Effect of conformational states on protein dynamical transition

タンパク質の動力学転移に対する構造状態の影響

中川 洋   ; 上久保 裕生*; 片岡 幹雄

Nakagawa, Hiroshi; Kamikubo, Hironari*; Kataoka, Mikio

折れ畳まったタンパク質の特性を調べるため、野生型と欠損変異体のスタフィロコッカルヌクレアーゼを用いて非干渉性中性子弾性散乱によりタンパク質の動力学転移に対する構造状態の効果を調べた。変異体はC末端の13残基を欠損させたもので、コンパクトな変性構造を取り、天然変性タンパク質のモデルとされている。非干渉性中性子弾性散乱実験はILLのIN10とIN13で行われた。弾性散乱強度のQ依存性をさまざまな温度で測定し、平均二乗変位を求めた。乾燥タンパク質と水和タンパク質で測定を行った。水和タンパク質では野生型と変異体では差がなかったが、乾燥状態では差が見られた。140Kの転移は乾燥状態と水和状態の両方で見られるが、転移温度前後での平均二乗変位の温度依存性は両者で異なり、折り畳みによる構造のハードニングが見られた。水和によってさらに240Kの転移が生じるが、構造状態には依存しない。これにより水和水のダイナミクスがタンパク質動力学を支配していると言える。

In order to examine the properties specific to the folded protein, the effect of the conformational states on protein dynamical transition was studied by incoherent elastic neutron scattering for both wild type and a deletion mutant of staphylococcal nuclease. The deletion mutant of SNase which lacks C-terminal 13 residues takes a compact denatured structure, and can regard as a model of intrinsic unstructured protein. Incoherent elastic neutron scattering experiments were carried out at various temperature between 10K and 300K on IN10 and IN13 installed at ILL. Temperature dependence of mean square displacements was obtained by the q-dependence of elastic scattering intensity. The measurements were performed on dried and hydrated powder samples. No significant differences were observed between wild type and the mutant for the hydrated samples, while significant differences were observed for the dried samples. A dynamical transition at 140K observed for both dried and hydrated samples. The slopes of the temperature dependence of MSD before transition and after transition are different between wild type and the mutant, indicating the folding induces hardening. The hydration water activates a further transition at 240K. The behavior of the temperature dependence of MSD is indistinguishable for wild type and the mutant, indicating that hydration water dynamics dominate the dynamical properties.