Bound Fatty Acids Modulate the Sensitivity of Bovine β-Lactoglobulin to Chemical and Physical Denaturation

Fatty acids are the natural ligands associated with the bovine milk lipocalin, β-lactoglobulin (BLG), and were identified by means of mass spectrometry. The naturally bound ligands were found to contribute to the stability of the proteins toward denaturation by both temperature and chaotropes. To assess the nature of the structural regions involved in this stabilization, the thermodynamic and kinetic aspects of the stability of various structural regions of the proteins were studied in the presence of bound palmitate, which is the most abundant natural ligand. Binding of a single palmitate molecule was found to affect not only the stability of the calyx region, where palmitate is bound, but also that of the region at the hydrophobic interface between the barrel itself and the long helix in the protein structure, where the thiol group of Cys121 is buried. This region is known to be essential for the stability of the BLG dimer and is relevant to the generation of “reactive monomers” that are involved in covalent and noncovalent polymerization of BLG and in the formation of covalent adducts with other milk proteins.