Unveiling the Role of Heat Shock Proteins

A protective function against protein clumping is provided by a heat shock protein within cells.

However, its efficacy diminishes with prolonged treatment. In wound therapy against antibiotic-resistant pathogens, plasmas find application. Despite this, bacteria can mount a defense by utilizing a heat shock protein for protection.

Professor Julia Bandow and Dr Tim Dirks, leading a research team at the Chair for Applied Microbiology at Ruhr University Bochum, Germany, revealed that bacteria exhibiting increased production of the heat shock protein Hsp33 display greater resistance to plasma treatment.

Additionally, the researchers identified the specific components of the plasma responsible for activating the heat shock protein.

The research group published their findings in the Journal of the Royal Society Interface on October 25^th, 2023.

All bacteria inactivated after three minutes

Exposure to plasma induces the unfolding of proteins, causing a loss of their natural functions and the potential formation of clumps. The aggregation of proteins is harmful to cells, leading to their deactivation. Hsp33, a bacterial heat shock protein with a molecular weight of 33 kDa (kilo Dalton), counteracts clumping by binding to the unfolded proteins.

To investigate whether an excess of Hsp33 provides cellular protection against plasma, the researchers subjected strains that overexpressed the protein to treatment using the Cinogy plasma source, commonly employed in dermatology.

These strains exhibited significantly enhanced survival compared to wild-type bacteria following a brief treatment lasting approximately one minute.

After a treatment of three minutes, the cells that produce Hsp33 in excess were also inactivated.”

Dr Tim Dirks, Chair, Applied Microbiology, Ruhr University Bochum

Species that activate the heat shock protein

The researchers demonstrated the activation of Hsp33 by exposing the purified heat shock protein to the plasma source.

This activation is associated with the oxidation and unfolding of the protein and is actually reversible. However, we also showed that Hsp33 was completely degraded by longer plasma treatment times of one hour.”

Dr Tim Dirks, Chair, Applied Microbiology, Ruhr University Bochum

Furthermore, plasma negatively impacted the protein's capacity to bind a zinc atom. This zinc atom plays a crucial role in reinforcing the natural three-dimensional structure of the protein when it is in its inactive state.

Prior to this study, there was no knowledge regarding the plasma-produced species that could activate Hsp33. To address this, the researchers generated various stressors known to be produced by plasma and systematically treated Hsp33 with each one.

This showed that Hsp33 is activated by superoxide, singular oxygen, and atomic oxygen, but doesn’t react to hydroxyl radicals and peroxynitrite.”

Dr Tim Dirks, Chair, Applied Microbiology, Ruhr University Bochum

This provides insight into how these species interact with bacterial cells. For instance, superoxide is among the initial species produced during oxidative stress, as observed in the body's immune response, particularly in macrophages. A prompt reaction of Hsp33 to such early-generated species would be advantageous for the bacterium, enabling swift protection against oxidative stress.

“Superoxide appears to act as a signaling molecule for bacteria, which signals further oxidative stress,” concluded the research team.