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A 32-kD GTP-binding protein associated with the CD4-p56lck and CD8-p56lck T cell receptor complexes
1Division of Tumor Immunology, Dana-Farber Cancer Institute, Boston, MA.
Abstract:
The guanosine triphosphate (GTP)-binding proteins include signal-transducing heterotrimeric G proteins (for example, Gs, Gi), smaller GTP-binding proteins that function in protein sorting, and the oncogenic protein p21ras. 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. Immunoprecipitated CD4 and CD8 complexes bound GTP and hydrolyzed it to guanosine diphosphate (GDP). The p32 protein was covalently linked to [alpha-32P]GTP by ultraviolet photoaffinity labeling. These results demonstrate an interaction between T cell receptor complexes and an intracellular GTP-binding protein.
Insights
Researchers discovered a GTP-binding protein (p32) interacting with T cell receptor complexes (CD4 and CD8). This finding reveals a novel link between T cell signaling and intracellular GTP-binding proteins.
Area of Science:
- Immunology
- Molecular Biology
- Cell Signaling
Background:
- Guanosine triphosphate (GTP)-binding proteins are crucial in various cellular processes, including signal transduction and protein sorting.
- T cell receptor (TCR) complexes, such as CD4-p56lck and CD8-p56lck, mediate T cell activation.
- The precise molecular interactions within TCR complexes are still under investigation.
Purpose of the Study:
- To investigate the potential interaction between T cell receptor complexes and intracellular GTP-binding proteins.
- To identify and characterize any associated GTP-binding proteins within CD4 and CD8 complexes.
Main Methods:
- Immunoprecipitation of CD4 and CD8 T cell receptor complexes.
- Detection of associated phosphoproteins using antiserum against GTP-binding regions.
- GTP binding and hydrolysis assays.
- Ultraviolet photoaffinity labeling with [alpha-32P]GTP to identify covalently linked proteins.
Main Results:
- A 32- to 33-kilodalton phosphoprotein (p32) was identified within immunoprecipitated CD4 and CD8 complexes.
- The p32 protein was recognized by an antiserum specific for GTP-binding regions.
- Immunoprecipitated complexes demonstrated the ability to bind and hydrolyze GTP to guanosine diphosphate (GDP).
- Photoaffinity labeling confirmed the covalent linkage of p32 to GTP.
Conclusions:
- T cell receptor complexes (CD4 and CD8) interact with an intracellular GTP-binding protein, identified as p32.
- This interaction suggests a role for GTP-binding proteins in T cell receptor signaling pathways.
- The findings elucidate a novel molecular connection within T cell immunology.