Crystal Structure of the V α Domain of a T Cell Antigen Receptor

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Abstract
The crystal structure of the Vα domain of a T cell antigen receptor (TCR) was determined at a resolution of 2.2 angstroms. This structure represents an immunoglobulin topology set different from those previously described. A switch in a polypeptide strand from one β sheet to the other enables a pair of Vα homodimers to pack together to form a tetramer, such that the homodimers are parallel to each other and all hypervariable loops face in one direction. On the basis of the observed mode of Vα association, a model of an (αβ)2 TCR tetramer can be positioned relative to the major histocompatibility complex class II (αβ)2 tetramer with the third hypervariable loop of Vα over the amino-terminal portion of the antigenic peptide and the corresponding loop of Vβ over its carboxyl-terminal residues. TCR dimerization that is mediated by the α chain may contribute to the coupling of antigen recognition to signal transduction during T cell activation.