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

• Published in: The Journal of biological chemistry Vol. 298; no. 9; p. 102359
• Main Authors: Shearer, Heather L., Pace, Paul E., Paton, James C., Hampton, Mark B., Dickerhof, Nina
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.09.2022; American Society for Biochemistry and Molecular Biology
• Subjects: flavoprotein disulfide reductase; hypothiocyanous acid; lactoperoxidase; myeloperoxidase; pneumonia; pyridine nucleotide-disulfide reductase; SPD_1415; thioredoxin reductase; BHI; THY; hypothiocyanous acid; SOE; TNB; myeloperoxidase; LPO; GR; flavoprotein disulfide reductase; H2O2; HOSCN; MPO; thioredoxin reductase; SPD_1415; MWCO; pneumonia; IAM; FDR; CAT; Har; pyridine nucleotide-disulfide reductase; lactoperoxidase; SCN; TrxR
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/j.jbc.2022.102359

Hypothiocyanous acid (HOSCN) is an antimicrobial oxidant produced by heme peroxidases from hydrogen peroxide and thiocyanate anions in secretory fluids such as in the human respiratory tract. While some respiratory tract pathogens display tolerance to HOSCN, there might be therapeutic value in targeting bacterial antioxidant systems that protect against HOSCN; however, surprisingly, little is known about the bacterial defense mechanisms involved. 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 knockouts, we demonstrate that the HOSCN reductase is dispensable for growth of S. pneumoniae in the presence of lactoperoxidase and thiocyanate. However, we also show that 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.