Cutting edge: Evidence for a dynamically driven T cell signaling mechanism

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• T cells recognize antigens via the T cell receptor (TCR) complex, which binds peptide-MHC (pMHC) complexes on antigen-presenting cells (APCs).
• The precise molecular mechanisms by which TCR-pMHC engagement initiates T cell signaling remain incompletely understood, with proposed roles for altered TCR conformation, subunit interactions, and mechanical forces.

Purpose of the Study:

• To investigate the structural and dynamic consequences of TCR-pMHC ligation.
• To elucidate the potential role of TCR conformational changes in initiating T cell activation.

Main Methods:

• Employed hydrogen/deuterium exchange mass spectrometry (HDX-MS) to probe TCR structural dynamics upon pMHC binding.
• Utilized computational modeling to analyze dynamic coupling within the TCR complex.

Main Results:

• TCR ligation by pMHC induced global rigidification of the TCR structure.
• This global stiffening enhances interactions with neighboring proteins and stabilizes existing complexes, particularly affecting regions involved in lateral associations and signaling.
• Computational analysis revealed dynamic coupling between TCR constant and variable domains, which is reduced upon ligation.

Conclusions:

• TCR triggering may involve a dynamically driven, allosteric mechanism, where global rigidification upon ligand binding alters TCR function.
• These findings provide new insights into the structural basis of T cell activation and antigen recognition.