Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 42, Pages 16639-16644Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0707061104
Keywords
conformational changes; T cell receptor-ligand; interactions; FRET; stopped flow; induced fit
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Thermodynamics and kinetics of the interaction between T cell receptor specific for cytomegalovirus pepticle (TCRCMV) and its specific ligand, pp65-HLA-A*0201 complex, were studied by surface plasmon resonance and stopped-flow methods. In the latter measurements, fluorescence resonance energy transfer (FRET) between fluorescently labeled reactants was used. Thermodynamic data derived from surface plasmon resonance measurements suggest that the complex formation is driven by both favorable enthalpy and entropy. Two reaction phases were resolved by the stopped-flow measurements. The rate constant of the first step was calculated to be close to the diffusion-controlled limit rate (3-10(5) to 10(6) M-1.S-1), whereas the second step's reaction rate was found to be concentration independent and relatively slow (2-4 s(-1) at 25 degrees C). These findings strongly suggest that the interactions between the TCR and its ligand, the peptide-MHC complex, proceed by a two-step mechanism, in which the second step is an induced-fit process, rate determining for antigen recognition by TCR.
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