title: Analysis of mannose 6-phosphate uncovering enzyme mutations associated with persistent stuttering.
abstract: GlcNAc-1-phosphodiester-N-acetylglucosaminidase ("uncovering enzyme" (UCE); EC 3.1.4.45) is a Golgi enzyme that mediates the second step in the synthesis of the mannose 6-phosphate lysosomal targeting signal on acid hydrolases. Recently, three mutations (two missense and one deletion/frameshift) in the NAGPA gene that encodes UCE have been identified in individuals with persistent stuttering. We now demonstrate that each mutation leads to lower cellular UCE activity. The p.R328C mutation impairs folding in the endoplasmic reticulum, resulting in degradation of a significant portion by the proteasomal system. The p.H84Q mutation also impairs folding and, in addition, decreases the specific activity of the enzyme that folds sufficiently to traffic to the Golgi. The p.F513SfsX113 frameshift mutation adds 113 amino acids to the C terminus of the cytoplasmic tail of the protein, including a VWLL sequence that causes rapid degradation via the proteasomal system. These biochemical findings extend the genetic data implicating mutations in the NAGPA gene in the persistent stuttering phenotype.
authors.affiliation: Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Wang-Sik
authors.initials: WS
authors.lastname: Lee
authors.forename: Changsoo
authors.initials: C
authors.lastname: Kang
authors.forename: Dennis
authors.initials: D
authors.lastname: Drayna
authors.forename: Stuart
authors.initials: S
authors.lastname: Kornfeld
mesh_terms: D019943:Amino Acid Substitution; D005260:Female; D016368:Frameshift Mutation; D006056:Golgi Apparatus / Q000201:enzymology / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D010727:Phosphoric Diester Hydrolases / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000235:genetics; D059748:Proteolysis; D013342:Stuttering / Q000201:enzymology / Q000235:genetics
chemical_list: D010727:Phosphoric Diester Hydrolases; C026645:N-acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase; D046988:Proteasome Endopeptidase Complex