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Post-translational modifications of human interleukin-6.
U Santhanam1, J Ghrayeb, P B Sehgal
1Rockefeller University, New York, New York 10021.
Archives of Biochemistry and Biophysics
|October 1, 1989
Summary
Interleukin-6 (IL-6) protein modification involves distinct O- and N-glycosylation pathways, with phosphorylation occurring before secretion. These findings offer insights into post-translational protein modifications in human cells.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Interleukin-6 (IL-6) is secreted by human fibroblasts upon induction with IL-1 or TNF.
- Previously identified IL-6 forms include six phosphoglycoproteins (23-30 kDa).
Purpose of the Study:
- To elucidate the glycosylation patterns of IL-6.
- To investigate the protein modification pathways of IL-6 during biosynthesis.
- To identify additional IL-6 species and understand their implications.
Main Methods:
- Metabolic labeling
- Glycosidase digestion
- Lectin chromatography
- Pulse-chase experiments
- Immunoprecipitation
- Immunoblotting
- Immunoaffinity chromatography
Main Results:
- IL-6 species (23-25 kDa) are O-glycosylated; species (28-30 kDa) are both O- and N-glycosylated.
- Two distinct pathways exist for IL-6 polypeptide modification: O-glycosylation and N-/O-glycosylation, both followed by phosphorylation.
- Tunicamycin treatment results in exclusive O-glycosylation, while cycloheximide favors N-/O-glycosylation.
- Additional IL-6 species (17-19 kDa and 45 kDa) were detected, suggesting further modifications.
Conclusions:
- IL-6 biosynthesis involves distinct O- and N-glycosylation pathways, influencing its final structure.
- These findings provide a model for studying post-translational protein modifications.
- The identified pathways may reconcile conflicting descriptions of IL-6 structure.