Journal of Experimental Medicine, Vol 176, 887-891, Copyright © 1992 by Rockefeller University Press

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A 68-kD GTP-binding protein associated with the T cell receptor complex

T Ohmura, A Sakata and K Onoue
Department of Immunology, Kumamoto University School of Medicine, Japan.

The identity of the guanine nucleotide-binding protein (G protein) involved in T cell activation pathways remains unclear. We identified a 68-kD GTP-binding protein associated with the T cell receptor (TCR)/CD3 complex using immunoprecipitation and GTP-affinity labeling techniques. Proteins coimmunoprecipitated with the TCR/CD3 complex in digitonin lysate of a human leukemic T cell line, MOLT 16, were incubated with alpha-[32P]GTP and irradiated with ultraviolet rays to covalently link the labeled GTP to GTP-binding proteins. They were then analyzed by electrophoresis. The 68-kD protein exhibited nucleotide specificity for GTP-binding and was insensitive to cholera and pertussis toxins. The 68- kD GTP-binding protein could be coimmunoprecipitated with the TCR/CD3 complex but not with other surface molecules such as major histocompatibility complex class I and lymphocyte function associated- 1, which do not cause rapid Ca2+ mobilization. These suggest that the 68-kD GTP-binding protein is specifically associated with the TCR/CD3 complex.
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