Molecular identification of N-acetylaspartylglutamate synthase and beta-citrylglutamate synthase.
(2010) Journal of Biological Chemistry — Vol. 285, n° 39, p. 29826-29833 (2010)
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- Authors
Opperdoes, Frederik 
Van Schaftingen, Emile
- Abstract
- The purpose of the present work was to determine the identity of the enzymes that synthesize N-acetylaspartylglutamate (NAAG), the most abundant dipeptide present in vertebrate central nervous system (CNS), and beta-citrylglutamate (BCG), a structural analogue of NAAG present in testis and immature brain. Previous evidence suggests that NAAG is not synthesized on ribosomes, but presumably by a ligase. As attempts to detect this ligase in brain extracts failed, we searched the mammalian genomes for putative enzymes that could catalyse this type of reaction. Mammalian genomes were found to encode two putative ligases homologous to Escherichia coli RIMK, which ligates glutamates to the C-terminus of ribosomal protein S6. One of them, named RIMKLA is almost exclusively expressed in the CNS, whereas RIMKLB, which shares 65 % sequence identity with RIMKLA, is expressed in CNS and testis. Both proteins were expressed in bacteria or HEK293T cells and purified. RIMKLA catalyzed the ATP-dependent synthesis of N-acetylaspartylglutamate from N-acetylaspartate and L-glutamate. RIMKLB catalyzed this reaction, but also the synthesis of beta-citrylglutamate. The nature of the reaction products was confirmed by mass spectrometry and NMR. RIMKLA was shown to produce stoichiometric amounts of NAAG and ADP, in agreement with its belonging to the ATP-grasp family of ligases. The molecular identification of these two enzymes will facilitate progress in the understanding of the function of NAAG and BCG.
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Citations
Collard, F., Stroobant, V., Lamosa, P., Kapanda Nankwa, C., Lambert, D., Muccioli, G., Poupaert, J., Opperdoes, F., & Van Schaftingen, E. (2010). Molecular identification of N-acetylaspartylglutamate synthase and beta-citrylglutamate synthase. Journal of Biological Chemistry, 285(39), 29826-29833. https://doi.org/10.1074/jbc.M110.152629 (Original work published 2010)