1k8d

File:1k8d.jpg

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1k8d, resolution 2.30Å
Gene:	Q9 (Mus musculus)
Coordinates:	save as pdb, mmCIF, xml

crystal structure of the non-classical MHC class Ib Qa-2 complexed with a self peptide

Overview

BACKGROUND: Qa-2 is a nonclassical MHC Ib antigen, which has been implicated in both innate and adaptive immune responses, as well as embryonic development. Qa-2 has an unusual peptide binding specificity in that it requires two dominant C-terminal anchor residues and is capable of associating with a substantially more diverse array of peptide sequences than other nonclassical MHC. RESULTS: We have determined the crystal structure, to 2.3 A, of the Q9 gene of murine Qa-2 complexed with a self-peptide derived from the L19 ribosomal protein, which is abundant in the pool of peptides eluted from the Q9 groove. The 9 amino acid peptide is bound high in a shallow, hydrophobic binding groove of Q9, which is missing a C pocket. The peptide makes few specific contacts and exhibits extremely poor shape complementarity to the MHC groove, which facilitates the presentation of a degenerate array of sequences. The L19 peptide is in a centrally bulged conformation that is stabilized by intramolecular interactions from the invariant P7 histidine anchor residue and by a hydrophobic core of preferred secondary anchor residues that have minimal interaction with the MHC. CONCLUSIONS: Unexpectedly, the preferred secondary peptide residues that exhibit tenuous contact with Q9 contribute significantly to the overall stability of the peptide-MHC complex. The structure of this complex implies a "conformational" selection by Q9 for peptide residues that optimally stabilize the large bulge rather than making intimate contact with the MHC pockets.

About this Structure

1K8D is a Protein complex structure of sequences from Mus musculus. Full crystallographic information is available from OCA.

Reference

Promiscuous antigen presentation by the nonclassical MHC Ib Qa-2 is enabled by a shallow, hydrophobic groove and self-stabilized peptide conformation., He X, Tabaczewski P, Ho J, Stroynowski I, Garcia KC, Structure. 2001 Dec;9(12):1213-24. PMID:11738047

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