Cellulosomes are large, multiprotein complexes that tether plant biomass-degrading enzymes together for improved hydrolysis¹. These complexes were first described in anaerobic bacteria, where species-specific dockerin domains mediate the assembly of enzymes onto cohesin motifs interspersed within protein scaffolds¹. The versatile protein assembly mechanism conferred by the bacterial cohesin-dockerin interaction is now a standard design principle for synthetic biology^2,3. For decades, analogous structures have been reported in anaerobic fungi, which are known to assemble by sequence-divergent non-catalytic dockerin domains (NCDDs)⁴. However, the components, modular assembly mechanism and functional role of fungal cellulosomes remain unknown^5,6. Here, we describe a comprehensive set of proteins critical to fungal cellulosome assembly, including conserved scaffolding proteins unique to the Neocallimastigomycota. High-quality genomes of the anaerobic fungi Anaeromyces robustus, Neocallimastix californiae and Piromyces finnis were assembled with long-read, single-molecule technology. Genomic analysis coupled with proteomic validation revealed an average of 312 NCDD-containing proteins per fungal strain, which were overwhelmingly carbohydrate active enzymes (CAZymes), with 95 large fungal scaffoldins identified across four genera that bind to NCDDs. Fungal dockerin and scaffoldin domains have no similarity to their bacterial counterparts, yet several catalytic domains originated via horizontal gene transfer with gut bacteria. However, the biocatalytic activity of anaerobic fungal cellulosomes is expanded by the inclusion of GH3, GH6 and GH45 enzymes. These findings suggest that the fungal cellulosome is an evolutionarily chimaeric structure-an independently evolved fungal complex that co-opted useful activities from bacterial neighbours within the gut microbiome.

中文翻译：

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比较基因组学揭示了真菌纤维素的零件清单。

纤维素是一种大型的多蛋白复合物，可将植物生物质降解酶束缚在一起，以改善水解¹。这些复合物首先在厌氧细菌中描述，其中物种特异性的dockerin结构域介导酶组装到散布在蛋白质支架^1中的凝聚素基序上。由细菌cohesin-dockerin相互作用赋予的多功能蛋白质组装机制现在是合成生物学^2,3的标准设计原则。数十年来，已经报道了厌氧真菌中的类似结构，已知该结构是通过序列不同的非催化dockerin域（NCDD）组装而成的⁴。然而，真菌纤维素的成分，模块组装机制和功能作用仍未知^5,6。在这里，我们描述了一套完整的对真菌纤维素组装至关重要的蛋白质，其中包括新愈伤放线菌特有的保守支架蛋白质。厌氧真菌鲁氏厌氧菌，加利福尼亚新callimastix和芬兰毕氏酵母的高质量基因组是通过长期阅读的单分子技术组装而成的。基因组分析和蛋白质组学验证表明，每个真菌菌株平均含有312种含NCDD的蛋白质，其中绝大多数是碳水化合物活性酶（CAZymes），在与NCDD结合的四个属中鉴定出95种大型真菌支架素。真菌的dockerin和scaffoldin域与细菌的对应域没有相似之处，但是一些催化域是通过肠道细菌水平基因转移而产生的。然而，GH3，GH6和GH45酶的加入扩大了厌氧真菌纤维素酶的生物催化活性。这些发现表明真菌纤维素体是一种进化的嵌合体结构-一种独立进化的真菌复合体，它从肠道微生物组内的细菌邻居中选择了有用的活性。