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J Biol Chem. 2011 Nov 18;286(46):39786-93. doi: 10.1074/jbc.M111.295899. Epub 2011 Sep 28.

Analysis of mannose 6-phosphate uncovering enzyme mutations associated with persistent stuttering.

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  • 1Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri 63110, USA.

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.

PMID:
21956109
[PubMed - indexed for MEDLINE]
PMCID:
PMC3220557
Free PMC Article

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