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Human MHC Class II Molecule
MHC class II molecules are expressed exclusively on the surfaces of "antigen-presenting cells" -- including macrophages, dendritic cells, and B cells -- where they serve to stimulate CD4-positive TH-cells, thereby initiating the release of cytokines that regulate other cellular processes associated with immune responses. Animated images of the molecular complexes between 2 human HLA-DR1 molecules and the synthetic polyalanine peptide -- (Ala)13 -- illustrate key structural features of MHC class II molecules and their antigen-binding pockets.
Mouse Moves
1. Animated overview of the HLA-DR1 class II complex with (Ala)13 peptide
2. Examine the peptide-binding pocket formed by a network of anti-parallel β-strands and 2 α-helices from the α1 and β1 domains, illustrated at one point here by a simultaneous trace in N-to-C direction through α1 and β1.
3. View the immunoglobulin folds of the α2 and β2 domains.
4. View the (αβ)2 tetrameric dimer complex with two peptide antigen binding sites.
5. Color coding:
 
  • α1 and α2 = a membrane-distal and  membrane-proximal subunit domains, respectively.
  • β1 and β2 = β membrane-distal and membrane-proximal subunit domains, respectively.
  • Synthetic polyalanine peptide (Ala13) bound to the α1β1 antigen binding pocket of HLA-DR1.
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© Duane W. Sears