Roberts Alison W, Roberts Eric M, Delmer Deborah P
Department of Biological Sciences, University of Rhode Island, Kingston, Rhode Island 02881, USA.
Eukaryot Cell. 2002 Dec;1(6):847-55. doi: 10.1128/EC.1.6.847-855.2002.
Cellulose, a microfibrillar polysaccharide consisting of bundles of beta-1,4-glucan chains, is a major component of plant and most algal cell walls and is also synthesized by some prokaryotes. Seed plants and bacteria differ in the structures of their membrane terminal complexes that make cellulose and, in turn, control the dimensions of the microfibrils produced. They also differ in the domain structures of their CesA gene products (the catalytic subunit of cellulose synthase), which have been localized to terminal complexes and appear to help maintain terminal complex structure. Terminal complex structures in algae range from rosettes (plant-like) to linear forms (bacterium-like). Thus, algal CesA genes may reveal domains that control terminal complex assembly and microfibril structure. The CesA genes from the alga Mesotaenium caldariorum, a member of the order Zygnematales, which have rosette terminal complexes, are remarkably similar to seed plant CesAs, with deduced amino acid sequence identities of up to 59%. In addition to the putative transmembrane helices and the D-D-D-QXXRW motif shared by all known CesA gene products, M. caldariorum and seed plant CesAs share a region conserved among plants, an N-terminal zinc-binding domain, and a variable or class-specific region. This indicates that the domains that characterize seed plant CesAs arose prior to the evolution of land plants and may play a role in maintaining the structures of rosette terminal complexes. The CesA genes identified in M. caldariorum are the first reported for any eukaryotic alga and will provide a basis for analyzing the CesA genes of algae with different types of terminal complexes.
纤维素是一种由β-1,4-葡聚糖链束组成的微纤维多糖，是植物和大多数藻类细胞壁的主要成分，一些原核生物也能合成纤维素。种子植物和细菌在制造纤维素的膜末端复合物结构上存在差异，进而控制所产生微纤维的尺寸。它们在纤维素合酶催化亚基（CesA基因产物）的结构域结构上也有所不同，该催化亚基已定位到末端复合物，似乎有助于维持末端复合物结构。藻类中的末端复合物结构从玫瑰花结（类似植物）到线性形式（类似细菌）不等。因此，藻类CesA基因可能揭示控制末端复合物组装和微纤维结构的结构域。来自双星藻目成员嗜热微星藻的CesA基因具有玫瑰花结末端复合物，与种子植物的CesA基因非常相似，推导的氨基酸序列同一性高达59%。除了所有已知CesA基因产物共有的假定跨膜螺旋和D-D-D-QXXRW基序外，嗜热微星藻和种子植物的CesA基因还共享植物中保守的区域、N端锌结合结构域和可变或类特异性区域。这表明表征种子植物CesA基因的结构域在陆地植物进化之前就已出现，可能在维持玫瑰花结末端复合物的结构中发挥作用。在嗜热微星藻中鉴定出的CesA基因是首次报道的任何真核藻类的此类基因，将为分析具有不同类型末端复合物的藻类的CesA基因提供基础。
