Analysis of the protein hydration structure in sugar solution by quantum beam

Ajito, Satoshi

no journal, , 

Sugar is a typical bioprotectant, and is known to stabilize structures of protein. Several hypotheses have been proposed even in a simply aqueous solution system. The "hydrogen bond replacement theory" claims that protein structures are stabilized by direct hydrogen bond formation between sugar and protein. On the other hand, The "preferential hydration theory" is claims that the preferential hydration of a protein in a sugar solution put a structural change with denaturation at energetically unfavorabl. In order to structurally prove the above hypothesis, small-angle neutron scattering method and small-angle X-ray scattering method were used complementarily to analyze the hydration structure of the protein in the sugar solution. The small angle scattering method is an effective for structural analysis of biopolymers and synthetic polymers. The small-angle neutron scattering method can control the scattering density of the sample by deuteration, and is effective for multicomponent systems. In this study, the sugar was made invisible and the hydration structure of the protein was selectively observed. Analysis of the protein hydration shell using the neutron small angle scattering method revealed that the hydration shell consisting of only water was retained in the sugar solution, strongly supporting the "selective hydration theory". The result was obtained. Furthermore, as a result of investigating the dependence of "preferential hydration" on the type of sugar using X-ray, while "preferential hydration" was maintained up to about 30% for the disaccharides. For monosaccharides, penetration into the protein hydration shell was observed from around 15%. The results qualitatively explain the superior bioprotective action of disaccharides, and quantification of the above correlation is a future subject.