A protein trisulfide couples dissimilatory sulfate reduction to energy conservation
A protein trisulfide couples dissimilatory sulfate reduction to energy conservation
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DOI：
10.1126/science.aad3558
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发表时间：
2015-12
期刊：
影响因子：
56.9
通讯作者：
A. A. Santos-A.;S. Venceslau;Fabian Grein;W. Leavitt;C. Dahl;D. Johnston;I. Pereira
中科院分区：
文献类型：
--
作者：
A. A. Santos-A.;S. Venceslau;Fabian Grein;W. Leavitt;C. Dahl;D. Johnston;I. Pereira
硫酸盐通过三硫化物还原，微生物可以在没有氧气的情况下呼吸硫化物，最终导致硫化氢的产生。这种古老的新陈代谢在现代缺氧环境中很常见，但酶途径尚未完全解决。通过体内和体外实验，Santos et al.阐明细菌和古细菌中硫酸盐还原途径的酶学(见Fritz和Kroneck的观点)。亚硫酸盐中间体的还原导致两个半胱氨酸残基连接到亚硫酸盐的第三个硫原子，形成三硫产物。由于亚硫酸盐的还原传递了环境中硫的强烈同位素特征，因此同位素分馏模型应该解释这一额外的步骤。科学，这一期，第1541页；另见第1476页，微生物硫酸盐还原通过蛋白质dsrc中的三硫键进行。[另见Fritz和Kroneck的观点]至少25亿年来，微生物硫酸盐还原一直主导着地球的生物地球化学硫循环。然而，这一途径背后的酶机制还不完全清楚，特别是亚硫酸盐的还原，亚硫酸盐是该途径中的关键中间体。这一关键反应是由DsrAB执行的，DsrAB是一种广泛存在的酶，也参与其他异化硫代谢。利用古生菌DsrAB的体外检测，结合细菌系统中的遗传学实验，我们证明了DsrAB还原亚硫酸盐的产物是基于蛋白质的三硫化物，其中亚硫酸盐衍生的硫连接了两个保守的半胱氨酸。生理研究还表明，硫酸盐还原速率是由细胞水平的短链淀粉样蛋白决定的。异化硫酸盐还原将三硫化物的四电子还原与能量守恒结合在一起。
Sulfate reduction via a trisulfide Microorganisms can respire sulfur compounds in the absence of oxygen, eventually leading to the production of hydrogen sulfide. This ancient metabolism is common in modern anoxic environments, but the enzymatic pathways aren't yet fully resolved. Through in vivo and in vitro experiments, Santos et al. clarify the enzymology of the sulfate reduction pathway in both bacteria and archaea (see the Perspective by Fritz and Kroneck). Reduction of the sulfite intermediate results in the linkage of two cysteine residues to a third sulfur atom from sulfite, forming a trisulfide product. Because the reduction of sulfite conveys a strong isotopic signature on sulfur in the environment, isotope fractionation models should account for this additional step. Science, this issue p. 1541; see also p. 1476 Microbial sulfate reduction proceeds through a trisulfide in the protein DsrC. [Also see Perspective by Fritz and Kroneck] Microbial sulfate reduction has governed Earth’s biogeochemical sulfur cycle for at least 2.5 billion years. However, the enzymatic mechanisms behind this pathway are incompletely understood, particularly for the reduction of sulfite—a key intermediate in the pathway. This critical reaction is performed by DsrAB, a widespread enzyme also involved in other dissimilatory sulfur metabolisms. Using in vitro assays with an archaeal DsrAB, supported with genetic experiments in a bacterial system, we show that the product of sulfite reduction by DsrAB is a protein-based trisulfide, in which a sulfite-derived sulfur is bridging two conserved cysteines of DsrC. Physiological studies also reveal that sulfate reduction rates are determined by cellular levels of DsrC. Dissimilatory sulfate reduction couples the four-electron reduction of the DsrC trisulfide to energy conservation.