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Molecular basis of MHC I quality control in the peptide loading complex
Alexander Domnick1, Christian Winter1, Lukas Sušac1
1Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438, Frankfurt am Main, Germany.
The peptide loading complex (PLC) stabilizes peptide-receptive Major Histocompatibility Complex class I (MHC I) molecules. Glycan processing and peptide loading are coupled, initiating adaptive immunity.
Area of Science:
- Immunology
- Molecular Biology
- Structural Biology
Background:
- Major histocompatibility complex class I (MHC I) molecules are crucial for adaptive immunity.
- MHC I assembly, epitope selection, and antigen presentation are regulated by the MHC I glycan and associated proteins.
- The precise integration of these processes remains unclear.
Purpose of the Study:
- To elucidate the multi-chaperone-client interaction network of the peptide loading complex (PLC).
- To determine the structure of the PLC editing module.
- To understand the interplay between MHC I glycan processing and peptide loading.
Main Methods:
- Cryogenic electron microscopy (cryo-EM) at 3.7 Å resolution.
- Epitope-proofreading studies.
- Analysis of PLC in a near-native lipid environment.
Main Results:
- The structure of the PLC editing module was determined.
- Peptide-receptive MHC I molecules are stabilized by chaperone interactions, including the calreticulin-engulfed mono-glucosylated MHC I glycan.
- Glycan processing by α-glucosidase II is contingent on the loading of optimal epitopes.
Conclusions:
- Allosteric coupling exists between peptide-MHC I assembly and glycan processing.
- This communication regulates the initiation of adaptive immune responses.
- The findings offer a model for endoplasmic reticulum quality control mechanisms.
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