Functional Application Areas

Protein-Lipid Interactions

Protein-lipid interactions are involved in many biological processes, such as:

  • Formation of cell membranes
  • Cell transport
  • LDL and HDL binding to cholesterol
  • Peptide antibiotics interfering with bacterial phospholipids bilayers
  • Receptor proteins
  • Fatty acid binding proteins involved in cell development, metabolism, and other processes
  • Infection by viruses
  • Formation of amyloids and protein aggregates

Knowledge of these interactions is important to understand how proteins and lipids function in biological systems. There have been rapid advances in structural biology and relating structure to biochemical function and mechanism. However, knowledge of protein and lipid structure alone does not ensure accurate prediction of function and biological activity. The complete characterization of any binding interaction requires a quantification of the affinity, number of binding sites, and the thermodynamics. 

Isothermal Titration Calorimetry (ITC) is vital in the study of multi-probe structure activity relationships (SAR) since it can detect contributions that affinity-only methods may miss.  For example, the affinity measured by these methods may be similar for a wild-type and mutant protein binding to a lipid but ITC can reveal differences in ΔH and ΔS that can describe the mechanism of action of binding.  This information can validate in-silico modeling. ITC is also commonly used to validate other binding assays.

ITC is also used to characterize ligand specificity (i.e. a series of lipids binding a protein), binding of inhibitors of protein-lipid interactions, and allosteric effects of ligands to the protein-lipid interactions.

Since ITC is done in-solution, it can utilize any biological buffer, including detergent to solubilize the lipid.  For a full characterization of a biomolecular interaction, it is important to observe how salt, pH, temperature, etc affects binding affinity and thermodynamics.

Some antibiotics and other drugs interfere with protein-lipid interactions. ITC is also becoming an important tool in characterizing drug-target interactions, and can be used in many different stages of Drug Discovery and Development.

References

The microcalorimetry of lipid membranes
Heerklotz H.
J. Phys.: Condens. Matter 16 R441-R467 (2004)  

ITC – Protein-Lipid Interactions Reference List

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