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Identification of Mediators of T-cell Receptor Signaling via the Screening of Chemical Inhibitor Libraries
Published on: January 22, 2019
An electrostatic selection mechanism controls sequential kinase signaling downstream of the T cell receptor
Neel H Shah1,2,3, Qi Wang1,2,3, Qingrong Yan1,2,3
1Department of Molecular and Cell Biology, University of California, Berkeley, United States.
Abstract:
The sequence of events that initiates T cell signaling is dictated by the specificities and order of activation of the tyrosine kinases that signal downstream of the T cell receptor. Using a platform that combines exhaustive point-mutagenesis of peptide substrates, bacterial surface-display, cell sorting, and deep sequencing, we have defined the specificities of the first two kinases in this pathway, Lck and ZAP-70, for the T cell receptor ζ chain and the scaffold proteins LAT and SLP-76. We find that ZAP-70 selects its substrates by utilizing an electrostatic mechanism that excludes substrates with positively-charged residues and favors LAT and SLP-76 phosphosites that are surrounded by negatively-charged residues. This mechanism prevents ZAP-70 from phosphorylating its own activation loop, thereby enforcing its strict dependence on Lck for activation. The sequence features in ZAP-70, LAT, and SLP-76 that underlie electrostatic selectivity likely contribute to the specific response of T cells to foreign antigens.
Insights
Researchers identified how specific kinases, Lck and ZAP-70, initiate T cell signaling. ZAP-70 uses an electrostatic mechanism to select substrates, ensuring proper T cell activation and response to antigens.
Area of Science:
- Immunology
- Molecular Biology
- Biochemistry
Background:
- T cell activation initiates signaling cascades crucial for adaptive immunity.
- Tyrosine kinases, including Lck and ZAP-70, play pivotal roles in T cell receptor signaling.
- Understanding kinase-substrate specificity is key to deciphering immune responses.
Purpose of the Study:
- To define the substrate specificities of Lck and ZAP-70.
- To elucidate the molecular mechanisms governing early T cell receptor signaling events.
- To investigate how kinase specificity contributes to T cell response.
Main Methods:
- Utilized a platform combining point-mutagenesis, bacterial surface display, cell sorting, and deep sequencing.
- Analyzed the specificities of Lck and ZAP-70 for T cell receptor ζ chain, LAT, and SLP-76.
- Investigated substrate selection mechanisms based on amino acid sequence features.
Main Results:
- Defined the specificities of Lck and ZAP-70 for key T cell signaling components.
- Discovered that ZAP-70 employs an electrostatic mechanism for substrate selection, favoring negatively charged residues.
- Demonstrated that this mechanism prevents autophosphorylation and ensures Lck-dependent activation of ZAP-70.
Conclusions:
- ZAP-70's substrate selection is governed by electrostatic interactions, ensuring precise signaling events.
- This electrostatic selectivity is critical for the ordered activation of T cell signaling pathways.
- The identified sequence features likely contribute to the specificity of T cell responses to foreign antigens.
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