Inhibition of Sirtuin Deacylase Activity by Peroxynitrite.

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Sirtuins are NAD+-dependent deacetylases crucial for cellular protection.
• Loss of sirtuin activity is linked to aging and disease.
• Nitric oxide (NO)-derived modifications like S-nitrosation inhibit sirtuins.

Purpose of the Study:

• To compare the effects of peroxynitrite (ONOO−) on human sirtuin deacylase activity.
• To identify post-translational modifications induced by peroxynitrite in sirtuins.

Main Methods:

• Treatment of human sirtuin isoforms (SIRT1-3, 5, 6) with peroxynitrite donor (SIN-1).
• Assay of sirtuin deacylase activity.
• Mass spectrometry for identifying protein modifications (tyrosine nitration, cysteine sulfenylation).

Main Results:

• Peroxynitrite inhibited SIRT1, SIRT2, SIRT3, SIRT5, and SIRT6 deacylase activity.
• Inhibition correlated with increased tyrosine nitration across multiple sirtuin isoforms.
• Novel tyrosine nitration sites were identified within the catalytic cores of SIRT1, SIRT3, SIRT5, and SIRT6.
• Peroxynitrite-mediated cysteine sulfenylation was detected only in SIRT1, with transient sulfenylation and disulfide bond formation in SIRT6.

Conclusions:

• Peroxynitrite, an aging-related oxidant, post-translationally modifies and inhibits key human sirtuin enzymes.
• Tyrosine nitration within the catalytic core is a likely mechanism for sirtuin inhibition.
• These findings suggest a role for peroxynitrite-induced sirtuin inhibition in aging-related disease susceptibility.