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Published on: February 28, 2019
Dynamics of major histocompatibility complex class I association with the human peptide-loading complex
Michaela S Panter1, Ankur Jain, Ralf M Leonhardt
1Department of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA.
The human peptide-loading complex (PLC) composition varies, with a critical TAP/tapasin ratio of 1:2. Its MHC I association dynamically adapts to peptide availability, crucial for antigen presentation.
Area of Science:
- Immunology
- Molecular Biology
- Structural Biology
Background:
- The human peptide-loading complex (PLC) is essential for major histocompatibility complex class I (MHC I) antigen presentation.
- The precise stoichiometry of PLC components, particularly the ratios of transporter associated with antigen processing (TAP), MHC I, and tapasin, remains incompletely understood.
- Understanding PLC composition is critical for accurate modeling and comprehending MHC I peptide loading quality control.
Purpose of the Study:
- To characterize the stoichiometry of the human PLC using integrated biophysical and biochemical methods.
- To determine the ratios of TAP, tapasin, and MHC I within the PLC.
- To investigate how PLC composition is influenced by peptide supply and MHC I allelic variations.
Main Methods:
- Single-molecule pulldown (SiMPull) assays to determine TAP/tapasin ratios.
- Mutational analyses and co-precipitation studies to assess tapasin/MHC I ratios.
- Inhibition of proteasome or TAP-mediated transport to modulate peptide supply.
Main Results:
- A consistent TAP/tapasin ratio of 1:2 was determined for the human PLC.
- The tapasin/MHC I ratio was found to be variable, with both 2:1 and 2:2 complexes observed.
- MHC I association with PLC increased under conditions of reduced peptide supply, such as proteasome inhibition or TAP blockade.
Conclusions:
- The composition of the human PLC is not fixed and can dynamically adapt to changes in peptide availability.
- These compositional shifts are relevant during viral infections when peptide supply is altered.
- The findings enhance understanding of MHC I peptide loading quality control and provide a basis for structural and functional PLC modeling.
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