Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda Chiba, 278-8510, Japan.
Artificial Intelligence Research Center, National Institute of Advanced Industrial Science and Technology (AIST), 2-4-7 Aomi, Koto-ku, Tokyo, 135-0064, Japan.
Commun Biol. 2023 Sep 21;6(1):961. doi: 10.1038/s42003-023-05336-6.
Most Gram-negative bacteria synthesize osmo-regulated periplasmic glucans (OPG) in the periplasm or extracellular space. Pathogenicity of many pathogens is lost by knocking out opgG, an OPG-related gene indispensable for OPG synthesis. However, the biochemical functions of OpgG and OpgD, a paralog of OpgG, have not been elucidated. In this study, structural and functional analyses of OpgG and OpgD from Escherichia coli revealed that these proteins are β-1,2-glucanases with remarkably different activity from each other, establishing a new glycoside hydrolase family, GH186. Furthermore, a reaction mechanism with an unprecedentedly long proton transfer pathway among glycoside hydrolase families is proposed for OpgD. The conformation of the region that forms the reaction pathway differs noticeably between OpgG and OpgD, which explains the observed low activity of OpgG. The findings enhance our understanding of OPG biosynthesis and provide insights into functional diversity for this novel enzyme family.
大多数革兰氏阴性菌在周质或细胞外空间合成渗透压调节的周质聚糖（OPG）。敲除与 OPG 合成必不可少的 OPG 相关基因 opgG 会使许多病原体的致病性丧失。然而，OpgG 和 OpgD（OpgG 的旁系同源物）的生化功能尚未阐明。在这项研究中，对大肠杆菌中 OpgG 和 OpgD 的结构和功能分析表明，这些蛋白是β-1,2-葡聚糖酶，彼此之间的活性差异显著，建立了一个新的糖苷水解酶家族 GH186。此外，还提出了 OpgD 具有糖苷水解酶家族中前所未有的长质子转移途径的反应机制。形成反应途径的区域的构象在 OpgG 和 OpgD 之间有明显的差异，这解释了 OpgG 观察到的低活性。这些发现增强了我们对 OPG 生物合成的理解，并为这个新的酶家族的功能多样性提供了深入的认识。
