Allosteric changes in the TCR/CD3 structure upon interaction with extra- or intra-cellular ligands.

Area of Science:

• Immunology
• Molecular Biology
• Cellular Signaling

Background:

• T-cell activation relies on T-cell receptor (TCR) interactions with peptide-MHC complexes.
• The low avidity of TCR-pMHC binding necessitates specific mechanisms for T-cell activation.
• Existing models include conformational change, aggregation, kinetic segregation, sequential interaction, and permissive geometry.

Purpose of the Study:

• To experimentally differentiate between the TCR aggregation and TCR conformational change models of T-cell activation.
• To investigate structural alterations in TCR/CD3 complexes upon ligand binding.

Main Methods:

• TCR capture ELISA using solubilized TCR molecules from T cells.
• Size-fractionation of TCR/CD3/co-receptor complexes from naïve and activated T cells.
• Analysis of structural changes in CD3 epsilon and TCR beta FG loop regions.

Main Results:

• Ligand-TCR interaction induces conformational changes in the CD3 epsilon cytoplasmic tail and TCR beta FG loop.
• TCR/CD3/co-receptor complexes exist as dimers or tetramers, with no monomers or multimers detected.
• Structural changes in CD3 epsilon are linked to T-cell activation.

Conclusions:

• Ligand binding triggers conformational changes in the CD3 epsilon tail, initiating T-cell activation.
• Intracellular interactions with the CD3 epsilon tail may regulate T-cell activation by dissociating co-receptors.
• T-cell activation occurs within dimers or tetramers of TCR/CD3/co-receptor complexes bound to peptide-MHC.