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In Vitro Ubiquitination and Deubiquitination Assays of Nucleosomal Histones
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The HLA-DRalpha chain is modified by polyubiquitination.

Nicolas Lapaque1, Martin Jahnke, John Trowsdale

  • 1Division of Immunology, Department of Pathology, University of Cambridge, Cambridge CB2 1QP, United Kingdom.

The Journal of Biological Chemistry
|January 2, 2009
PubMed
Summary

Ubiquitination regulates major histocompatibility complex class II (MHC II) localization. Lysine 225 on DRbeta and lysine 219 on DRalpha are critical for MHC II ubiquitination by MARCH ligases.

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Evaluation of Substrate Ubiquitylation by E3 Ubiquitin-ligase in Mammalian Cell Lysates

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Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • Ubiquitination is a key post-translational modification regulating protein function and localization.
  • Major Histocompatibility Complex class II (MHC II) molecules are crucial for adaptive immunity, presenting antigens to T cells.
  • The localization and stability of MHC II are tightly controlled, involving ubiquitination pathways.

Purpose of the Study:

  • To investigate the specific sites and mechanisms of ubiquitination on the HLA-DR heterodimer.
  • To identify the roles of specific lysine residues in the cytoplasmic tails of DRalpha and DRbeta in ubiquitination.
  • To understand how E3 ligases MARCH I and MARCH VIII modify HLA-DR.

Main Methods:

  • Site-directed mutagenesis of lysine residues in the DRalpha and DRbeta cytoplasmic tails.
  • Analysis of ubiquitination status of wild-type and mutant HLA-DR molecules.
  • Western blotting to detect ubiquitination and identify modified lysine residues.

Main Results:

  • Lysine 225 in the DRbeta cytoplasmic tail is essential for its ubiquitination, while other residues are dispensable.
  • Lysine 219 in the DRalpha cytoplasmic tail is also essential for its ubiquitination.
  • DRbeta undergoes more extensive ubiquitination than DRalpha, with specific features of the DRalpha tail limiting modification extent.

Conclusions:

  • Specific lysine residues (DRbeta-225 and DRalpha-219) are critical for HLA-DR ubiquitination.
  • Differential ubiquitination of DRalpha and DRbeta chains by MARCH ligases influences MHC II regulation.
  • Understanding these ubiquitination sites provides insights into the precise control of MHC II surface expression and function.