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The Mac-2 antigen is a galactose-specific lectin that binds IgE
B J Cherayil1, S J Weiner, S Pillai
1Molecular Immunology Laboratory, Cancer Center of the Massachusetts General Hospital, Boston, Massachusetts.
The Journal of Experimental Medicine
|December 1, 1989
Summary
Researchers cloned the Mac-2 antigen (also known as carbohydrate-binding protein 35), a macrophage surface marker. This lectin binds carbohydrates and IgE, and surprisingly, is found extracellularly despite lacking a signal peptide.
Area of Science:
- Molecular Biology
- Immunology
- Cell Biology
Background:
- Mac-2 antigen is a surface marker highly expressed by macrophages.
- The Mac-2 antigen is identical to carbohydrate-binding protein 35 (lectin).
- It shows homology to a rat IgE-binding protein.
Purpose of the Study:
- To clone the cDNA encoding the Mac-2 antigen.
- To investigate the properties and localization of the Mac-2 protein.
Main Methods:
- Immunoscreening of a lambda gt11 expression library.
- Nucleotide sequencing of the cloned cDNA.
- In vitro protein synthesis and binding assays.
- Pulse-chase analysis and subcellular fractionation.
Main Results:
- The cDNA sequence for Mac-2 antigen was determined and found identical to carbohydrate-binding protein 35.
- In vitro synthesized Mac-2 protein exhibited carbohydrate and IgE binding.
- Mac-2 protein was localized to the cytosol and surprisingly, the extracellular medium.
- An alternatively spliced cDNA potentially encoding an extended Mac-2 protein was identified.
Conclusions:
- The Mac-2 protein (carbohydrate-binding protein 35) possesses lectin and IgE-binding capabilities.
- The extracellular localization of Mac-2 is unexpected given its lack of a signal peptide.
- Further research is needed to clarify the mechanism of extracellular Mac-2 secretion and its functional implications.