Ho Ruoya, Purushotham Pallinti, Wilson Louis F L, Wan Yueping, Zimmer Jochen
Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, United States.
Howard Hughes Medical Institute, Chevy Chase, United States.
Elife. 2025 May 14;13:RP96704. doi: 10.7554/eLife.96704.
Plant cell walls contain a meshwork of cellulose fibers embedded into a matrix of other carbohydrate and non-carbohydrate-based biopolymers. This composite material exhibits extraordinary properties, from stretchable and pliable cell boundaries to solid protective shells. Cellulose, a linear glucose polymer, is synthesized and secreted across the plasma membrane by cellulose synthase (CesA), of which plants express multiple isoforms. Different subsets of CesA isoforms are necessary for primary and secondary cell wall biogenesis. Here, we structurally and functionally characterize the (soybean) primary cell wall CesAs CesA1, CesA3, and CesA6. The CesA isoforms exhibit robust in vitro catalytic activity. Cryo-electron microscopy analyses reveal their assembly into homotrimeric complexes in vitro in which each CesA protomer forms a cellulose-conducting transmembrane channel with a large lateral opening. Biochemical and co-purification analyses demonstrate that different CesA isoforms interact in vitro, leading to synergistic cellulose biosynthesis. Interactions between CesA trimers are only observed between different CesA isoforms and require the class-specific region (CSR). The CSR forms a hook-shaped extension of CesA's catalytic domain at the cytosolic water-lipid interface. Negative stain and cryo-electron microscopy analyses of mixtures of different CesA isoform trimers reveal their side-by-side arrangement into loose clusters. Our data suggest a model by which CesA homotrimers of different isoforms assemble into cellulose synthase complexes to synthesize and secrete multiple cellulose chains for microfibril formation. Inter-trimer interactions are mediated by fuzzy interactions between their CSR extensions.
植物细胞壁包含一个纤维素纤维网络，这些纤维嵌入到由其他碳水化合物和非碳水化合物基生物聚合物组成的基质中。这种复合材料具有非凡的特性，从可拉伸且柔韧的细胞边界到坚固的保护壳。纤维素是一种线性葡萄糖聚合物，由纤维素合酶（CesA）在质膜上合成并分泌，植物中表达多种CesA同工型。不同的CesA同工型亚群对于初生和次生细胞壁的生物合成是必需的。在这里，我们对大豆初生细胞壁的CesA1、CesA3和CesA6进行了结构和功能表征。这些CesA同工型在体外表现出强大的催化活性。冷冻电子显微镜分析揭示了它们在体外组装成同三聚体复合物，其中每个CesA原体形成一个具有大侧向开口的纤维素传导跨膜通道。生化和共纯化分析表明，不同的CesA同工型在体外相互作用，导致协同的纤维素生物合成。仅在不同的CesA同工型之间观察到CesA三聚体之间的相互作用，并且需要类特异性区域（CSR）。CSR在胞质水 - 脂界面形成CesA催化结构域的钩状延伸。对不同CesA同工型三聚体混合物的负染色和冷冻电子显微镜分析揭示了它们并排排列成松散的簇。我们的数据提出了一个模型，通过该模型不同同工型的CesA同三聚体组装成纤维素合酶复合物，以合成和分泌多条纤维素链用于微纤丝的形成。三聚体间的相互作用由它们CSR延伸之间的模糊相互作用介导。
