Aunkham Anuwat, Zahn Michael, Kesireddy Anusha, Pothula Karunakar Reddy, Schulte Albert, Baslé Arnaud, Kleinekathöfer Ulrich, Suginta Wipa, van den Berg Bert
Biochemistry-Electrochemistry Research Unit, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima, 30000, Thailand.
Institute for Cell and Molecular Biosciences, The Medical School, Newcastle University, Newcastle upon Tyne, NE2 4HH, UK.
Nat Commun. 2018 Jan 15;9(1):220. doi: 10.1038/s41467-017-02523-y.
Chitin, an insoluble polymer of N-acetylglucosamine, is one of the most abundant biopolymers on Earth. By degrading chitin, chitinolytic bacteria such as Vibrio harveyi are critical for chitin recycling and maintenance of carbon and nitrogen cycles in the world's oceans. A decisive step in chitin degradation is the uptake of chito-oligosaccharides by an outer membrane protein channel named chitoporin (ChiP). Here, we report X-ray crystal structures of ChiP from V. harveyi in the presence and absence of chito-oligosaccharides. Structures without bound sugar reveal a trimeric assembly with an unprecedented closing of the transport pore by the N-terminus of a neighboring subunit. Substrate binding ejects the pore plug to open the transport channel. Together with molecular dynamics simulations, electrophysiology and in vitro transport assays our data provide an explanation for the exceptional affinity of ChiP for chito-oligosaccharides and point to an important role of the N-terminal gate in substrate transport.
几丁质是一种由N-乙酰葡糖胺组成的不溶性聚合物，是地球上最丰富的生物聚合物之一。通过降解几丁质，诸如哈维氏弧菌等几丁质分解细菌对于几丁质循环利用以及世界海洋中碳和氮循环的维持至关重要。几丁质降解的一个决定性步骤是一种名为几丁质孔蛋白（ChiP）的外膜蛋白通道对壳寡糖的摄取。在此，我们报告了哈维氏弧菌的ChiP在存在和不存在壳寡糖情况下的X射线晶体结构。没有结合糖的结构揭示了一种三聚体组装，相邻亚基的N端使转运孔出现前所未有的关闭。底物结合会排出孔塞以打开转运通道。结合分子动力学模拟、电生理学和体外转运测定，我们的数据解释了ChiP对壳寡糖的特殊亲和力，并指出N端门控在底物转运中的重要作用。
