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Related Experiment Videos

Mutant MHC class I molecules define interactions between components of the peptide-loading complex.

Marie-Eve Paquet1, David B Williams

  • 1Department of Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.

International Immunology
|April 6, 2002
PubMed
Summary

Class I histocompatibility molecules require tapasin for optimal assembly with the peptide transporter (TAP). Mutations affecting tapasin interaction impact cell surface expression and transport, but peptide loading is still possible, suggesting tapasin is not strictly essential.

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Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • Class I histocompatibility molecules are crucial for immune response, assembling in the endoplasmic reticulum (ER) with chaperones.
  • Peptide loading onto Class I molecules involves a complex including the transporter associated with antigen processing (TAP) and tapasin.

Purpose of the Study:

  • To investigate the physical organization of the ER peptide-loading complex.
  • To determine the role of specific H-2Dd heavy chain mutations in complex assembly and function.

Main Methods:

  • Generation of H-2Dd heavy chain mutants with specific amino acid alterations.
  • Assessment of mutant association with components of the peptide-loading complex (tapasin, TAP, CRT).
  • Analysis of cell-surface expression, intracellular transport, and peptide loading.

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Main Results:

  • Mutations between amino acids 122-136 and at position 222 disrupted tapasin interaction, leading to simultaneous loss of TAP association.
  • Loss of tapasin interaction resulted in reduced cell-surface expression and altered intracellular transport.
  • Most mutants retained significant peptide loading capacity, indicating tapasin is not essential for this process.
  • Mutants lacking tapasin interaction maintained normal association with calreticulin (CRT).

Conclusions:

  • Tapasin acts as a bridge between Class I molecules and TAP, crucial for optimal assembly.
  • The ER peptide-loading complex organization can differ between Class I molecules, as evidenced by H-2Dd's interaction with CRT.
  • While tapasin promotes peptide loading, it is not strictly required for Class I molecule function.