N-acetylaspartylglutamate synthetase II synthesizes N-acetylaspartylglutamylglutamate

J Biol Chem. 2011 May 13;286(19):16693-706. doi: 10.1074/jbc.M111.230136. Epub 2011 Mar 25.


N-Acetylaspartylglutamate (NAAG) is found at high concentrations in the vertebrate nervous system. NAAG is an agonist at group II metabotropic glutamate receptors. In addition to its role as a neuropeptide, a number of functions have been proposed for NAAG, including a role as a non-excitotoxic transport form of glutamate and a molecular water pump. We recently identified a NAAG synthetase (now renamed NAAG synthetase I, NAAGS-I), encoded by the ribosomal modification protein rimK-like family member B (Rimklb) gene, as a member of the ATP-grasp protein family. We show here that a structurally related protein, encoded by the ribosomal modification protein rimK-like family member A (Rimkla) gene, is another NAAG synthetase (NAAGS-II), which in addition, synthesizes the N-acetylated tripeptide N-acetylaspartylglutamylglutamate (NAAG(2)). In contrast, NAAG(2) synthetase activity was undetectable in cells expressing NAAGS-I. Furthermore, we demonstrate by mass spectrometry the presence of NAAG(2) in murine brain tissue and sciatic nerves. The highest concentrations of both, NAAG(2) and NAAG, were found in sciatic nerves, spinal cord, and the brain stem, in accordance with the expression level of NAAGS-II. To our knowledge the presence of NAAG(2) in the vertebrate nervous system has not been described before. The physiological role of NAAG(2), e.g. whether it acts as a neurotransmitter, remains to be determined.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Brain / metabolism
  • CHO Cells
  • Cathepsin A / chemistry
  • Cricetinae
  • Cricetulus
  • Dipeptides / biosynthesis
  • Glutamate Carboxypeptidase II / chemistry
  • Glutamate Carboxypeptidase II / physiology*
  • Humans
  • Mice
  • Molecular Sequence Data
  • Plasmids / metabolism
  • Sciatic Nerve / metabolism
  • Sequence Homology, Amino Acid
  • Spectrometry, Mass, Electrospray Ionization / methods


  • Dipeptides
  • isospaglumic acid
  • Cathepsin A
  • Glutamate Carboxypeptidase II