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Partial agonist/antagonist mouse interleukin-2 proteins indicate that a third component of the receptor complex
S M Zurawski1, J L Imler, G Zurawski
1Department of Molecular Biology, DNAX Research Institute, Palo Alto, CA 94304-1104.
Abstract:
Some mouse interleukin-2 (mIL-2) proteins with substitutions at residue Gln141 are unable to trigger a maximal biological response. The Asp141 protein induces the lowest maximal response. The Asp141 protein can weakly antagonize the biological activity of mIL-2 and strongly antagonizes the biological activity of active mIL-2 mutant proteins that have defects in interactions with the high affinity receptor. Residue 141 mutant proteins bind with reduced affinity to T cells expressing the high affinity IL-2 receptor, yet bind normally to transfected fibroblasts expressing only the alpha and beta chains of the receptor. These results suggest that a third receptor component is important for both binding and signal transduction.
Insights
Mutations in mouse interleukin-2 (mIL-2) at residue 141 impact its biological activity. The Asp141 mutant shows reduced binding and signaling, suggesting a third receptor component is crucial for mIL-2 function.
Area of Science:
- Immunology
- Molecular Biology
- Protein Engineering
Background:
- Mouse interleukin-2 (mIL-2) is a cytokine critical for T cell proliferation and function.
- Specific residues in mIL-2 mediate interactions with its high-affinity receptor complex.
- Previous studies indicate that alterations at residue 141 can affect mIL-2's biological activity.
Purpose of the Study:
- To investigate the functional consequences of substitutions at residue 141 of mIL-2.
- To determine the role of residue 141 in mIL-2 binding and signal transduction.
- To elucidate the contribution of different receptor components to mIL-2 activity.
Main Methods:
- Site-directed mutagenesis was used to create mIL-2 variants with substitutions at residue 141 (e.g., Asp141).
- Biological activity assays were performed to measure the maximal response induced by mutant mIL-2 proteins.
- Binding affinities of mutant proteins to T cells and transfected fibroblasts expressing specific IL-2 receptor subunits were assessed.
Main Results:
- mIL-2 proteins with substitutions at Gln141 exhibited reduced maximal biological responses.
- The Asp141 mutant induced the lowest maximal response and showed antagonistic effects on mIL-2 activity.
- Residue 141 mutant proteins displayed reduced affinity for T cells with the high-affinity IL-2 receptor but normal binding to cells expressing only alpha and beta receptor chains.
Conclusions:
- Residue 141 is critical for mediating the maximal biological response of mIL-2.
- The reduced binding affinity of residue 141 mutants to the high-affinity receptor suggests this site is involved in receptor interaction.
- These findings imply that a third component of the IL-2 receptor complex, beyond the alpha and beta chains, is essential for both high-affinity binding and signal transduction.