Dussouchaud Macha, Martinez-Carranza Markel, Garcia Pierre-Simon, Clémancey Martin, Blondin Geneviève, Betton Jean Michel, Haouz Ahmed, Gribaldo Simonetta, Ollagnier de Choudens Sandrine, Sauguet Ludovic, Mechaly Ariel, Barras Frédéric
Department of Microbiology, Unit Stress Adaptation and Metabolism in Enterobacteria, Institut Pasteur, Université Paris Cité, UMR CNRS 6047, Paris, France.
Department of Structural Biology, Unit Architecture and Dynamics of Biological Macromolecules, Institut Pasteur, Université Paris Cité, UMR CNRS 3528, Paris, France.
PLoS Biol. 2025 Jun 25;23(6):e3003223. doi: 10.1371/journal.pbio.3003223. eCollection 2025 Jun.
[Fe-S] clusters are ancient and ubiquitous protein co-factors, which contributed to the emergence of life in an anoxic planet. We have recently identified two minimal [Fe-S] biogenesis systems, MIS and SMS, inferred to be ancestral systems dating back to the Last Universal Common Ancestor and which gave rise to the well-studied modern Iron-Sulfur Cluster (ISC), Nitrogen Fixation (NIF), and Sulfur Mobilization (SUF) machineries. The present study focuses on the ancestor SMS from the hyperthermophilic archaeon Methanocaldococcus jannaschii. Biochemical and structural studies showed that SMS is made of a SmsC2B2 heterotetratmer wherein the SmsC subunit hosts both ATP and [Fe-S] cluster binding sites. Binding of ATP and assembly of [Fe-S] were found to be mutually exclusive allowing for a regulatory coupling between binding of both substrates. Mutagenesis and in vitro transfer experiments revealed the key role of SmsC-contained Cys residues in cluster assembly. Strikingly, the SMS system rescued a non-viable Escherichia coli strain lacking endogenous ISC and SUF systems grown under anoxic conditions, in the presence of Na2S, indicating that sulfide is a source of sulfur for SMS. In addition, we predict that most archaea SmsC proteins hold a similar C-terminal [Fe-S] cluster assembly site. Taking into account those unique structural and functional features, we propose a mechanistic model describing how SmsC2B2 assembles and distributes [4Fe-4S] clusters. Altogether this study established SMS as a new bona fide [Fe-S] biogenesis system that operated in anaerobic prokaryotes prior to evolve to SUF after the Great Oxydation Event.
[铁硫]簇是古老且普遍存在的蛋白质辅因子，在缺氧星球上对生命的出现起到了推动作用。我们最近鉴定出了两个最小的[铁硫]生物合成系统，即MIS和SMS，据推测它们是可追溯到最后共同祖先的原始系统，并且衍生出了经过充分研究的现代铁硫簇（ISC）、固氮（NIF）和硫动员（SUF）机制。本研究聚焦于嗜热古菌詹氏甲烷球菌的原始SMS系统。生化和结构研究表明，SMS由SmsC2B2异源四聚体组成，其中SmsC亚基同时拥有ATP和[铁硫]簇结合位点。发现ATP的结合与[铁硫]簇的组装相互排斥，从而实现了两种底物结合之间的调节偶联。诱变和体外转移实验揭示了SmsC中所含半胱氨酸残基在簇组装中的关键作用。引人注目的是，在存在Na2S的情况下，SMS系统挽救了在缺氧条件下生长的缺乏内源性ISC和SUF系统的非存活大肠杆菌菌株，这表明硫化物是SMS的硫源。此外，我们预测大多数古菌SmsC蛋白具有类似的C端[铁硫]簇组装位点。考虑到这些独特的结构和功能特征，我们提出了一个描述SmsC2B2如何组装和分布[4Fe-4S]簇的机制模型。总之，本研究将SMS确立为一种新的真正的[铁硫]生物合成系统，该系统在厌氧原核生物中运行，在大氧化事件后进化为SUF之前。
