Fatty Acid Binding to Human Serum Albumin in Blood Serum Characterized by EPR Spectroscopy

One of the functions of Human Serum Albumin (HSA) is binding and transport of fatty acids. This ability could be altered by the presence of several blood components such as toxins or peptides – which in turn alters the functionality of the protein. We aim at characterizing HSA and its fatty acid binding in native serum environment. Native ligand binding and deviations from normal function can be monitored by electron paramagnetic resonance (EPR) spectroscopy using spin labeled fatty acids (FAs). Blood serum from healthy individuals is used to examine healthy HSA in its natural physiological conditions at different loading ratios of protein to FAs. Among the EPR spectroscopic parameters (like hyperfine coupling, line shape, rotational correlation time and population of different binding sites) the rotational correlation time is found to differ significantly between binding sites of the protein, especially at loading ratios of four FAs per HSA. Although differences are observed between individual samples, a general trend regarding the dynamics of healthy HSA at different loading ratios could be obtained and compared to a reference of purified commercially available HSA in buffer.