Tyrosyl-tRNA synthetase: A potential kyotorphin synthetase in mammals

• Published in: Peptides (New York, N.Y. : 1980) N.Y. : 1980), 2018-03, Vol.101, p.60-68
• Main Authors: Tsukahara, Tamotsu, Yamagishi, Shuhei, Neyama, Hiroyuki, Ueda, Hiroshi
• Format: Article
• Language: English
• Subjects: Animals; Arginine; Brain; Dipeptide; Endorphins - biosynthesis; Endorphins - genetics; Gene Expression Regulation, Enzymologic - physiology; Gene Knockdown Techniques; Humans; Kyotorphin; Male; Medulla Oblongata - cytology; Medulla Oblongata - enzymology; Mesencephalon - cytology; Mesencephalon - enzymology; Mice; PC12 Cells; Peptide Synthases - biosynthesis; Peptide Synthases - genetics; Rats; Tyrosine; Tyrosine-tRNA Ligase - biosynthesis; Tyrosine-tRNA Ligase - genetics; Tyrosyl-tRNA synthetase
• ISSN: 0196-9781; 1873-5169
• DOI: 10.1016/j.peptides.2017.12.026

•TyrRS mRNA expression was highest in brain regions.•TyrRS accepted a wide variety of amino acids as substrates.•PC12 cells of TyrRS involved in the formation of kyotorphin.•KTP levels in brains are increased after Arg administration. Kyotorphin (KTP; L-tyrosyl-l-arginine), an opioid-like analgesic discovered in the bovine brain, is potentially a neuromodulator because of its localization in synaptosomes, the existence of a specific KTP receptor, and the presence of its biosynthetic enzyme in the brain. KTP is formed in the brain from its constituent amino acids, L-tyrosine and L-arginine, by an enzyme termed KTP synthetase. However, the latter has never been identified. We aimed to test the hypothesis that tyrosyl-tRNA synthetase (TyrRS) is also KTP synthetase. We found that recombinant hTyrRS synthesizes KTP from tyrosine, arginine, and ATP, with Km = 1400 μM and 200 μM for arginine and tyrosine, respectively. TyrRS knockdown of PC12 cells with a small interfering RNA (siRNA) in the presence of 1.6 mM tyrosine, arginine, proline, or tryptophan significantly reduced the level of KTP, but not those of tyrosine-tyrosine, tyrosine-proline, or tyrosine-tryptophan. siRNA treatment did not affect cell survival or proliferation. In mice, TyrRS levels were found to be greater in the midbrain and medulla oblongata than in other brain regions. When arginine was administered 2 h prior to brain dissection, the KTP levels in these regions plus olfactory bulb significantly increased, although basal brain KTP levels remained relatively even. Our conclusion is further supported by a positive correlation across brain regions between TyrRS expression and arginine-accelerated KTP production.