THz spectroscopy and molecular modeling of bovine serum albumin under various hydration conditions

Bovine serum albumin (BSA) is the most abundant protein in bovine plasma; its three dimensional structure is yet unknown. We investigated the structure and dynamics of BSA in lyophilized samples, in 10% w/w and 50% w/w BSA aqueous solutions using THz spectroscopy and molecular modeling. THz spectra were recorded with a spectral resolution of 7.4 GHz. Theoretical spectra were simulated using a structural model of BSA based on the homology with the known structure of human serum albumin (HSA). The agreement between simulated THz spectra and THz spectra recorded experimentally allowed us to validate the BSA model and the solution models. Based on these models we investigated the flexibility of dry BSA and of BSA with one hydration layer. The hydrated structure of BSA is less flexible than the structure free of water molecules, except for residues 54 - 104 that are more mobile in the hydrated structure. We also investigated the fluctuations of the water molecules within the first hydration layer and identified two groups of water molecules: one that exhibits small fluctuations and one of highly mobile water molecules. These molecules are associated to highly mobile regions from the proteins and move in positive correlation with the neighboring protein regions. We also propose a BSA dimerization model in which the molecules strongly interact. The fluctuations of the BSA monomers and of their first hydration layer were investigated. The two molecules display similar fluctuation patterns, but one of them is slightly more flexible.