Kynurenine aminotransferase activity of Aro8/Aro9 engage tryptophan degradation by producing kynurenic acid in Saccharomyces cerevisiae

Abstract

Kynurenic acid (KA) is a tryptophan (Trp) metabolite that is synthesised in a branch of kynurenine (KYN) pathway. KYN aminotransferase (KAT) catalyses deamination of KYN, yielding KA. Although KA synthesis is evolutionarily conserved from bacteria to humans, the cellular benefits of synthesising KA are unclear. In this study, we constructed a KAT-null yeast mutant defective in KA synthesis to clarify the cellular function of KA. Amino acid sequence analysis and LC/MS quantification of KA revealed that Aro8 and Aro9 are the major KATs. KA was significantly decreased in the aro8Δ aro9Δ double mutant. We found that aro8Δ aro9Δ cells did not exhibit obvious defects in growth or oxidative stress response when proper amounts of amino acids are supplied in the media. We further found that aro8Δ aro9Δ cells were sensitive to excess Trp. The Trp sensitivity was not rescued by addition of KA, suggesting that Trp sensitivity is not due to the loss of KA. In conclusion, we propose that KAT activity is required for detoxification of Trp by converting it to the less toxic KA.

Biochemical Characterization of Aspergillus fumigatus AroH, a Putative Aromatic Amino Acid Aminotransferase

“…As compared with similar enzymes, AroH displays an analogous preference for L-tyrosine, L-phenylalanine and α-aminoadipate as amino donors (Karsten et al, 2011 ). We also demonstrated that it is able to metabolize L-kynurenine, as already suggested for Aro8 based on studies on knock-out yeast mutants (Ohashi et al, 2017 ) reporting that the enzyme is responsible for tryptophan catabolism to kynurenic acid. However, it should be pointed out that the K m of L-kynurenine of AroH is 5 to 20-fold higher than that for aromatic substrates.…”

“…Yeast Aro8 is a broad specificity dimeric aminotransferase belonging to the Fold Type I family of PLP-enzymes (Bulfer et al, 2013 ), able to metabolize both aromatic amino acids and α-aminoadipate (Iraqui et al, 1998 ). It has been recently claimed as one of the enzymes involved in L-tryptophan degradation (Ohashi et al, 2017 ). A detailed study on the main genes playing a role in A. fumigatus virulence, does not include Aro proteins (Abad et al, 2010 ).…”

An efficient method for production of kynurenic acid by Yarrowia lipolytica

“…The presence of KYNA in yeast raises the question about its role in microorganisms. It was suggested that KYNA pathway can be essential for the detoxification of tryptophan excess and remain the way for the transformation of this amino acid to the less toxic KYNA (Ohashi, Chaleckis, Takaine, Wheelock, & Yoshida, 2017). In addition to yeasts, the kynurenine pathway was documented in some prokaryotes such as Streptomyces antibioticus and Xanthomonas pruni (Kurnasov et al, 2003).…”

“…Kynurenine pathway is crucial in prokaryotic and eukaryotic cells for tryptophan catabolism and synthesis of the important cofactor NAD + (Ohashi et al, 2017). KYNA is formed along the kynurenine pathway via deamination of kynurenine; the enzymatic step is catalysed by kynurenine aminotransferases (KATs).…”

Proteomic Analysis of Saccharomyces cerevisiae Response to Oxidative Stress Mediated by Cocoa Polyphenols Extract

“…Aro8 is an aromatic aminotransferase involved in aromatic amino acids metabolism (tryptophan, tyrosine, and phenylalanine). Aro8 takes part in the branch of the kynurenine pathway by synthesizing kynurenic acid indirectly from tryptophan (Trp) [29]. Free tryptophan can be metabolized in vivo and play key roles as an antioxidant [30].…”