A 32-KD GTP-BINDING PROTEIN ASSOCIATED WITH THE CD4-P56LCK AND CD8-P56LCK T-CELL RECEPTOR COMPLEXES

The guanosine triphosphate (GTP)-binding proteins include signal-transducing heterotrimeric G proteins (for example, G(s), G(i)), smaller GTP-binding proteins that function in protein sorting, and the oncogenic protein p21(ras). The T cell receptor complexes CD4-p56lck and CD8-p56lck were found to include a 32- to 33-kilodalton phosphoprotein (p32) that was recognized by an antiserum to a consensus GTP-binding region in G proteins. Immununoprecipitated CD4 and CD8 complexes bound GTP and hydrolyzed it to guanosine diphosphate (GDP). The p32 protein was covalently linked to [alpha-P-32]GTP by ultraviolet photoaffinity labeling. These results demonstrate an interaction between T cell receptor complexes and an intracellular GTP-binding protein.