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Mucolipidosis II is caused by mutations in GNPTA encoding the α/β GlcNAc-1-phosphotransferase


Mucolipidosis II (ML II) is a fatal lysosomal storage disorder resulting from defects in the multimeric GlcNAc-1-phosphotransferase responsible for the initial step in the generation of the mannose 6-phosphate (M6P) recognition marker1. M6P residues on oligosaccharides of newly synthesized lysosomal enzymes are essential for efficient receptor-mediated transport to lysosomes2. We used the recombinant GlcNAc-1-phosphotransferase γ subunit as an affinity matrix to purify an unknown protein identified as the product of GNPTA (encoding GNPTA, previously known as MGC4170). The cDNA encodes a protein of 1,256 amino acids with two putative transmembrane domains and a complex preserved modular structure comprising at least six domains. The N-terminal domain of GNPTA, interrupted by a long insertion, shows similarities to bacterial capsule biosynthesis proteins. We identified seven mutations in GNPTA that lead to premature translational termination in six individuals with ML II. Retroviral transduction of fibroblasts from an individual with ML II resulted in the expression and localization of GNPTA in the Golgi apparatus, accompanied by the correction of hypersecretion of lysosomal enzymes. Our results provide evidence that GNPTA encodes a subunit of GlcNAc-1-phosphotransferase defective in individuals with ML II.

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Figure 1: Identification of the novel Golgi-membrane protein eluted from a GNPTG-affinity matrix.
Figure 2: Modular organization of GNPTA and bacterial capsule biosynthesis proteins.
Figure 3: Retroviral expression of GNPTA in ML II fibroblasts improves hypersecretion of lysosomal enzymes.

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This study was supported by Deutsche Forschungsgemeinschaft (GRK464 to S.T. and SFB470/C6 to T.B.). We thank K. von Figura (University of Göttingen) and M. Cantz (University of Heidelberg) for the cultured fibroblasts from ML II patients (Z.B., M.A. and R.D., respectively).

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Correspondence to Thomas Braulke.

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Supplementary information

Supplementary Fig. 1

Nucleotide sequence and deduced amino acid sequence of human MGC4170. (PDF 301 kb)

Supplementary Fig. 2

Domain organization of human MGC4170 and comparison with Drosophila melanogaster CG8027, Dictyostelium discoideum AAO52495, Entamoeba histolytica EAL52006, Mycobacterium tuberculosis CpsY, and Neisseria meningitides XcbA. (PDF 16 kb)

Supplementary Methods (PDF 21 kb)

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Tiede, S., Storch, S., Lübke, T. et al. Mucolipidosis II is caused by mutations in GNPTA encoding the α/β GlcNAc-1-phosphotransferase. Nat Med 11, 1109–1112 (2005).

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