Bagautdinov Bagautdin, Matsuura Yoshinori, Yamamoto Hitoshi, Sawano Masahide, Ogasahara Kyoko, Takehira Michiyo, Kunishima Naoki, Katoh Etsuko, Yutani Katsuhide
RIKEN SPring-8 Center, RIKEN, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan; Institute for Protein Research, Osaka University, 3-2 Yamada-oka, Suita, Osaka 565-0871, Japan; and National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-0856, Japan.
RIKEN SPring-8 Center, RIKEN, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan; Institute for Protein Research, Osaka University, 3-2 Yamada-oka, Suita, Osaka 565-0871, Japan; and National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-0856, Japan
J Biochem. 2015 Mar;157(3):169-76. doi: 10.1093/jb/mvu062. Epub 2014 Oct 24.
Unusually stable proteins are a disadvantage for the metabolic turnover of proteins in cells. The CutA1 proteins from Pyrococcus horikoshii and from Oryza sativa (OsCutA1) have unusually high denaturation temperatures (Td) of nearly 150 and 100 °C, respectively, at pH 7.0. It seemed that the CutA1 protein from the human brain (HsCutA1) also has a remarkably high stability. Therefore, the thermodynamic stabilities of HsCutA1 and its protease susceptibility were examined. The Td was remarkably high, being over 95 °C at pH 7.0. The unfolding Gibbs energy (ΔG(0)H2O) was 174 kJ/mol at 37 °C from the denaturant denaturation. The thermodynamic analysis showed that the unfolding enthalpy and entropy values of HsCutA1 were considerably lower than those of OsCutA1 with a similar stability to HsCutA1, which should be related to flexibility of the unstructured properties in both N- and C-terminals of HsCutA1. HsCutA1 was almost completely digested after 1-day incubation at 37 °C by subtilisin, although OsCutA1 was hardly digested at the same conditions. These results indicate that easily available fragmentation of HsCutA1 with remarkably high thermodynamic stability at the body temperature should be important for its protein catabolism in the human cells.
异常稳定的蛋白质对细胞内蛋白质的代谢周转不利。来自嗜热栖热菌和水稻的CutA1蛋白（OsCutA1）在pH 7.0时具有异常高的变性温度（Td），分别接近150和100°C。人脑中的CutA1蛋白（HsCutA1）似乎也具有非常高的稳定性。因此，研究了HsCutA1的热力学稳定性及其对蛋白酶的敏感性。其Td非常高，在pH 7.0时超过95°C。根据变性剂变性结果，在37°C时其展开吉布斯自由能（ΔG(0)H2O）为174 kJ/mol。热力学分析表明，HsCutA1的展开焓和熵值明显低于具有与HsCutA1相似稳定性的OsCutA1，这应该与HsCutA1 N端和C端非结构化特性的灵活性有关。尽管在相同条件下OsCutA1几乎不被消化，但HsCutA1在37°C下用枯草杆菌蛋白酶孵育1天后几乎被完全消化。这些结果表明，HsCutA1在体温下具有非常高的热力学稳定性且易于碎片化，这对其在人体细胞中的蛋白质分解代谢应该很重要。
