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A role for calnexin (IP90) in the assembly of class II MHC molecules

K S Anderson1, P Cresswell

  • 1Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, CT 06510.

The EMBO Journal
|February 1, 1994
PubMed

Insights

Calnexin, an ER protein, binds to Major Histocompatibility Complex (MHC) class II molecules during their assembly. This interaction ensures proper folding and stabilization of MHC class II-invariant chain complexes before their release from the endoplasmic reticulum.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • Major histocompatibility complex (MHC) class II molecules present antigens to T helper cells.
  • MHC class II assembly involves alpha, beta, and invariant (I) chains in the endoplasmic reticulum (ER).
  • The HLA-DR alpha beta I complex forms a nonameric structure.

Purpose of the Study:

  • To investigate the role of calnexin in the intracellular assembly of MHC class II molecules.
  • To determine the timing and nature of calnexin association with MHC class II components.

Main Methods:

  • Analysis of intracellular protein associations using co-immunoprecipitation.
  • Pulse-chase experiments to track protein synthesis and assembly kinetics.
  • Examination of calnexin binding to free MHC class II subunits and partially assembled complexes.

Main Results:

  • Calnexin rapidly associates with newly synthesized MHC class II alpha, beta, and I chains.
  • Calnexin remains bound throughout the nonamer assembly process, until the final dimer addition.
  • Calnexin dissociation correlates with the exit of the assembled MHC class II complex from the ER.

Conclusions:

  • Calnexin acts as a crucial chaperone for MHC class II assembly in the ER.
  • Calnexin stabilizes both individual subunits and intermediate complexes.
  • This chaperone function ensures the integrity of MHC class II molecules before their transport and function.

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