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Expression and specificity of human GM2 activator protein
Y Y Wu1, J M Lockyer, E Sugiyama
1Department of Biochemistry, Tulane University School of Medicine, New Orleans, Louisiana 70112.
The Journal of Biological Chemistry
|June 10, 1994
Summary
Recombinant GM2 activator protein, produced in E. coli, shows broad substrate specificity, stimulating reactions beyond GM2 hydrolysis. Its mechanism differs from saposin B, suggesting a role beyond simple lipid solubilization.
Area of Science:
- Biochemistry
- Molecular Biology
- Enzymology
Background:
- GM2 activator is crucial for the lysosomal degradation of the glycosphingolipid GM2.
- Previous studies suggested a highly specific role for GM2 activator in GM2 hydrolysis by beta-N-acetylhexosaminidase A (Hex A).
Purpose of the Study:
- To produce and characterize recombinant GM2 activator.
- To critically re-evaluate the substrate specificity and mechanism of action of GM2 activator.
Main Methods:
- Expression of GM2 activator cDNA in Escherichia coli/pT7-7 system.
- Purification and activity assessment of recombinant GM2 activator.
- Enzymatic assays to determine substrate specificity and activator interactions.
Main Results:
- High-yield, high-purity recombinant GM2 activator was produced, exhibiting activity comparable to native human GM2 activator.
- GM2 activator demonstrated broader substrate specificity than previously reported, stimulating hydrolysis of other glycosphingolipids and acting with different enzymes.
- The activator showed no differentiation between certain lipid substrates or enzymes, and its effectiveness may stem from recognizing the GM2 epitope's trisaccharide structure.
Conclusions:
- The specificity of GM2 activator is not as strict as previously assumed.
- The mechanism of GM2 activator action is distinct from saposin B and involves more than just lipid solubilization.
- GM2 activator's effectiveness in GM2 hydrolysis likely involves specific recognition of the GM2 epitope and modification of key interactions within it.