Structural and thermodynamic studies of binding saturated fatty acids to bovine β-lactoglobulin

Lactoglobulin is a globular milk protein for which physiological function has not been clarified. Due to its binding properties lactoglobulin might serve as a carrier for bioactive molecules. Binding of 12-, 14-, 16- and 18-carbon saturated fatty acids to bovine β-lactoglobulin has been characterised by isothermal titration calorimetry and X-ray crystallography as a part of systematic studies of lactoglobulin complexes with ligands of biological importance. The thermodynamic parameters have been determined for lauric, myristic and palmitic acid complexes revealing systematic decrease of enthalpic and increase of entropic component of ΔG with elongation of aliphatic chain. In all crystal structures determined with resolution 1.9-2.1Å, single fatty acid molecule was found in the β-barrel in extended conformation with individual pattern of interactions. Location of a fatty acid in the binding site depends on the length of aliphatic chain and influences polar interactions between protein and ligand. Systematic changes of entropic component indicate important role of water in binding process.