ASSEMBLY, SPECIFIC BINDING, AND CRYSTALLIZATION OF A HUMAN TCR-ALPHA-BETA WITH AN ANTIGENIC TAX PEPTIDE FROM HUMAN T-LYMPHOTROPIC VIRUS TYPE-1 AND THE CLASS-I MHC MOLECULE HLA-A2

T lymphocytes use TCR-alpha beta to bind and to recognize complexes of antigenic peptides bound to MHC proteins located at the surface of AP Cs, We have assembled and crystallized this intercellular complex of T CR/peptide/MHC from soluble human TCR-alpha beta and soluble peptide/H LA-A2 complexes. The soluble TCR-alpha beta binds specifically to its in vivo ligand, the complex of HLA-AZ, and a peptide from the Tax prot ein of human T lymphotropic virus type 1. The soluble TCR also binds i n vitro to an altered peptide ligand, which appears to be a partial ag onist in T cell assays as determined by its ability to elicit differen t cytolytic and lymphokine secretion responses, Heterodimerization and the antigenic specificity of the TCR do not require its interchain di sulfide bond, transmembrane segments, or glycosylations, Crystals of t he TCR/peptide/HLA-A2 complex diffract x-rays, providing the means to study in atomic detail the mechanism of Ag-specific cell-cell recognit ion between T cells and target cells.