Structural and Mechanistic Features of Bacterial Cellulose Synthesis.
Major advances in the knowledge of bacterial cellulose biosynthesis along with the formation of biofilm have been made throughout the elucidation of the crystalline complex of two enzymes involved in the polymerization and the translocation of the polysaccharide. Cellulose is synthesized by membrane-embedded glycosyltransferases that processively polymerize UDP-activated glucose. Polymer synthesis is coupled to membrane translocation through a channel formed by the cellulose synthase. Two enzymes (BcsA and BcsB from Rhodobacter sphaeroides) form the catalytically active core of bacterial cellulose synthase sufficient for in vitro cellulose synthesis. The purified BcsA-BcsB complex produces cellulose chains of a degree of polymerization in the range 200-300.
The structure of the BcsA-BcsB 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. The dissection of the catalytic mechanism provides a foundation for the synthesis of biofilm exopolysaccharides.