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Updated: May 10, 2026
Peptide-based Identification of Functional Motifs and their Binding Partners
Published on: June 30, 2013
An Intracellular Peptide Library Screening Platform Identifies Irreversible Covalent Transcription Factor Inhibitors
Andrew Brennan1, Scott Lovell1, Keith W Vance1
1Department of Life Sciences, University of Bath, Bath, BA2 7AY, UK.
Abstract:
The development of an intracellular peptide library screening platform is described to identify covalent transcription factor (TF) antagonists. The Transcription Block Survival (TBS) assay and subsequent hit refinement previously produced potent but reversible antagonists of the oncogenic TF cJun. TBS moves beyond a target binding readout to ensure loss of TF function by blocking TF-DNA binding. Here, the TBS methodology is significantly expanded to identify covalent and highly selective inhibitors. A 131,072-member library is probed containing a Cys option at nine positions within a non-reducing cell line. This identified a single Cys residue with the appropriate geometry for disulphide bond formation with cJun C269 in its DNA binding domain. The selection of a unique Cys in the antagonist indicates both target shutdown and concomitant disulphide formation in a single step, resulting in increased potency. Substituting Cys with an electrophile generates an irreversible yet highly selective covalent cJun inhibitor capable of penetrating human melanoma cells in culture and depleting oncogenic cJun levels to inhibit cell viability, with enhanced efficacy compared to a previous cJun-targeting peptide. This enhanced covalent-TBS screening pipeline provides a robust approach to profile target protein surfaces for ligandable cysteines, producing covalent and selective antagonists with appropriately positioned warheads.
Insights
Researchers developed a new screening platform to find covalent inhibitors of transcription factors (TFs). This method identified a potent peptide that irreversibly blocks the oncogenic TF cJun, inhibiting cancer cell viability.
Area of Science:
- Molecular Biology
- Drug Discovery
- Chemical Biology
Background:
- The Transcription Block Survival (TBS) assay was previously used to find reversible antagonists of the transcription factor (TF) cJun.
- Existing methods lack the ability to identify covalent inhibitors and ensure high selectivity.
Purpose of the Study:
- To expand the TBS methodology for identifying covalent and highly selective TF inhibitors.
- To develop a peptide inhibitor targeting the oncogenic TF cJun with enhanced efficacy.
Main Methods:
- Screening of a 131,072-member peptide library with cysteine options for disulfide bond formation.
- Utilizing a non-reducing cell line to identify specific cysteine residues for covalent modification.
- Substituting cysteine with an electrophile to create irreversible covalent inhibitors.
Main Results:
- A single cysteine residue was identified for disulfide bond formation with cJun C269, leading to increased potency.
- A selective covalent cJun inhibitor was generated, capable of penetrating melanoma cells and reducing oncogenic cJun levels.
- The novel inhibitor demonstrated enhanced efficacy compared to previous cJun-targeting peptides.
Conclusions:
- The enhanced covalent-TBS screening pipeline is a robust method for identifying ligandable cysteines on protein surfaces.
- This approach yields potent, selective covalent antagonists with precisely positioned reactive groups.
- The developed inhibitor effectively targets oncogenic cJun, inhibiting cell viability in melanoma models.
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