We identify and consider some characteristics of a peptide antagonist for the Ag-specific receptor on 2C cells (the 2C TCR). The peptide, GNYSFYAL (called GNY), binds to H-2Kb, and a very high-resolution crystal structure of the GNY-Kb complex at 1.35 Å is described. Although the GNY peptide does not bind to Ld, the potency of GNY-Kb as an antagonist is evident from its ability to specifically inhibit 2C TCR-mediated reactions to an allogenic agonist complex (QLSPFPFDL-Ld), as well as to a syngeneic agonist complex (SIYRYYGL-Kb). The crystal structure and the activities of alanine-substituted peptide variants point to the properties of the peptide P4 side chain and the conformation of the Tyr-P6 side chain as the structural determinants of GNYSFYAL antagonist activity.

A new international regime could stop nations before they enter the proliferation “red zone.”

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