We compared the conformation of empty and peptide-loaded class I major histocompatibility complex (MHC) molecules at the cell surface. Molecular conformations were analyzed by fluorescence resonance energy transfer (FRET) between fluorescent-labeled Fab fragments bound to the alpha 2 domain of the MHC heavy chain and fluorescent-labeled Fab fragments bound to beta 2-microglobulin. No FRET was found between Fab fragments bound to empty H-2Kb, but FRET was detected when empty H-2Kb molecules were loaded with peptide. The magnitude of FRET depended on the sequence of the peptide used. The results imply that empty H-2Kb molecules are in a relatively extended conformation, and that this conformation becomes more compact when peptide is bound. These changes, which are reflected in peptide-dependent binding of monoclonal antibodies, affect the surfaces of MHC molecules available for contact with T cell receptors and hence may influence T cell-receptor recognition of MHC molecules.
Analysis of the structure of empty and peptide-loaded major histocompatibility complex molecules at the cell surface.
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B Catipović, G Talluri, J Oh, T Wei, X M Su, T E Johansen, M Edidin, J P Schneck; Analysis of the structure of empty and peptide-loaded major histocompatibility complex molecules at the cell surface.. J Exp Med 1 November 1994; 180 (5): 1753–1761. doi: https://doi.org/10.1084/jem.180.5.1753
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