title: Determinants of the enzymatic activity and the subcellular localization of aspartate N-acetyltransferase.
abstract: Aspartate N-acetyltransferase (NAT8L, N-acetyltransferase 8-like), the enzyme that synthesizes N-acetylaspartate, is membrane-bound and is at least partially associated with the ER (endoplasmic reticulum). The aim of the present study was to determine which regions of the protein are important for its catalytic activity and its subcellular localization. Transfection of truncated forms of NAT8L into HEK (human embryonic kidney)-293T cells indicated that the 68 N-terminal residues (regions 1 and 2) have no importance for the catalytic activity and the subcellular localization of this enzyme, which was exclusively associated with the ER. Mutation of conserved residues that precede (Arg81 and Glu101, in region 3) or follow (Asp168 and Arg220, in region 5) the putative membrane region (region 4) markedly affected the kinetic properties, suggesting that regions 3 and 5 form the catalytic domain and that the membrane region has a loop structure. Evidence is provided for the membrane region comprising α-helices and the catalytic site being cytosolic. Transfection of chimaeric proteins in which GFP (green fluorescent protein) was fused to different regions of NAT8L indicated that the membrane region (region 4) is necessary and sufficient to target NAT8L to the ER. Thus NAT8L is targeted to the ER membrane by a hydrophobic loop that connects two regions of the catalytic domain.
authors.affiliation: Laboratory of Physiological Chemistry, Université Catholique de Louvain and de Duve Institute, B-1200 Brussels, Belgium.
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Tahay
authors.forename: Elsa
authors.initials: E
authors.lastname: Wiame
authors.forename: Donatienne
authors.initials: D
authors.lastname: Tyteca
authors.forename: Pierre J
authors.initials: PJ
authors.lastname: Courtoy
authors.forename: Emile
authors.initials: E
authors.lastname: Van Schaftingen
mesh_terms: D000123:Acetyltransferases / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane; D006224:Cricetinae; D004721:Endoplasmic Reticulum; D057809:HEK293 Cells; D006801:Humans; D008969:Molecular Sequence Data; D017354:Point Mutation; D011487:Protein Conformation; D021381:Protein Transport
chemical_list: D000123:Acetyltransferases; C046791:aspartate N-acetyltransferase