Endogenous H2O2 produced by Streptococcus pneumoniae controls FabF activity

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• The Fatty Acid Synthase II (FASII) pathway is essential for bacterial membrane biosynthesis.
• FabF is a key elongation condensing enzyme in the FASII pathway, dictating product specificity.
• Streptococcus pneumoniae generates high levels of hydrogen peroxide (H2O2) via pyruvate oxidase (SpxB).

Purpose of the Study:

• To investigate the role of endogenous H2O2 in regulating FabF activity in Streptococcus pneumoniae.
• To determine if H2O2 directly oxidizes and inhibits the FabF enzyme.

Main Methods:

• Utilizing thiol trapping methods to assess the redox state of FabF cysteines in wild-type and spxB mutant strains.
• Performing in vitro oxidation assays with purified FabF and varying H2O2 concentrations.
• Employing cerulenin to specifically block the FabF active site cysteine.

Main Results:

• Endogenous H2O2 produced by S. pneumoniae specifically oxidizes the catalytic cysteine residue in the FabF active site.
• FabF cysteine oxidation was observed in the wild-type strain but not in the H2O2-deficient spxB mutant.
• Inhibition of FabF by H2O2 or cerulenin led to significant alterations in membrane fatty acid composition.

Conclusions:

• FabF activity in Streptococcus pneumoniae is inhibited by endogenously produced H2O2.
• Oxidative modification of the active site cysteine is the mechanism of H2O2-mediated FabF inhibition.
• This regulation impacts bacterial membrane composition and potentially virulence.