Crystallographic snapshot of cellulose synthesis and membrane translocation.

Cellulose, the most abundant biological macromolecule, is an extracellular, linear polymer of glucose molecules. It represents an essential component of plant cell walls but is also found in algae and bacteria. In bacteria, cellulose production frequently correlates with the formation of biofilms, a sessile, multicellular growth form. Cellulose synthesis and transport across the inner bacterial membrane is mediated by a complex of the multi-spanning catalytic BcsA subunit and the membrane-anchored, periplasmic BcsB protein. Here we present the crystal structure of a complex of BcsA and BcsB from Rhodobacter sphaeroides containing a translocating polysaccharide. The structure of the BcsA-B translocation intermediate reveals the architecture of the cellulose synthase, demonstrates how BcsA forms a cellulose-conducting channel, and suggests a model for the coupling of cellulose synthesis and translocation in which the nascent polysaccharide is extended by one glucose molecule at a time.

纤维素是最丰富的生物大分子，是一种由葡萄糖分子组成的细胞外线性聚合物。它是植物细胞壁的重要组成部分，也存在于藻类和细菌中。在细菌中，纤维素的产生常常与生物膜的形成相关，生物膜是一种固着的多细胞生长形式。纤维素在细菌内膜的合成和运输是由多跨膜催化亚基BcsA和膜锚定的周质蛋白BcsB形成的复合物介导的。在此，我们展示了来自球形红细菌的含有正在转运的多糖的BcsA和BcsB复合物的晶体结构。BcsA - B转运中间体的结构揭示了纤维素合酶的结构，展示了BcsA如何形成一个纤维素传导通道，并提出了一个纤维素合成与转运耦合的模型，在该模型中，新生的多糖一次由一个葡萄糖分子延伸。