Bound peptide-dependent thermal stability of major histocompatibility complex class II molecule I-Ek

Biochemistry. 2004 Aug 10;43(31):10186-91. doi: 10.1021/bi049838f.

Abstract

We used differential scanning calorimetry to study the thermal denaturation of murine major histocompatibility complex class II, I-E(k), accommodating hemoglobin (Hb) peptide mutants possessing a single amino acid substitution of the chemically conserved amino acids buried in the I-Ek pocket (positions 71 and 73) and exposed to the solvent (position 72). All of the I-Ek-Hb(mut) molecules exhibited greater thermal stability at pH 5.5 than at pH 7.4, as for the I-Ek-Hb(wt) molecule, which can explain the peptide exchange function of MHC II. The thermal stability was strongly dependent on the bound peptide sequences; the I-Ek-Hb(mut) molecules were less stable than the I-Ek-Hb(wt) molecules, in good correlation with the relative affinity of each peptide for I-Ek. This supports the notion that the bound peptide is part of the completely folded MHC II molecule. The thermodynamic parameters for I-Ek-Hb(mut) folding can explain the thermodynamic origin of the stability difference, in correlation with the crystal structural analysis, and the limited contributions of the residues to the overall conformation of the I-Ek-peptide complex. We found a linear relationship between the denaturation temperature and the calorimetric enthalpy change. Thus, although the MHC II-peptide complex could have a diverse thermal stability spectrum, depending on the amino acid sequences of the bound peptides, the conformational perturbations are limited. The variations in the MHC II-peptide complex stability would function in antigen recognition by the T cell receptor by affecting the stability of the MHC II-peptide-T cell receptor ternary complex.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigen Presentation
  • Aspartic Acid / genetics
  • CD4-Positive T-Lymphocytes / metabolism
  • Calorimetry, Differential Scanning
  • Chromatography, Gel
  • Glutamic Acid / genetics
  • Hemoglobins / chemistry
  • Hemoglobins / genetics
  • Hemoglobins / metabolism
  • Histocompatibility Antigens Class II / chemistry*
  • Histocompatibility Antigens Class II / genetics
  • Histocompatibility Antigens Class II / metabolism*
  • Hydrogen-Ion Concentration
  • Mice
  • Mutagenesis, Site-Directed
  • Peptide Fragments / chemistry*
  • Peptide Fragments / genetics
  • Peptide Fragments / metabolism*
  • Protein Binding
  • Protein Conformation
  • Protein Denaturation
  • Thermodynamics*

Substances

  • Hemoglobins
  • Histocompatibility Antigens Class II
  • I-E-antigen
  • Peptide Fragments
  • Aspartic Acid
  • Glutamic Acid