title: Molecular identification of aspartate N-acetyltransferase and its mutation in hypoacetylaspartia.
abstract: The brain-specific compound NAA (N-acetylaspartate) occurs almost exclusively in neurons, where its concentration reaches approx. 20 mM. Its abundance is determined in patients by MRS (magnetic resonance spectroscopy) to assess neuronal density and health. The molecular identity of the NAT (N-acetyltransferase) that catalyses NAA synthesis has remained unknown, because the enzyme is membrane-bound and difficult to purify. Database searches indicated that among putative NATs (i.e. proteins homologous with known NATs, but with uncharacterized catalytic activity) encoded by the human and mouse genomes two were almost exclusively expressed in brain, NAT8L and NAT14. Transfection studies in HEK-293T [human embryonic kidney-293 cells expressing the large T-antigen of SV40 (simian virus 40)] indicated that NAT8L, but not NAT14, catalysed the synthesis of NAA from L-aspartate and acetyl-CoA. The specificity of NAT8L, its Km for aspartate and its sensitivity to detergents are similar to those described for brain Asp-NAT. Confocal microscopy analysis of CHO (Chinese-hamster ovary) cells and neurons expressing recombinant NAT8L indicates that it is associated with the ER (endoplasmic reticulum), but not with mitochondria. A mutation search in the NAT8L gene of the only patient known to be deficient in NAA disclosed the presence of a homozygous 19 bp deletion, resulting in a change in reading frame and the absence of production of a functional protein. We conclude that NAT8L, a neuron-specific protein, is responsible for NAA synthesis and is mutated in primary NAA deficiency (hypoacetylaspartia). The molecular identification of this enzyme will lead to new perspectives in the clarification of the function of this most abundant amino acid derivative in neurons and for the diagnosis of hypoacetylaspartia in other patients.
authors.affiliation: Laboratory of Physiological Chemistry, Université Catholique de Louvain and de Duve Institute, B-1200 Brussels, Belgium.
authors.forename: Elsa
authors.initials: E
authors.lastname: Wiame
authors.forename: Donatienne
authors.initials: D
authors.lastname: Tyteca
authors.forename: Nathalie
authors.initials: N
authors.lastname: Pierrot
authors.forename: François
authors.initials: F
authors.lastname: Collard
authors.forename: Mustapha
authors.initials: M
authors.lastname: Amyere
authors.forename: Gaëtane
authors.initials: G
authors.lastname: Noel
authors.forename: Jonathan
authors.initials: J
authors.lastname: Desmedt
authors.forename: Marie-Cécile
authors.initials: MC
authors.lastname: Nassogne
authors.forename: Miikka
authors.initials: M
authors.lastname: Vikkula
authors.forename: Jean-Noël
authors.initials: JN
authors.lastname: Octave
authors.forename: Marie-Françoise
authors.initials: MF
authors.lastname: Vincent
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Courtoy
authors.forename: Eugen
authors.initials: E
authors.lastname: Boltshauser
authors.forename: Emile
authors.initials: E
authors.lastname: van Schaftingen
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism; D000123:Acetyltransferases / Q000235:genetics* / Q000378:metabolism*; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000172:deficiency / Q000378:metabolism; D001483:Base Sequence; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D002384:Catalysis; D002460:Cell Line; D002478:Cells, Cultured; D006224:Cricetinae; D003412:Cricetulus; D030541:Databases, Genetic; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D051381:Rats; D013379:Substrate Specificity; D014162:Transfection
chemical_list: D001224:Aspartic Acid; D000105:Acetyl Coenzyme A; C000179:N-acetylaspartate; D000123:Acetyltransferases; C046791:aspartate N-acetyltransferase