Outsize peptides bulge out of the groove.

The highly polymorphic MHC class I molecules are a central part of the cellular immune response to viruses. They present peptides, processed from viral proteins synthesized in the cytosol, to CD8+ cytotoxic T cells (CTL) that eliminate virus-infected cells. Here, Christopher Thorpe, describes the recent flurry of high resolution X-ray crystallographic structures that has allowed a general model of MHC-peptide interactions to be developed.