Understanding how small molecules / bioactive natural products interact with their biological targets at a quantitative and thermodynamic level is essential for elucidating mechanisms of action and advancing lead compounds. As a company specializing in bioactive natural products target identification, we focus on advanced label-free biophysical technologies that preserve the native state of biomolecules.
Among these technologies, isothermal titration calorimetry (ITC) is widely recognized as a gold-standard method for characterizing biomolecular interactions. ITC provides direct, quantitative, and comprehensive thermodynamic information without the need for labels, reporters, or surface immobilization. Our ITC-based technology platform is designed to support target identification, hit validation, and mechanistic studies for natural products and other bioactive compounds.
What is ITC
ITC is a biophysical technique that measures the heat change associated with molecular interactions in solution. By directly detecting heat released or absorbed during binding events, ITC enables quantitative analysis of interactions between proteins and ligands under near-physiological conditions. Unlike indirect assays that rely on fluorescence, radioactivity, or affinity tags, ITC is entirely label-free and does not require chemical modification of either binding partner. This makes ITC particularly suitable for studying natural products, which often possess complex structures and diverse physicochemical properties. A single ITC experiment provides key binding parameters, including affinity, stoichiometry, and thermodynamic signatures, offering a complete picture of molecular recognition.
Principle of ITC
The fundamental principle of ITC is the direct measurement of heat changes that occur during biomolecular binding processes. When a ligand, such as a bioactive natural compound, interacts with a target protein, the binding event is accompanied by either heat release (exothermic) or heat absorption (endothermic). ITC instruments maintain a constant temperature (isothermal conditions) and detect minute heat differences between a sample cell and a reference cell. These heat differences arise solely from molecular interactions occurring in solution. By continuously monitoring the heat flow required to maintain thermal equilibrium, ITC captures the energetic consequences of binding in real time. Analysis of the heat signal as a function of ligand-to-protein ratio allows determination of key thermodynamic parameters, including the binding constant, stoichiometry, enthalpy change, and entropy change. Together, these parameters provide deep insights into the driving forces and mechanisms underlying molecular interactions.
Fig. 1. The principle of ITC [1].
Our ITC-based Technology Platform
Our ITC-based technology platform has been specifically optimized for natural product target identification and validation. We combine high-sensitivity calorimetric instrumentation with extensive expertise in protein biochemistry, assay design, and natural compound characterization.
The platform supports a broad range of biological targets, including enzymes, receptors, transcription factors, and protein–protein interaction interfaces. Special attention is paid to buffer compatibility, compound solubility, protein stability, and data quality control—factors that are particularly critical when working with chemically diverse natural products. Moreover, by integrating ITC with other label-free approaches, our platform enables robust confirmation of direct target engagement and quantitative comparison of binding properties across compound libraries.
Typical Workflow of ITC
Step 1
Experimental Setup and Temperature Equilibration
The reference and sample cells are equilibrated to the defined experimental temperature under strictly controlled isothermal conditions, with optimized buffer matching to minimize background signals.
Step 2
Protein and Compound Loading
The purified target protein is loaded into the sample cell, while the bioactive natural compound is prepared at an appropriate concentration and loaded into a high-precision injection syringe.
Step 3
Incremental Titration
The natural active compound is injected into the protein solution in multiple, accurately controlled increments, enabling systematic variation of ligand-to-protein molar ratios.
Step 4
Ultra-sensitive Calorimetric Detection
Binding between the compound and the target protein generates minute heat changes, which are detected with sensitivity down to millionths of a degree Celsius.
Step 5
Heat Recording and Equilibrium Monitoring
For each injection, the microcalorimeter records all heat released or absorbed until binding equilibrium is reached, with the measured heat directly proportional to the extent of interaction.
Step 6
Data analysis and Thermodynamic Profiling
Using integrated ITC software, calorimetric data are fitted to appropriate binding models to extract key thermodynamic parameters, including binding affinity, stoichiometry, enthalpy, and entropy.
Step 7
Result Interpretation and Reporting
Thermodynamic results are interpreted in a biological and mechanistic context to support target identification, validation, and downstream drug discovery decisions.
Key Advantages of ITC
- True label-free measurement, preserving native protein and ligand states
- Direct and quantitative detection of binding events without indirect reporters
- Comprehensive thermodynamic profiling in a single experiment
- High physiological relevance, as measurements are performed in solution
- Broad applicability to diverse natural product structures and target classes
- High confidence data, minimizing false positives and assay artifacts
These strengths make ITC an indispensable component of modern natural product–based drug discovery.
ITC is a powerful analytical technique used to determine the thermodynamic parameters of interactions in solution. Our company utilizes ITC to provide an unbiased, high-precision look at these interactions. ITC not only reveals whether a molecule binds, but also uncovers the energetic "story" of the interaction, providing critical thermodynamic evidence that supports the identification and validation of targets for bioactive natural products.
Online Inquiry
Reference
- Jiang X., et al. Recent advances in identifying protein targets of bioactive natural products[J]. Heliyon, 2024, 10(13).
Frequently Asked Questions (FAQ)
Q1: What information can ITC provide beyond binding affinity?
Q2: Is ITC suitable for weak interactions?
A: Yes. With appropriate experimental design, ITC can characterize weak to moderate binding interactions commonly observed in early drug discovery.
Q3: How does ITC support target identification?
A: ITC directly confirms physical binding between a compound and a target protein, providing strong evidence of target engagement.
Q4: Can I use ITC to study the competition between two ligands?
A: Yes, competitive titration is a powerful application of ITC to determine if a new natural product competes for the same binding site as a known inhibitor.