Crystal structure of a superantigen bound to the high-affinity, zinc-dependent site on MHC class II.
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Li Y, Li H, Dimasi N, McCormick JK, Martin R, Schuck P, Schlievert PM, Mariuzza RA
Crystal structure of a superantigen bound to the high-affinity, zinc-dependent site on MHC class II.
Immunity. 2001 Jan;14(1):93-104.
- PubMed ID
- 11163233 [ View in PubMed]
- Abstract
MHC class II molecules possess two binding sites for bacterial superantigens (SAGs): a low-affinity site on the alpha chain and a high-affinity, zinc-dependent site on the beta chain. Only the former has been defined crystallographically. We report the structure of streptococcal pyrogenic exotoxin C (SPE-C) complexed with HLA-DR2a (DRA*0101, DRB5*0101) bearing a self-peptide from myelin basic protein (MBP). SPE-C binds the beta chain through a zinc bridge that links the SAG and class II molecules. Surprisingly, SPE-C also makes extensive contacts with the MBP peptide, such that peptide accounts for one third of the surface area of the MHC molecule buried in the complex, similar to TCR-peptide/MHC complexes. Thus, SPE-C may optimize T cell responses by mimicking the peptide dependence of conventional antigen presentation and recognition.