National Key Laboratory of Crop Genetic Improvement and National Centre of Plant Gene Research, Huazhong Agricultural University, Wuhan, China.
Plant Biotechnol J. 2021 Aug;19(8):1579-1587. doi: 10.1111/pbi.13571. Epub 2021 Apr 5.
Cellulose is one of the most abundant organic polymers in nature. It contains multiple β-1,4-glucan chains synthesized by cellulose synthases (CesAs) on the plasma membrane of higher plants. CesA subunits assemble into a pseudo-sixfold symmetric cellulose synthase complex (CSC), known as a 'rosette complex'. The structure of CesA remains enigmatic. Here, we report the cryo-EM structure of the homotrimeric CesA7 from Gossypium hirsutum at 3.5-angstrom resolution. The GhCesA7 homotrimer shows a C3 symmetrical assembly. Each protomer contains seven transmembrane helices (TMs) which form a channel potentially facilitating the release of newly synthesized glucans. The cytoplasmic glycosyltransferase domain (GT domain) of GhCesA7 protrudes from the membrane, and its catalytic pocket is directed towards the TM pore. The homotrimer GhCesA7 is stabilized by the transmembrane helix 7 (TM7) and the plant-conserved region (PCR) domains. It represents the building block of CSCs and facilitates microfibril formation. This structure provides insight into how eukaryotic cellulose synthase assembles and provides a mechanistic basis for the improvement of cotton fibre quality in the future.
纤维素是自然界中最丰富的有机聚合物之一。它包含由高等植物质膜上的纤维素合酶（CesAs）合成的多个β-1,4-葡聚糖链。CesA 亚基组装成具有假六重对称的纤维素合酶复合物（CSC），称为“玫瑰花结复合物”。CesA 的结构仍然是个谜。在这里，我们报告了棉花（Gossypium hirsutum）同源三聚体 CesA7 的冷冻电镜结构，分辨率为 3.5 埃。GhCesA7 同源三聚体显示 C3 对称组装。每个原体包含七个跨膜螺旋（TM），形成一个可能促进新合成葡聚糖释放的通道。GhCesA7 的细胞质糖基转移酶结构域（GT 结构域）从膜中突出，其催化口袋朝向 TM 孔。同源三聚体 GhCesA7 由跨膜螺旋 7（TM7）和植物保守区（PCR）结构域稳定。它代表 CSCs 的构建块，并促进微纤维的形成。该结构提供了对真核纤维素合酶组装的深入了解，并为未来提高棉花纤维质量提供了机制基础。
