中国农业科学院杨青和中国科学院高能物理研究所龚勇等研究人员合作揭示定向几丁质生物合成的结构基础。相关论文于2022年9月21日在线发表在《自然》杂志上。

研究人员报告了来自毁灭性的大豆根腐病致病卵菌大豆疫霉（Phytophthora sojae，PsChs1）几丁质合成酶的五个冷冻电镜结构。它们代表了该酶的apo、N-乙酰葡糖胺（GlcNAc）结合、新生几丁质低聚物结合、UDP结合（合成后）和几丁质合成酶抑制剂nikkomycin Z结合的状态，并提供了关于几丁质生物合成的多个步骤及其竞争性抑制的详细观点。这些结构揭示了几丁质合成反应室，其中有底物结合位点、催化中心和聚合物转移通道的入口，该通道允许产品聚合物排出。这种安排反映了几丁质生物合成中从UDP-GlcNAc结合和聚合物延伸到释放产品的连续关键事件。

研究人员在几丁质-易位通道内发现了一个摆动环，它作为一个"门锁"，防止底物离开，同时引导产物聚合物进入易位通道，排放到细胞膜外侧。这项工作揭示了几丁质生物合成的定向多步骤机制，并为抑制几丁质的合成提供了结构基础。

据了解，几丁质是自然界中最丰富的氨基多糖，是一种由GlcNAc单元组成的细胞外聚合物。几丁质生物合成的关键反应由几丁质合成酶催化，它是一种膜整合的糖基转移酶，将GlcNAc从UDP-GlcNAc转移到生长中的几丁质链上。然而，这一过程的精确机制还没有被阐明。

附：英文原文

Title: Structural basis for directional chitin biosynthesis

Author: Wei Chen  Peng Cao  Yuansheng Liu  Ailing Yu2  Dong Wang  Lei Chen  Rajamanikandan Sundarraj  Zhiguang Yuchi  Yong Gong  Hans Merzendorfer &Qing Yang

Issue&Volume: 2022-09-28

Abstract: Chitin, the most abundant aminopolysaccharide in nature, is an extracellular polymer consisting of N-acetylglucosamine (GlcNAc) units1. The key reactions of chitin biosynthesis are catalysed by chitin synthase2,3,4, a membrane-integrated glycosyltransferase that transfers GlcNAc from UDP-GlcNAc to a growing chitin chain. However, the precise mechanism of this process has yet to be elucidated. Here we report five cryo-electron microscopy structures of a chitin synthase from the devastating soybean root rot pathogenic oomycete Phytophthora sojae (PsChs1). They represent the apo, GlcNAc-bound, nascent chitin oligomer-bound, UDP-bound (post-synthesis) and chitin synthase inhibitor nikkomycin Z-bound states of the enzyme, providing detailed views into the multiple steps of chitin biosynthesis and its competitive inhibition. The structures reveal the chitin synthesis reaction chamber that has the substrate-binding site, the catalytic centre and the entrance to the polymer-translocating channel that allows the product polymer to be discharged. This arrangement reflects consecutive key events in chitin biosynthesis from UDP-GlcNAc binding and polymer elongation to the release of the product. We identified a swinging loop within the chitin-translocating channel, which acts as a ‘gate lock’ that prevents the substrate from leaving while directing the product polymer into the translocating channel for discharge to the extracellular side of the cell membrane. This work reveals the directional multistep mechanism of chitin biosynthesis and provides a structural basis for inhibition of chitin synthesis.

DOI: https://doi.org/10.1038/s41586-022-05244-5

Source: https://www.nature.com/articles/s41586-022-05244-5