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The MUC1 SEA module is a self-cleaving domain.
Fiana Levitin1, Omer Stern, Mordechai Weiss
1Department of Cell Research and Immunology, Tel Aviv University, Ramat Aviv 69978, Israel.
The Journal of Biological Chemistry
|July 1, 2005
Summary
Mucin 1 (MUC1) undergoes autoproteolysis, a self-cleavage process within its SEA module, generating alpha and beta subunits. This mechanism is crucial for understanding MUC1 function in adenocarcinomas.
Area of Science:
- Biochemistry
- Molecular Biology
- Cancer Biology
Background:
- Mucin 1 (MUC1) is a glycoprotein overexpressed in human adenocarcinomas.
- MUC1/TM undergoes proteolytic cleavage in its extracellular domain, generating alpha and beta subunits.
- This cleavage occurs within the SEA module, a conserved domain in mucin-like proteins.
Purpose of the Study:
- To elucidate the mechanism of MUC1 proteolysis.
- To investigate the role of the SEA module in MUC1 cleavage.
- To differentiate cleavage patterns between MUC1 isoforms MUC1/X and MUC1/Y.
Main Methods:
- Analysis of MUC1 isoforms MUC1/X and MUC1/Y.
- Site-directed mutagenesis of the MUC1/X serine residue (Ser-63).
- In vitro incubation of purified MUC1/X protein and addition of hydroxylamine.
Main Results:
- MUC1/X undergoes proteolytic cleavage at the same site as MUC1/TM.
- MUC1/Y isoform is not cleaved.
- Mutations of Ser-63 to cysteine or threonine resulted in cleavage, while other mutations did not.
- Purified MUC1/X protein exhibited self-cleavage in vitro.
- Hydroxylamine enhanced MUC1 cleavage, indicating autoproteolysis.
Conclusions:
- MUC1 undergoes autoproteolysis mediated by an N --> O-acyl rearrangement at the cleavage site.
- This mechanism involves hydrolytic resolution of an unstable ester intermediate.
- The SEA module is essential for MUC1 self-cleavage.
- This autoproteolysis mechanism is likely conserved in other SEA module-containing proteins.