Purification and characterization of human lymphoblast N-acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase

Association study of stuttering candidate genes GNPTAB, GNPTG and NAGPA with dyslexia in Chinese population

Background

Dyslexia is a polygenic speech and language disorder characterized by an unexpected difficulty in reading in children and adults despite normal intelligence and schooling. Increasing evidence reveals that different speech and language disorders could share common genetic factors. As previous study reported association of GNPTAB, GNPTG and NAGPA with stuttering, we investigated these genes with dyslexia through association analysis.

Results

The study was carried out in an unrelated Chinese cohort with 502 dyslexic individuals and 522 healthy controls. In all, 21 Tag SNPs covering GNPTAB, GNPTG and NAGPA were subjected to genotyping. Association analysis was performed on all SNPs. Significant association of rs17031962 in GNPTAB and rs882294 in NAGPA with developmental dyslexia was identified after FDR correction for multiple comparisons.

Conclusion

Our results revealed that the stuttering risk genes GNPTAB and NAGPA might also associate with developmental dyslexia in the Chinese population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0172-5) contains supplementary material, which is available to authorized users.

Abnormal lysosomal sorting with an enhanced secretion of cathepsin D precursor molecules bearing monoester phosphate groups

It has been reported that besides defects in the phosphorylation such as in the I-cell disease, a failure in the uncovering of mannose 6-phosphate residues may result in an increase of lysosomal enzyme activities in serum [Alexander et al., Hum. Genet. 73, 53-59 (1986)]. We examined fibroblasts that were derived from the original biopsy, observed an enhanced secretion of lysosomal enzymes including cathepsin D, but found that both the phosphorylation and uncovering of mannose 6-phosphate residues were normal. The enhanced secretion of cathepsin D was characterized by an increase in the secretion of phosphorylated molecules that were sensitive to a treatment with alkaline phosphatase. The enhanced secretion of the phosphatase-sensitive form of procathepsin D was further increased in the presence of antibodies directed to cation-independent mannose 6-phosphate receptors. In contrast, antibodies specific to cation-dependent mannose 6-phosphate receptors selectively inhibited the secretion of the phosphatase-sensitive procathepsin D molecules. A chromatographic analysis of oligosaccharides from the secreted procathepsin D confirmed that the cells secrete proenzyme molecules rich in oligosaccharides with two uncovered phosphate residues. It is suggested that the enhanced secretion of procathepsin D in the variant fibroblasts results from an abnormal sorting rather than processing of phosphorylated lysosomal enzymes.

Purification and multimeric structure of bovine N-acetylglucosamine-1-phosphodiester alpha-N-acetylglucosaminidase

N-Acetylglucosamine-1-phosphodiester alpha-N-Acetylglucosaminidase (EC 3.1.4.45; phosphodiester alpha-GlcNAcase) catalyzes the second step in the synthesis of the mannose 6-phosphate determinant required for efficient intracellular targeting of newly synthesized lysosomal hydrolases to the lysosome. A partially purified preparation of phosphodiester alpha-GlcNAcase from bovine pancreas was used to generate a panel of murine monoclonal antibodies. The anti-phosphodiester alpha-GlcNAcase monoclonal antibody UC1 was coupled to a solid support and used to immunopurify the bovine liver enzyme 670,000-fold in two steps to apparent homogeneity with an overall yield of 14%. The purified phosphodiester alpha-GlcNAcase has a specific activity of 498 micromol of [3H]GlcNAc-alpha-phosphomannose-alpha-methyl cleaved per h per mg of protein using 0.5 mM [3H]GlcNAc-alpha-phosphomannose-alpha-methyl as substrate. The subunit structure of the enzyme was determined using a combination of analytical gel filtration chromatography, SDS-polyacrylamide gel electrophoresis, and amino-terminal sequencing. The data indicate that bovine phosphodiester alpha-GlcNAcase is a 272,000-Da complex of four identical 68,000-Da glycoprotein subunits arranged as two disulfide-linked homodimers. A soluble form of the enzyme, isolated from fetal bovine serum, showed the same subunit structure. Both forms of the enzyme reacted with a rabbit antibody raised to the amino-terminal peptide of the liver enzyme, suggesting that phosphodiester alpha-GlcNAcase is a type I membrane-spanning glycoprotein with its amino terminus in the lumen of the Golgi apparatus.

The detection of enzyme activity following sodium dodecyl sulfate-polyacrylamide gel electrophoresis

More than a hundred different enzymes impinging on aspects of cell function ranging from carbohydrate and lipid metabolism to signal transduction and gene expression to biomolecule degradation have been detected by the assay of their enzymatic activities following SDS-PAGE. The strategies by which this has been accomplished are as varied as the enzymes themselves and offer testimony to the creativeness and ingenuity of life scientists. Assay of enzyme activity following SDS-PAGE is well adapted to identifying the source of catalytic activity in a heterogeneous protein mixture or a heterooligomeric protein (20), or determining if multiple catalytic activities reside in a single polypeptide (60). The alliance of versatile enzyme assay techniques with the molecular resolution of SDS-PAGE offers a powerful means for meeting the increasing demand for the high-throughput screening arising from protein engineering, combinatorial chemistry, and functional genomics.