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αβ T cell receptors (TCRs) are genetically restricted to corecognize peptide antigens bound to self-major histocompatibility complex (pMHC) molecules; however, the basis for this MHC specificity remains unclear. Despite the current dogma, evaluation of the TCR-pMHC-l structural database shows that the nongermline-encoded complementaritydetermining region (CDR)-3 loops often contact the MHC-l, and the germline-encoded CDR1 and -2 loops frequently participate in peptide-mediated interactions. Nevertheless, different TCR5 adopt a roughly conserved docking mode over the pMHC-l, in which three MHC-I residues (65, 69, and 155) are invariably contacted by the TCR in one way or another. Nonetheless, the impact of mutations at these three positions, either individually or together, was not uniformly detrimental to TCR recognition of pHLA.B*0801 or pHLAB*35O8. Moreover, when TCR-pMHC-I recognition was impaired, this could be partially restored by expression of the CD8 coreceptor. The structure of a TCR-pMHC-I complex in which these three (65,69, and 155) MHC-l positions were all mutated resulted in shifting of the TCR footprint relative to the cognate complex and formation of compensatory interactions. Collectively, our findings reveal the inherent adaptability of the TCR in maintaining peptide recognition while accommodating changes to the central docking site on the pMHC-I. [ABSTRACT FROM AUTHOR]

The CD3∊γ heterodimer is essential for expression and function of the T cell receptor. The crystal structure of the human CD3∊γ heterodimer is described to 2.1-Å resolution complexed with OKT3, a therapeutic mAb that not only activates and tolerizes mature T cells but also induces regulatory T cells. The mode of CD3∊γ dimerization provides a general structural basis for CD3 assembly and maps candidate T cell antigen receptor docking sites, including a duplicated linear region rich in acidic residues that is unique to human CD3∊. OKT3 binds to an atypically small area of CD3t and has a low affinity for the isolated CD3∊γ heterodimer. The structure of the OKT3/CD3∊γ complex has implications for T cell signaling and therapeutic design. [ABSTRACT FROM AUTHOR]

The CD3 epsilon gamma heterodimer is essential for expression and function of the T cell receptor. The crystal structure of the human CD3 epsilon gamma heterodimer is described to 2.1-A resolution complexed with OKT3, a therapeutic mAb that not only activates and tolerizes mature T cells but also induces regulatory T cells. The mode of CD3 epsilon gamma dimerization provides a general structural basis for CD3 assembly and maps candidate T cell antigen receptor docking sites, including a duplicated linear region rich in acidic residues that is unique to human CD3 epsilon. OKT3 binds to an atypically small area of CD3 epsilon and has a low affinity for the isolated CD3 epsilon gamma heterodimer. The structure of the OKT3/CD3 epsilon gamma complex has implications for T cell signaling and therapeutic design.