A newly identified flavoprotein disulfide reductase Har protects Streptococcus pneumoniae against hypothiocyanous acid.

J Biol Chem

Department of Pathology and Biomedical Science, Centre for Free Radical Research, University of Otago Christchurch, Christchurch, New Zealand. Electronic address:

Published: September 2022

AI Article Synopsis

  • Hypothiocyanous acid (HOSCN) is an antimicrobial oxidant made in the human respiratory tract and some bacteria, like Streptococcus pneumoniae, can tolerate it, suggesting a potential target for treatments.
  • Researchers discovered a new enzyme, called Har, in S. pneumoniae that helps reduce HOSCN, similar to mechanisms in mammalian cells, although it isn’t essential for the bacteria’s growth under certain conditions.
  • The study shows that while Har is not vital alone, when combined with a disruption of glutathione (GSH) recycling, deleting this enzyme severely affects bacterial growth, indicating its importance in protecting S. pneumoniae from HOSCN.

Article Abstract

Hypothiocyanous acid (HOSCN) is an antimicrobial oxidant produced from hydrogen peroxide and thiocyanate anions by heme peroxidases in secretory fluids such as in the human respiratory tract. Some respiratory tract pathogens display tolerance to this oxidant, which suggests that there might be therapeutic value in targeting HOSCN defense mechanisms. However, surprisingly little is known about how bacteria protect themselves from HOSCN. We hypothesized that tolerant pathogens have a flavoprotein disulfide reductase that uses NAD(P)H to directly reduce HOSCN, similar to thioredoxin reductase in mammalian cells. Here, we report the discovery of a previously uncharacterized flavoprotein disulfide reductase with HOSCN reductase activity, which we term Har (hypothiocyanous acid reductase), in Streptococcus pneumoniae, a bacterium previously found to be tolerant of HOSCN. S. pneumoniae generates large amounts of hydrogen peroxide that can be converted to HOSCN in the respiratory tract. Using deletion mutants, we demonstrate that the HOSCN reductase is dispensable for growth of S. pneumoniae in the presence of lactoperoxidase and thiocyanate. However, bacterial growth in the HOSCN-generating system was completely crippled when deletion of HOSCN reductase activity was combined with disruption of GSH import or recycling. Our findings identify a new bacterial HOSCN reductase and demonstrate a role for this protein in combination with GSH utilization to protect S. pneumoniae from HOSCN.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9483559PMC
http://dx.doi.org/10.1016/j.jbc.2022.102359DOI Listing

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