Utilizing Thermal Shift Assay to Probe Substrate Binding to Selenoprotein O
August 9th, 2024
Here, we present the thermal shift assay, a high-throughput, fluorescence-based technique used to investigate the binding of small molecules to proteins of interest.
We aim to study the biochemical activity of proteins with unknown functions. Cofactor binding is not only essential for the activity of some proteins, but may also alter their thermal stability. One practical application of this phenomenon lies in utilizing the change in thermal stability, as measured by the protein's melting temperature, to analyze ligand binding.
Thermal shift assay is a versatile tool for investigating protein interactions with potential cofactors or drugs and for identifying stabilizing conditions for crystallography. Some of its advantages over other screening methods are its relatively simple setup and high throughput with 96 or 384 well plates. Selenoprotein O, or SelO, is an evolutionarily conserved pseudokinase that transfers adenosine monophosphate from ATP to protein substrates in a post-translational modification known as AMPylation In this protocol, we use TSA to analyze nucleotide and metal binding to SelO.
To begin, prepare SelO protein solution using thermal shift assay or TSA buffer. Dispense the protein, small molecules, and SYPRO Orange dye to the appropriate wells of a 384 well plate. Cover the plate with optically clear adhesive film, and briefly spin down the plate at 1000g for one minute in a centrifuge.
Then place the plate in a real-time PCR machine and program it to hold the sample at 20 degrees Celsius for two minutes followed by a 0.5 degree increase in temperature per minute up to 95 degrees Celsius. Export the data from the RTPCR machine for relative fluorescence units, or RFU, with respect to temperature. Using the software of choice, extract and plot data points up to the highest intensity measured for each melting curve.
Determine the melting temperature with the Boltzmann sigmoidal fit for the data to determine the melting temperature, or Tm.The thermal denaturation curves indicated a 4 degrees Celsius increase in the thermal stability of Escherichia coli SelO in the presence of ATP with magnesium ions and a 12 degrees Celsius rise in the same for ATP with manganese ions. However, there was no shift in thermal stability upon incubation with UTP, indicating that Escherichia coli SelO may not exhibit detectable binding to UTP. The no protein as well as the no dye controls had low fluorescence signal which was not responsive to the temperature increase.
Overview
This article presents the thermal shift assay (TSA), a high-throughput, fluorescence-based technique for investigating the binding of small molecules to proteins. The TSA is particularly useful for analyzing ligand binding and determining stabilizing conditions for crystallography.
Key Study Components
Area of Science
- Biochemistry
- Protein interactions
- Thermal stability analysis
Background
- Cofactor binding is essential for the activity of some proteins.
- Changes in thermal stability can indicate ligand binding.
- The melting temperature of proteins is a key measurement in TSA.
- Selenoprotein O (SelO) is a pseudokinase involved in AMPylation.
Purpose of Study
- To study the biochemical activity of proteins with unknown functions.
- To utilize TSA for analyzing nucleotide and metal binding to SelO.
- To identify stabilizing conditions for protein crystallography.
Methods Used
- Thermal shift assay (TSA)
- Fluorescence-based detection
- High-throughput screening with 96 or 384 well plates
- Analysis of ligand binding through thermal stability changes
Main Results
- TSA effectively measures ligand binding to proteins.
- SelO's interactions with nucleotides and metals were analyzed.
- Thermal stability changes were correlated with ligand binding.
- The method demonstrated advantages over traditional screening techniques.
Conclusions
- The thermal shift assay is a versatile tool for protein interaction studies.
- It provides insights into the biochemical activity of proteins.
- TSA can facilitate the identification of stabilizing conditions for crystallography.
Frequently Asked Questions
Executive Industry Relevance
Thermal shift assay (TSA) enables rapid, high-throughput assessment of ligand binding and protein stability, directly supporting early-stage target validation and mechanistic de-risking in biopharma discovery. By quantifying substrate and cofactor interactions with Selenoprotein O, TSA informs both functional annotation and the identification of stabilizing conditions for downstream structural studies. This approach enhances predictive confidence at critical inflection points in the discovery pipeline, particularly for proteins with previously unknown functions.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables direct interrogation of ligand and cofactor binding to uncharacterized proteins.
- Supports mechanistic de-risking by revealing substrate specificity and binding dependencies.
- Facilitates functional target validation through quantitative thermal stability shifts.
- Provides actionable data for portfolio triage of novel protein targets.
Screening & Assay Development
- Delivers high-throughput, plate-based screening of multiple ligand conditions.
- Standardizes assay outputs via quantitative melting temperature measurements.
- Enables reproducible evaluation of protein-ligand interactions for assay readiness.
- Supports identification of optimal conditions for structural and functional studies.
Translational & Preclinical Research
- Aligns biochemical findings with disease-relevant protein function when substrate specificity is established.
- Provides continuity from discovery to preclinical validation for novel targets.
- Reduces risk of late-stage failure by clarifying molecular mechanisms early.
Pipeline & Workflow Integration
TSA is positioned at the interface of early discovery and lead identification, enabling hypothesis-driven target validation and supporting downstream assay development and structural biology workflows.
- Discovery Biology: Quantifies ligand binding and cofactor requirements to clarify protein function.
- Screening: Provides scalable, reproducible outputs for compound and condition evaluation.
- Analytics: Generates melting temperature data for comparative analysis across experimental conditions.
- Translational Research: Bridges biochemical characterization with preclinical model selection when relevant.
- Enterprise Reuse: Offers a broadly applicable platform for diverse protein targets and ligand classes.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence and reduces mechanistic ambiguity in target selection.
- Operational Value: Streamlines assay setup, enhances reproducibility, and supports high-throughput workflows.
- Strategic Value: Improves go/no-go decision-making and capital allocation by clarifying target-ligand relationships.
- Portfolio Impact: Enables risk-adjusted prioritization of novel targets based on quantitative binding data.
Implementation Considerations
- Requires expertise in protein biochemistry and fluorescence-based assay design.
- Needs access to real-time PCR or compatible thermal cyclers and plate readers.
- Demands standardized protocols for cross-team reproducibility and data comparability.
- May require adaptation for different protein classes or ligand types.
- Dependent on protein purity and stability for reliable measurements.
