PMID: 20417641 , Related PDB ids: 3G0A, 3G4T, 3G91, 3GA6
Authors:
Li Y, Depontieu FR, Sidney J, Salay TM, Engelhard VH, Hunt DF, Sette A, Topalian SL, Mariuzza RA
Title:
Structural basis for the presentation of tumor-associated MHC class II-restricted phosphopeptides to CD4+ T cells.
Journal:
J Mol Biol. 2010 Jun 18;399(4):596-603. Epub 2010 Apr 24.
Abstract:
Dysregulated protein phosphorylation is a hallmark of malignant transformation. Transformation can generate major histocompatibility complex (MHC)-bound phosphopeptides that are differentially displayed on tumor cells for specific recognition by T cells. To understand how phosphorylation alters the antigenic identity of self-peptides and how MHC class II molecules present phosphopeptides for CD4(+) T-cell recognition, we determined the crystal structure of a phosphopeptide derived from melanoma antigen recognized by T cells-1 (pMART-1), selectively expressed by human melanomas, in complex with HLA-DR1. The structure revealed that the phosphate moiety attached to the serine residue at position P5 of pMART-1 is available for direct interactions with T-cell receptor (TCR) and that the peptide N-terminus adopts an unusual conformation orienting it toward TCR. This structure, combined with measurements of peptide affinity for HLA-DR1 and of peptide-MHC recognition by pMART-1-specific T cells, suggests that TCR recognition is focused on the N-terminal portion of pMART-1. This recognition mode appears to be distinct from that of foreign antigen complexes but is remarkably reminiscent of the way autoreactive TCRs engage self- or altered self-peptides, consistent with the tolerogenic nature of tumor-host immune interactions.