Septins是膜相关的细胞骨架鸟嘌呤-核苷酸结合蛋白家族,在各种细胞过程中起着至关重要的作用。比如细胞分裂,吞噬作用,和细胞器裂变。尽管它们很重要,septins的进化起源和祖先功能尚不清楚。在opisthokonts,隔膜形成五个不同的直系同源物,来自多个基团的亚基组装成杂聚物,从而支持它们不同的分子功能。最近的研究表明,在藻类和原生生物中,表明来自最后一个真核生物共同祖先的古老起源。然而,真核生物中septin之间的系统发育关系尚不清楚。这里,我们扩展了非opisthokonseptins的列表,包括以前无法识别的来自蓝藻藻的隔膜。构建254个总隔膜的生根系统发育树,我们观察到主要的非opisthokont和opisthokont分离枝之间的分叉。在非opisthokont隔膜中,我们确定了三个主要的子分支:代表绿藻绿藻的第6组(6A主要用于具有单个隔膜的物种,6B用于具有多个隔膜的物种),第7组代表绿藻中的藻类,异性恋者,haptophytes,菊科植物,和红藻,第8组代表纤毛虫。蓝藻植物和一些纤毛隔膜在所有其他隔膜和外群之间形成了孤儿谱系。结合祖先序列重建和AlphaFold预测,我们追踪了真核生物中septins的结构进化。在GTPase结构域中,在大多数藻类和纤毛虫物种中,我们在至少一个隔膜的G界面内发现了保守的GAP样精氨酸指。此残留物是单个衣藻分离的同源二聚化所必需的,它的丢失与各种谱系的septin复制事件相吻合。精氨酸指的丢失通常伴随着α0螺旋的出现,已知的NC接口交互主题,潜在的标志着septin-septin相互作用机制从同源二聚化到异源寡聚化的多样化。最后,我们在所有间隔组中发现了两亲螺旋,表明膜结合是一种祖先特征。卷曲螺旋结构域也分布广泛,而在6A和7组的一些隔膜中发现了跨膜结构域。总之,这项研究提高了我们对间隔分布和系统发育分组的理解,照亮他们祖先的特征,势函数,早期进化。
Septins are a family of membrane-associated cytoskeletal guanine-nucleotide binding proteins that play crucial roles in various cellular processes, such as cell division, phagocytosis, and organelle fission. Despite their importance, the evolutionary origins and ancestral function of septins remain unclear. In opisthokonts, septins form five distinct groups of orthologs, with subunits from multiple groups assembling into heteropolymers, thus supporting their diverse molecular functions. Recent studies have revealed that septins are also conserved in algae and protists, indicating an ancient origin from the last eukaryotic common ancestor. However, the phylogenetic relationships among septins across eukaryotes remained unclear. Here, we expanded the list of non-opisthokont septins, including previously unrecognized septins from glaucophyte algae. Constructing a rooted phylogenetic tree of 254 total septins, we observed a bifurcation between the major non-opisthokont and opisthokont septin clades. Within the non-opisthokont septins, we identified three major subclades: Group 6 representing chlorophyte green algae (6A mostly for species with single septins, 6B for species with multiple septins), Group 7 representing algae in chlorophytes, heterokonts, haptophytes, chrysophytes, and rhodophytes, and Group 8 representing ciliates. Glaucophyte and some ciliate septins formed orphan lineages in-between all other septins and the outgroup. Combining ancestral-sequence reconstruction and AlphaFold predictions, we tracked the structural evolution of septins across eukaryotes. In the GTPase domain, we identified a conserved GAP-like arginine finger within the G-interface of at least one septin in most algal and ciliate species. This residue is required for homodimerization of the single Chlamydomonas septin, and its loss coincided with septin duplication events in various lineages. The loss of the arginine finger is often accompanied by the emergence of the α0 helix, a known NC-interface interaction motif, potentially signifying the diversification of septin-septin interaction mechanisms from homo-dimerization to hetero-oligomerization. Lastly, we found amphipathic helices in all septin groups, suggesting that membrane binding is an ancestral trait. Coiled-coil domains were also broadly distributed, while transmembrane domains were found in some septins in Group 6A and 7. In summary, this study advances our understanding of septin distribution and phylogenetic groupings, shedding light on their ancestral features, potential function, and early evolution.