MHC Class I Molecule

MHC class I molecules are expressed on the surfaces of most cells and are recognized by CD8-positive cytotoxic T_C-cells, an essential step for initiating the elimination of virally infected cells by T_C-cell-mediated lysis. Below is an image of the molecular complex between a soluble fragment of murine H-2K^b and a 9-amino-acid nucleoprotein peptide of Sendai Virus (SEV-9).

2vab.pdb

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1)	of the extracellular domains of the H-2K^b (αβ₂m) heterodimer
2)	formed by a network of anti-parallel ;β-strands and 2 α-helices, traced at one point here in the N-to-C direction, starting in α₁ and ending in α₂.
3)	of SEV-9 peptide binding to the α₁α₂ membrane-distal domains of H-2K^b. Note the positions of the 9 H₂O molecules.
4)	exposing the interior positions of 9 H₂O molecules that effectively form the "glue" that stabilizes the peptide and MHC pocket interaction.
5)	the α₃ membrane-proximal domain immunoglobulin fold.
6)	β₂m subunit immunoglobulin fold.
Color coding:
α₁, α₂ , and α₃ = a subunit domains of H-2K^b β₂m = β-2 microglobulin subunit O₂ atoms of H₂O molecules (the H atoms are not visible) SEV-9 = Sendai Virus nucleoprotein peptide (Phe-Ala-Pro-Gly-Asn-Tyr-Pro-Ala-Leu) bound to the α₁,α₂ antigen binding pocket of H-2K^b.


	Overview of MHC class I three-dimensional structure.
	Animation of dual peptide binding by one MHC class I molecule.
	Overview of MHC class II three-dimensional structure.
	Animation of MHC class II domain structure.