Ross P, Mayer R, Benziman M
Departement of Biological Chemistry, Hebrew University of Jerusalem, Israel.
Microbiol Rev. 1991 Mar;55(1):35-58. doi: 10.1128/mr.55.1.35-58.1991.
The current model of cellulose biogenesis in plants, as well as bacteria, holds that the membranous cellulose synthase complex polymerizes glucose moieties from UDP-Glc into beta-1,4-glucan chains which give rise to rigid crystalline fibrils upon extrusion at the outer surface of the cell. The distinct arrangement and degree of association of the polymerizing enzyme units presumably govern extracellular chain assembly in addition to the pattern and width of cellulose fibril deposition. Most evident for Acetobacter xylinum, polymerization and assembly appear to be tightly coupled. To date, only bacteria have been effectively studied at the biochemical and genetic levels. In A. xylinum, the cellulose synthase, composed of at least two structurally similar but functionally distinct subunits, is subject to a multicomponent regulatory system. Regulation is based on the novel nucleotide cyclic diguanylic acid, a positive allosteric effector, and the regulatory enzymes maintaining its intracellular turnover: diguanylate cyclase and Ca2(+)-sensitive bis-(3',5')-cyclic diguanylic acid (c-di-GMP) phosphodiesterase. Four genes have been isolated from A. xylinum which constitute the operon for cellulose synthesis. The second gene encodes the catalytic subunit of cellulose synthase; the functions of the other three gene products are still unknown. Exclusively an extracellular product, bacterial cellulose appears to fulfill diverse biological roles within the natural habitat, conferring mechanical, chemical, and physiological protection in A. xylinum and Sarcina ventriculi or facilitating cell adhesion during symbiotic or infectious interactions in Rhizobium and Agrobacterium species. A. xylinum is proving to be most amenable for industrial purposes, allowing the unique features of bacterial cellulose to be exploited for novel product applications.
目前关于植物以及细菌中纤维素生物合成的模型认为，膜状纤维素合酶复合体将UDP - 葡萄糖中的葡萄糖部分聚合成β - 1,4 - 葡聚糖链，这些链在细胞外表面挤出时形成刚性结晶纤维。聚合酶单元的独特排列和结合程度除了决定纤维素纤维沉积的模式和宽度外，可能还控制着细胞外链的组装。对于木醋杆菌来说，聚合和组装似乎紧密相连。迄今为止，仅在生化和遗传水平上对细菌进行了有效的研究。在木醋杆菌中，纤维素合酶由至少两个结构相似但功能不同的亚基组成，受多组分调节系统调控。调节基于新型核苷酸环二鸟苷酸（一种正变构效应物）以及维持其细胞内周转的调节酶：二鸟苷酸环化酶和Ca2(+)敏感的双（3',5'） - 环二鸟苷酸（c - di - GMP）磷酸二酯酶。已从木醋杆菌中分离出四个基因，它们构成了纤维素合成操纵子。第二个基因编码纤维素合酶的催化亚基；其他三个基因产物的功能仍不清楚。细菌纤维素完全是一种细胞外产物，在自然生境中似乎发挥着多种生物学作用，在木醋杆菌和八叠球菌中提供机械、化学和生理保护，或在根瘤菌和土壤杆菌的共生或感染性相互作用中促进细胞黏附。事实证明木醋杆菌非常适合工业用途，可利用细菌纤维素的独特特性开发新产品应用。
