , 92 ]. When oxidative stress is under control, Hsp33 releases the unfolded protein and returns to the reduced state.…”

Plasma‐Driven in Situ Production of Hydrogen Peroxide for Biocatalysis

“…It is worth mentioning here that the extent of deleterious effects of plasmas are dependent on the enzyme. Some enzymes even exhibited increased activity after plasma treatment …”

Inactivation of airborne bacteria by plasma treatment and ionic wind for indoor air cleaning

“…Thus, in a study with plasma‐sensitive mutants, 87 genes were identified that possessed a protective function against a plasma that was applied for the treatment of bacteria‐containing solutions. [ 45 ] These genes encoded, for example, transcriptional factors to prevent DNA alkylation and initiate DNA repair mechanisms. Other genes encoded structural proteins involved in motility or biofilm formation as well as iron‐containing proteins involved in pathways such as respiratory electron transport chain.…”

“…Other genes encoded structural proteins involved in motility or biofilm formation as well as iron‐containing proteins involved in pathways such as respiratory electron transport chain. [ 45 ] In general, DNA strand breaks or DNA lesions possibly caused by modified nucleobases can be formed by (V)UV radiation or reactive species such as ozone or hydroxyl radicals. [ 46,47 ] Such effects were also described for plasma treatments using plasmid‐containing solutions [ 48 ] or plasmid solutions dried on glass carriers.…”