背景回顾：Cellulose is synthesized by cellulose synthases (CESAs) from the glycosyltransferase GT-2 family. In plants, the CESAs form a six-lobed rosette-shaped CESA complex (CSC). 

主要研究：Here we report crystal structures of the catalytic domain of Arabidopsis thaliana CESA3 (AtCESA3CatD) in both apo and uridine diphosphate (UDP)-glucose (UDP-Glc)–bound forms. 

结果1-AtCESA3CatD结构域：AtCESA3CatD has an overall GT-A fold core domain sandwiched between a plant-conserved region (P-CR) and a class-specific region (C-SR). 

结果2-拟南芥与细菌的CESA3CatD：By superimposing the structure of AtCESA3CatD onto the bacterial cellulose synthase BcsA, we found that the coordination of the UDP-Glc differs, indicating different substrate coordination during cellulose synthesis in plants and bacteria. 

结果3-beta链与同源二聚化：Moreover, structural analyses revealed that AtCESA3CatD can form a homodimer mainly via interactions between specific beta strands. 

结果4-实验验证beta链的重要性：We confirmed the importance of specific amino acids on these strands for homodimerization through yeast and in planta assays using point-mutated full-length AtCESA3. 

结论：Our work provides molecular insights into how the substrate UDP-Glc is coordinated in the CESAs and how the CESAs might dimerize to eventually assemble into CSCs in plants.

 摘 要 

纤维素是由糖基转移酶GT-2家族的纤维素合酶CESAs合成的。在植物中，CESAs组成一个六瓣莲座状CESA复合体CSC。本文中，作者报道了无核苷酸结合（apo）以及UDP-Glc结合状态下的拟南芥CESA3酶催化结构域的晶体结构。AtCESA3CatD在植物保守区（P-CR）和支系特异区（C-SR）之间存在一个GT-A折叠核心结构域。通过将AtCESA3CatD的结构叠加到细菌纤维素合酶BcsA上，作者发现UDP-Glc的配位不同，表明植物和细菌在纤维素合成过程中的底物配位不同。此外，结构分析显示AtCESA3CatD主要通过特定β链之间的相互作用形成同型二聚体。作者基于点突变的全长AtCESA3，通过酵母和植物体内试验，证实了这些β链上的特定氨基酸对于AtCESA3CatD同源二聚化的重要性。本文的研究揭示了底物UDP-Glc在CESAs中的配位以及CESAs如何二聚化、从而最终组装成CSCs的分子机制。