Role of solvent on protein-matrix coupling in MbCO embedded in water-saccharide systems: a Fourier transform infrared spectroscopy study.

Embedding protein in sugar systems of low water content enables one to investigate the protein dynamic-structure function in matrixes whose rigidity is modulated by varying the content of residual water. Accordingly, studying the dynamics and structure thermal evolution of a protein in sugar systems of different hydration constitutes a tool for disentangling solvent rigidity from temperature effects. Furthermore, studies performed using different sugars may give information on how the detailed composition of the surrounding solvent affects the internal protein dynamics and structural evolution. In this work, we compare Fourier transform infrared spectroscopy measurements (300-20 K) on MbCO embedded in trehalose, sucrose, maltose, raffinose, and glucose matrixes of different water content. At all the water contents investigated, the protein-solvent coupling was tighter in trehalose than in the other sugars, thus suggesting a molecular basis for the trehalose peculiarity. These results are in line with the observation that protein-matrix phase separation takes place in lysozyme-lactose, whereas it is absent in lysozyme-trehalose systems; indeed, these behaviors may respectively be due to the lack or presence of suitable water-mediated hydrogen-bond networks, which match the protein surface to the surroundings. The above processes might be at the basis of pattern recognition in crowded living systems; indeed, hydration shells structural and dynamic matching is first needed for successful come together of interacting biomolecules.