Abstract
Peptide binding reactions of class II MHC proteins exhibit unusual kinetics, with extremely slow apparent rate constants for the overall association (< 100 M-1 s-1) and dissociation (< 10-5 s-1) processes. Various linear and branched pathways have been proposed to account for these data. Using fluorescence resonance energy transfer between tryptophan residues in the MHC peptide binding site and aminocoumarin-labeled peptides, we measured real-time kinetics of peptide binding to empty class II MHC proteins. Our experiments identified an obligate intermediate in the binding reaction. The observed kinetics were consistent with a binding mechanism that involves an initial bimolecular binding step followed by a slow unimolecular conformational change. The same mechanism is observed for different peptide antigens. In addition, we noted a reversible inactivation of the empty MHC protein that competes with productive binding. The implications of this kinetic mechanism for intracellular antigen presentation pathways are discussed.
Original language | English (US) |
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Pages (from-to) | 3751-3762 |
Number of pages | 12 |
Journal | Biochemistry |
Volume | 39 |
Issue number | 13 |
DOIs | |
State | Published - Apr 4 2000 |
ASJC Scopus subject areas
- Biochemistry