Pre-T cell receptors topologically sample self-ligands during thymocyte β-selection.

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• Thymocyte development involves self-discrimination, a crucial process mediated by T cell receptors (TCRs).
• The precise molecular mechanisms of pre-TCR and TCR interactions during this process remain incompletely understood.

Purpose of the Study:

• To elucidate the distinct binding modes of pre-TCRs and alpha-beta TCRs to MHC molecules.
• To understand how these distinct interactions influence T cell repertoire development and selection.

Main Methods:

• X-ray crystallography was employed to determine the high-resolution structures of pre-TCR and TCR interactions.
• Comparative structural analysis of pre-TCR and TCR binding interfaces.

Main Results:

• The pre-TCR utilizes a "horizontal" docking mechanism, engaging the MHC α2-helix with its Vβ domain.
• Alpha-beta TCRs employ a "vertical" head-to-head binding mode, utilizing all six CDR loops to recognize peptide-MHC complexes.
• The pre-TCR's binding mode facilitates sampling of the peptide's C-terminal region, setting the stage for canonical alpha-beta TCR docking.

Conclusions:

• The pre-TCR's distinct binding strategy allows for broader β-chain repertoire diversification by preventing germline CDR1β and CDR2β interactions with MHC.
• This sequential attunement of recognition logic by receptor subunits is critical for refining the T cell repertoire before alpha-beta TCR-mediated selection.