1KJM: Tap-A-Associated Rat Mhc Class I Molecule

Citation:
Abstract
Antigenic peptides are loaded onto class I MHC molecules in the endoplasmic reticulum (ER) by a complex consisting of the MHC class I heavy chain, beta(2)-microglobulin, calreticulin, tapasin, Erp57 (ER60) and the transporter associated with antigen processing (TAP). While most mammalian species transport these peptides into the ER via a single allele of TAP, rats have evolved different TAPs, TAP-A and TAP-B, that are present in different inbred strains. Each TAP delivers a different spectrum of peptides and is associated genetically with distinct subsets of MHC class Ia alleles, but the molecular basis for the conservation (or co-evolution) of the two transporter alleles is unknown. We have determined the crystal structures of a representative of each MHC subset, viz RT1-A(a) and RT1-A1(c), in association with high-affinity nonamer peptides. The structures reveal how the chemical properties of the two different rat MHC F-pockets match those of the corresponding C termini of the peptides, corroborating biochemical data on the rates of peptide-MHC complex assembly. An unusual sequence in RT1-A1(c) leads to a major deviation from the highly conserved beta(3)/alpha(1) loop (residues 40-59) conformation in mouse and human MHC class I structures. This loop change contributes to profound changes in the shape of the A-pocket in the peptide-binding groove and may explain the function of RT1-A1(c) as an inhibitory natural killer cell ligand.
PDB ID: 1KJMDownload
MMDB ID: 71098
PDB Deposition Date: 2001/12/4
Updated in MMDB: 2012/09
Experimental Method:
x-ray diffraction
Resolution: 2.35  Å
Source Organism:
synthetic construct
Similar Structures:
Biological Unit for 1KJM: trimeric; determined by author and by software (PISA)
Molecular Components in 1KJM
Label Count Molecule
Proteins (3 molecules)
1
RT1 Class I Histocompatibility Antigen, AA Alpha Chain, Heavy Chain(Gene symbol: RT1-EC2)
Molecule annotation
1
Beta-2-microglobulin(Gene symbol: B2m)
Molecule annotation
1
B6 Peptide
Molecule annotation
Chemical (1 molecule)
1
1
* Click molecule labels to explore molecular sequence information.

Citing MMDB
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