德国弗赖堡大学Oliver Einsle团队揭示Shethna蛋白II对钼固氮酶的构象保护。2025年1月8日，国际知名学术期刊《自然》在线发表了这一成果。

研究人员报告了由单粒子冷冻电镜法测定的保护性三元复合物的三维结构，该复合物由钼固氮酶的催化亚单位、其相应的还原酶和FeSII蛋白组成。二聚体FeSII蛋白与每个组分的两个拷贝结合，组装成一个620 kDa的核心复合物，随后聚合成大型的丝状结构。该复合物在催化上不活跃，但酶组分在氧气耗尽后会迅速释放并重新激活。

复合物形成的第一步是FeSII与固氮酶中更易受氧气影响的Fe蛋白组分结合，在突发的氧化压力下保护固氮酶。这个小型铁蛋白的作用代表了一种简单有效的氧气保护机制，这对于转基因固氮酶在食品作物中的维持可能至关重要。

据了解，嗜氧的钼依赖性固氮酶来自Azotobacter vinelandii，通过可逆的“关闭”机制防止氧化损伤。它与小型铁蛋白FeSII（或“Shethna蛋白II”）形成复合物，FeSII作为O₂传感器，当其[2Fe:2S]簇被氧化时，它会与固氮酶的两种组分蛋白结合。

附：英文原文

Title: Conformational protection of molybdenum nitrogenase by Shethna protein II

Author: Franke, Philipp, Freiberger, Simon, Zhang, Lin, Einsle, Oliver

Issue&Volume: 2025-01-08

Abstract: The oxygen-sensitive molybdenum-dependent nitrogenase of Azotobacter vinelandii is protected from oxidative damage by a reversible ‘switch-off’ mechanism1. It forms a complex with a small ferredoxin, FeSII (ref. 2) or the ‘Shethna protein II’3, which acts as an O2 sensor and associates with the two component proteins of nitrogenase when its [2Fe:2S] cluster becomes oxidized4,5. Here we report the three-dimensional structure of the protective ternary complex of the catalytic subunit of Mo-nitrogenase, its cognate reductase and the FeSII protein, determined by single-particle cryo-electron microscopy. The dimeric FeSII protein associates with two copies of each component to assemble a 620kDa core complex that then polymerizes into large, filamentous structures. This complex is catalytically inactive, but the enzyme components are quickly released and reactivated upon oxygen depletion. The first step in complex formation is the association of FeSII with the more O2-sensitive Fe protein component of nitrogenase during sudden oxidative stress. The action of this small ferredoxin represents a straightforward means of protection from O2 that may be crucial for the maintenance of recombinant nitrogenase in food crops.

DOI: 10.1038/s41586-024-08355-3

Source: https://www.nature.com/articles/s41586-024-08355-3