Using bound fatty acids to disclose the functional structure of serum albumin

Background: Serum albumin is a major transport protein in mammals and is known to have at least seven binding sites for long-chain fatty acids (FAs). Scope of review: We have devised a new electron paramagnetic resonance (EPR) spectroscopic approach to gain information on the functional structure of serum albumin in solution in a coarse-grained manner from the ligands' point of view. Our approach is based on using spin labeled (paramagnetic) stearic acids self-assembled with albumin and subsequent nanoscale distance measurements between the FAs using double electron-electron resonance spectroscopy (DEER). Simple continuous wave (CW) EPR spectroscopy, which allows for quantification of bound ligands, complements our studies. Major conclusions: Based on DEER nanoscale distance measurements, the functional solution structure of human serum albumin (HSA) has remarkably been found to have a much more symmetric distribution of entry points to the FA binding sites than expected from the crystal structure, indicating increased surface flexibility and plasticity for HSA in solution. In contrast, for bovine serum albumin (BSA), the entry point topology is in good agreement with that expected from the crystal structure of HSA. Changes in the solution structures between albumins can hence be revealed and extended to more albumins to detect functional differences at the nanoscale. Going beyond fundamental structural studies, our research platform is also excellently suited for general studies of protein-solvent interactions, temperature effects and ligand binding. General significance: We discuss how our research platform helps illuminate protein dynamics and function and can be used to characterize albumin-based hybrid materials. This article is part of a Special Issue entitled Serum Albumin. (C) 2013 Elsevier B.V. All rights reserved.