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Published on: November 25, 2017
Residual mannosidase activity in human mannosidosis: characterization of the mutant enzyme
Abstract:
The prenatal diagnosis of affected fetuses in two families at risk for mannosidosis gave us the opportunity to study the residual alpha-mannosidase activity. We found an altered acidic alpha-mannosidase characterized by lowered affinity toward the substrate, displacement of maximal activity toward pH 4-5, thermal lability, different migration in electrophoresis, and apparent change in molecular weight at alkaline pHs. The immunological properties seem unchanged since the enzyme was precipitated by an antiacidic alpha-mannosidase antiserum. The mutant enzyme instability, provoked by dialysis, and its reactivation after addition of dialysis fluid, suggests an association-dissociation phenomenon. We propose a possible hypothesis that a low molecular weight ligand is necessary to maintain the activity of the mutant enzyme.
Insights
Prenatal diagnosis revealed altered alpha-mannosidase in mannosidosis patients. This mutant enzyme shows instability and altered properties, suggesting a need for a specific ligand to maintain activity.
Area of Science:
- Biochemistry
- Genetics
- Enzymology
Background:
- Mannosidosis is a rare genetic lysosomal storage disorder.
- Deficiency in alpha-mannosidase leads to accumulation of mannose-rich glycoproteins.
Purpose of the Study:
- To characterize the residual alpha-mannosidase activity in fetuses diagnosed with mannosidosis.
- To investigate the biochemical and biophysical properties of the mutant alpha-mannosidase enzyme.
Main Methods:
- Enzyme activity assays at different pH values.
- Electrophoresis and molecular weight determination.
- Immunoprecipitation using specific antiserum.
Main Results:
- The mutant alpha-mannosidase exhibited reduced substrate affinity and thermal lability.
- Maximal enzyme activity was observed at a lower pH (4-5).
- The enzyme showed instability upon dialysis, with reactivation upon addition of dialysis fluid, suggesting an association-dissociation mechanism.
Conclusions:
- The study identified an altered acidic alpha-mannosidase in prenatal mannosidosis cases.
- The mutant enzyme's properties suggest a potential structural defect.
- A hypothesis is proposed that a low molecular weight ligand is essential for maintaining the mutant enzyme's activity.
