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Misfolded major histocompatibility complex class I molecules accumulate in an expanded ER-Golgi intermediate
G Raposo1, H M van Santen, R Leijendekker
1Universiteit Utrecht, Faculty of Medicine, Department of Cell Biology, The Netherlands.
The Journal of Cell Biology
|December 1, 1995
Summary
Misfolded HLA-B27 proteins accumulate in the endoplasmic reticulum-Golgi intermediate compartment. Ubiquitin tagging suggests these proteins are degraded via a non-lysosomal pathway in thymic epithelial cells.
Area of Science:
- Immunology
- Cell Biology
- Protein Degradation
Background:
- Misfolded membrane proteins are rapidly degraded in the endoplasmic reticulum (ER).
- The precise location and mechanisms of this degradation remain largely unknown.
- MHC class I molecules require peptide binding for proper folding and ER exit.
Purpose of the Study:
- To investigate the degradation pathway of misfolded membrane proteins, specifically HLA-B27.
- To identify the cellular compartment where misfolded HLA-B27 accumulates.
- To elucidate the mechanism of degradation for these misfolded proteins.
Main Methods:
- Utilized mice transgenic for HLA-B27 on a TAP1-deficient background.
- Employed immunoelectron microscopy to visualize misfolded HLA-B27 molecules.
- Assessed protein conformation, carbohydrate modifications, and association with degradation machinery.
Main Results:
- Withholding TAP-dependent peptides caused misfolded HLA-B27 to accumulate in the ER.
- Misfolded HLA-B27 molecules failed to undergo Golgi-associated modifications.
- Accumulation occurred in an ER-Golgi intermediate compartment containing ubiquitin and ubiquitin-conjugating enzymes.
- This suggests a non-lysosomal degradation pathway.
Conclusions:
- Misfolded HLA-B27 molecules accumulate in an ER-Golgi intermediate compartment.
- The presence of ubiquitin indicates a non-lysosomal degradation pathway for these misfolded proteins.
- This study provides insights into the cellular mechanisms for clearing misfolded membrane proteins.