Peptide-induced conformational changes in class I molecules. Direct detection by flow cytometry.
Activation of a T cell in response to peptide bound to class I MHC occurs by the sum of interactions across the area of contact between the TCR, the peptide, and class I MHC. It has been observed recently that substitution of the peptide residue at a position that is not accessible from the exterior of the class I molecule modulates T cell responses, raising the possibility that there may be indirect structural effects in the peptide-class I complex as a consequence of peptide binding. This report describes the use of mAbs to probe the conformation of the alpha 1 and alpha 2 domains of the mouse class I molecule Kb when bound to ovalbumin peptide and a panel of 19 peptide analogues that differ at position 2 (P2). By crystallographic data, side chains of this position are buried in the Ag binding cleft and have no direct access to the TCR. Substitution of position 2 results in a measurable change in conformation of the class I molecule, a change that correlates with the ability to stimulate T cells. This leads to a model that T cell activation by the peptide-class I complex may occur in three ways: 1) direct interaction of the TCR with the class I heavy chain, 2) direct interaction of the TCR with solvent-accessible peptide side chains, and 3) indirect interaction of peptide with TCR mediated via conformational perturbations in the class I complex.
Rohren
E M
EM
Department of Immunology, Mayo Foundation, Rochester, MN 55905.
McCormick
D J
DJ
Pease
L R
LR
D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000737:chemistry* / Q000378:metabolism; D008213:Lymphocyte Activation; D051379:Mice; D008969:Molecular Sequence Data; D010047:Ovalbumin / Q000378:metabolism; D010455:Peptides / Q000378:metabolism*; D011487:Protein Conformation; D013601:T-Lymphocytes / Q000276:immunology*
D015395:Histocompatibility Antigens Class I; D010455:Peptides; D010047:Ovalbumin