Nit1 is a metabolite repair enzyme that hydrolyzes deaminated glutathione

• Published in: Proceedings of the National Academy of Sciences - PNAS 2017-04, Vol.114 (16), p.E3233-E3242
• Main Authors: Peracchi, Alessio, Veiga-da-Cunha, Maria, Kuhara, Tomiko, Ellens, Kenneth W., Paczia, Nicole, Stroobant, Vincent, Seliga, Agnieszka K., Marlaire, Simon, Jaisson, Stephane, Bommer, Guido T., Sun, Jin, Huebner, Kay, Linster, Carole L., Cooper, Arthur J. L., Van Schaftingen, Emile
• Format: Article
• Language: English
• Subjects: Amidase; Antioxidants; Bacteria; Biological Sciences; E coli; Enzymes; Eukaryotes; Genes; Glutathione; Mammalian cells; Metabolism; Metabolites; Mice; Mitochondria; Mutants; Nitrilase; PNAS Plus; Tumor suppressor genes; Urine; Yeast
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1613736114

The mammalian gene Nit1 (nitrilase-like protein 1) encodes a protein that is highly conserved in eukaryotes and is thought to act as a tumor suppressor. Despite being ∼35% sequence identical to ω-amidase (Nit2), the Nit1 protein does not hydrolyze efficiently α-ketoglutaramate (a known physiological substrate of Nit2), and its actual enzymatic function has so far remained a puzzle. In the present study, we demonstrate that both the mammalian Nit1 and its yeast ortholog are amidases highly active toward deaminated glutathione (dGSH; i.e., a form of glutathione in which the free amino group has been replaced by a carbonyl group). We further show that Nit1-KO mutants of both human and yeast cells accumulate dGSH and the same compound is excreted in large amounts in the urine of Nit1-KO mice. Finally, we show that several mammalian aminotransferases (transaminases), both cytosolic and mitochondrial, can form dGSH via a common (if slow) side-reaction and provide indirect evidence that transaminases are mainly responsible for dGSH formation in cultured mammalian cells. Altogether, these findings delineate a typical instance of metabolite repair, whereby the promiscuous activity of some abundant enzymes of primary metabolism leads to the formation of a useless and potentially harmful compound, which needs a suitable “repair enzyme” to be destroyed or reconverted into a useful metabolite. The need for a dGSH repair reaction does not appear to be limited to eukaryotes: We demonstrate that Nit1 homologs acting as excellent dGSH amidases also occur in Escherichia coli and other glutathione-producing bacteria.