Finke John M, Jennings Patricia A
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla 92093-0359, USA.
Biochemistry. 2002 Dec 17;41(50):15056-67. doi: 10.1021/bi026197k.
The thermodynamic stability and folding kinetics of the all beta-sheet protein interleukin-1beta were measured between 0 and 4 M GdmCl concentrations and pH 5-7. Native interleukin-1beta undergoes a 3.5 kcal/mol decrease in thermodynamic stability, Delta, as pH is increased from 5 to 7. The native state parameter m(NU), measuring protein destabilization/[GdmCl], remains constant between pH 5 and 7, indicating that the solvent-exposed surface area difference between the native state and unfolded ensemble is unchanged across this pH range. Similarly, pH changes between 5 and 7 decrease only the thermodynamic stability, DeltaG(H)2(O), and not the m-values, of the kinetic intermediate and transition states. This finding is shown to be consistent with transition state configurations which continue to be the high-energy configurations of the transition state in the face of changing stability conditions. A three-state folding mechanism U right arrow over left arrow I right arrow over left arrow N is shown to be sufficient in characterizing IL-1beta folding under all conditions studied. The m-values of refolding transitions are much larger than the m-values of unfolding transitions, indicating that that the fast, T(2) (U right arrow over left arrow I), and slow, T(1) (I right arrow over left arrow N), transition states are highly similar to the intermediate I and native state N, respectively. Many of the folding properties of interleukin-1beta are shared among other members of the beta-trefoil protein family, although clear differences can exist.
在0至4 M盐酸胍（GdmCl）浓度以及pH值为5至7的条件下，对全β折叠蛋白白细胞介素-1β（interleukin-1β）的热力学稳定性和折叠动力学进行了测定。随着pH值从5增加到7，天然态白细胞介素-1β的热力学稳定性降低了3.5千卡/摩尔（Δ）。测量蛋白质去稳定化程度与[GdmCl]关系的天然态参数m(NU)在pH值5至7之间保持恒定，这表明在该pH范围内，天然态与未折叠态集合之间溶剂暴露表面积的差异没有变化。同样，pH值在5至7之间的变化仅降低了动力学中间体和过渡态的热力学稳定性ΔG(H)2(O)，而没有改变m值。这一发现与过渡态构型一致，即在稳定性条件变化时，过渡态构型仍然是高能构型。在所有研究条件下，三态折叠机制U⇄I⇄N足以描述白细胞介素-1β的折叠过程。复性转变的m值远大于变性转变的m值，这表明快速转变T(2)（U⇄I）和慢速转变T(1)（I⇄N）的过渡态分别与中间体I和天然态N高度相似。白细胞介素-1β的许多折叠特性在β三叶蛋白家族的其他成员中也有共同之处，尽管可能存在明显差异。
