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Myeloperoxidase is synthesized as larger phosphorylated precursor
The EMBO Journal
|November 1, 1984
Summary
Myeloperoxidase (MPO) is synthesized as a large precursor in HL-60 cells and processed into mature fragments. Phosphorylated oligosaccharides on MPO may guide its transport, similar to lysosomal enzymes.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- Myeloperoxidase (MPO) is a key enzyme in neutrophil function.
- Understanding MPO synthesis and processing is crucial for cellular defense mechanisms.
Purpose of the Study:
- To investigate the synthesis and post-translational modifications of myeloperoxidase (MPO).
- To elucidate the processing pathway and potential targeting signals of MPO in human cells.
Main Methods:
- Metabolic labeling of HL-60 cells and in vitro translation using HL-60 mRNA.
- Immunoprecipitation, gel electrophoresis, and fluorography to analyze MPO products.
- Treatment with endo-beta-N-acetylglucosaminidase H and analysis of [32P]phosphate incorporation.
Main Results:
- MPO is synthesized as an 85-K glycosylated precursor, processed to mature 60-K and 13-K fragments.
- In vitro synthesis yielded a 76-K polypeptide or an 87-K glycosylated form.
- [32P]phosphate incorporation into endo-beta-N-acetylglucosaminidase H-sensitive oligosaccharides suggests phosphorylation.
Conclusions:
- MPO undergoes extensive post-translational modification, including glycosylation and proteolytic cleavage.
- Phosphorylated mannose 6-phosphate residues on MPO oligosaccharides likely mediate its sorting and transport.
- MPO processing shares similarities with lysosomal enzyme pathways.