Takagi Emiko, Hatada Yuji, Akita Masatake, Ohta Yukari, Yokoi Gaku, Miyazaki Takatsugu, Nishikawa Atsushi, Tonozuka Takashi
a Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , Yokosuka , Japan.
Biosci Biotechnol Biochem. 2015;79(4):625-32. doi: 10.1080/09168451.2014.988680. Epub 2014 Dec 6.
A deep-sea bacterium, Microbulbifer thermotolerans JAMB-A94, has a β-agarase (MtAgaA) belonging to the glycoside hydrolase family (GH) 16. The optimal temperature of this bacterium for growth is 43-49 °C, and MtAgaA is stable at 60 °C, which is one of the most thermostable enzymes among GH16 β-agarases. Here, we determined the catalytic domain structure of MtAgaA. MtAgaA consists of a β-jelly roll fold, as observed in other GH16 enzymes. The structure of MtAgaA was most similar to two β-agarases from Zobellia galactanivorans, ZgAgaA, and ZgAgaB. Although the catalytic cleft structure of MtAgaA was similar to ZgAgaA and ZgAgaB, residues at subsite -4 of MtAgaA were not conserved between them. Also, an α-helix, designated as α4', was uniquely located near the catalytic cleft of MtAgaA. A comparison of the structures of the three enzymes suggested that multiple factors, including increased numbers of arginine and proline residues, could contribute to the thermostability of MtAgaA.
一种深海细菌，嗜热微小杆菌JAMB-A94，拥有一种属于糖苷水解酶家族（GH）16的β-琼脂酶（MtAgaA）。这种细菌生长的最适温度为43-49°C，且MtAgaA在60°C时稳定，这使其成为GH16β-琼脂酶中最耐热的酶之一。在此，我们确定了MtAgaA的催化结构域结构。MtAgaA由β-果冻卷折叠组成，这与其他GH16酶中观察到的结构相同。MtAgaA的结构与来自食半乳聚糖海杆菌的两种β-琼脂酶ZgAgaA和ZgAgaB最为相似。尽管MtAgaA的催化裂隙结构与ZgAgaA和ZgAgaB相似，但MtAgaA在亚位点-4处的残基在它们之间并不保守。此外，一个被命名为α4'的α-螺旋独特地位于MtAgaA催化裂隙附近。对这三种酶结构的比较表明，包括精氨酸和脯氨酸残基数量增加在内的多种因素可能有助于MtAgaA的热稳定性。
