Since the late 70s, MicroCal (part of GE Healthcare) has been dedicated to developing sensitive, easy-to-use microcalorimeters. Because of our long history of passionate innovation, microcalorimetry is among the fastest growing areas of life science research.
GE Healthcare’s MicroCal systems allow characterization of biomolecular interactions by providing direct, label-free measurements of binding affinity and thermodynamics.
Microcalorimetry studies provide valuable information about binding interactions, molecular stability, protein folding, and enzyme kinetics. Read more below or go to the Microcalorimetry section to learn about isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC).
MicroCal systems are used in a wide range of areas from basic research to the discovery and development of small molecules, biotherapeutics, and vaccines. Our customers include pharmaceutical, biotech, academic, and governmental institutions worldwide.
Binding Studies with Isothermal Titration Calorimetry (ITC)
All cellular processes require specific binding and molecular recognition between biomolecules. Knowledge of these interactions is critical to understanding how proteins, nucleic acids and lipids and other biomolecules function in biological systems. Even with rapid advances in structural biology, knowledge of structure alone does not ensure accurate prediction of function and biological activity. The complete characterization of any binding interaction requires knowledge of the affinity, number of binding sites, and the thermodynamics.
In a single ITC experiment, you can determine binding affinity (KD), stoichiometry or number of binding sites, enthalpy (ΔH), and entropy (ΔS). Thermodynamic data, specifically ΔH and ΔS, reveal the forces that drive complex formation and mechanism of action. Thermodynamic measurements provide information on conformational changes, hydrogen bonding, hydrophobic interactions, and charge-charge interactions. This information can be used to describe the function and mechanism at a molecular level.
- The Advantages of MicroCal Auto-iTC200 for secondary screening in a fragment-based drug discovery campaign
- Revealing kinase inhibitor mechanisms: ITC leads the way
- Divided we fall? Studying low-affinity fragments of ligands by ITC
Assessing Stability with Differential Scanning Calorimetry (DSC)
Biological macromolecules like protein, lipids, and nucleic acids are stabilized by noncovalent intramolecular interactions. Intermolecular non-covalent interactions stabilize any complexes formed between biomolecules. All biological processes depend on macromolecules being stable and in the appropriate folded conformation. It is important to know how proteins fold into their biologically active states and how these active states are stabilized. A primary goal of protein engineering, rational drug design and biopharmaceutical production is the development, production, and storage of stable proteins with full functionality.
A biomolecule in aqueous solution is in equilibrium between the native (folded) conformation and its denatured (unfolded) conformation. The stability of the native state is based on the magnitude of the Gibbs free energy (∆G) of the system and the thermodynamic relationships between enthalpy (∆H) and entropy (∆S) changes. A positive ∆G indicates the native state is more stable than the denatured state – the more positive the ∆G, the greater the stability. For a protein to unfold, stabilizing forces need to be broken. Conformational entropy overcomes stabilizing forces allowing the protein to unfold at temperatures where entropy becomes dominant. DSC measures ∆H of unfolding due to heat denaturation. The transition midpoint (Tm) is the temperature where 50% of the protein is in its native conformation and the other 50% is denatured. The higher the Tm, the more stable the molecule.
- Preformulation and stability studies of biotherapeutics using DSC
- Better guidance in antibody therapeutics process development using differential scanning calorimetry
- Using DSC to understand the correlation between thermal stability and protein stability
Enzyme catalytic reactions are central to all biological pathways. A major portion of biochemical research is devoted to characterizing enzyme function, activity and structure, and how enzymes are inhibited and activated. Enzyme characterization is also key to drug discovery research since many drug targets are enzymes.
Isothermal Titration Calorimetry (ITC) is well-established in the study of affinity of molecular interactions, and is now becoming a popular tool in the study of enzyme kinetics. The strength of the technique lies in the universal nature of ITC. Traditional enzyme assays utilize a probe to monitor either substrate depletion or product formation. These probes are system-dependent and must be optimized for each reaction under specific conditions. Also, the substrate may need to be modified which could interfere with the catalysis reaction. For optical methods, the experimental conditions can affect the detection system, preventing accurate measurements. This means that with traditional assay methods, many enzymes do not have practical assays.
ITC uses heat as a probe, and since every reaction generates or absorbs heat, there is no need for lengthy method development each time a new enzyme is assayed. ITC directly measures the heat change as catalysis proceeds, which is proportional to the rate of reaction. Todd and Gomez (2001) showed that Km and kcat from ITC experiments agreed favorably with traditional enzyme kinetics methods, and can be used with every class of enzyme, including those with no other direct assay methods.
The use of ITC to monitor the rate of enzymatic reactions is a non-destructive, sensitive, and direct assay. Multiple injections of substrate can be done in a single experiment, so Km and kcat can be determined in a single ITC experiment. With ITC, it is straightforward to vary experimental conditions such as pH and ionic strength, and one can get a complete analysis of catalysis and kinetics. ITC also provides valuable insights on the thermodynamics of enzymatic reactions.