Activation of Bacterial Cellulose Biosynthesis by Cyclic di-GMP
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Microbes frequently decorate their surfaces with complex carbohydrates to form cell walls, mediate host interactions, or to reduce the efficacies of immune defenses. In a biofilm, bacteria are embedded in a three-dimensional polysaccharide-rich matrix whose formation is often controlled by cyclic di-GMP. In this chapter, I will summarize our current knowledge of the mechanism by which cyclic di-GMP activates bacterial cellulose synthase. Cellulose is a common biofilm component and its biosynthesis is allosterically regulated by cyclic di-GMP. As an exopolysaccharide, cellulose is synthesized and secreted by a membrane-embedded processive glycosyltransferase that contains a C-terminal cyclic di-GMP-binding PilZ domain. Many exopolysaccharide synthases are allosterically regulated by cyclic di-GMP, either by partnering with or being covalently linked to cyclic di-GMP-binding domains. The structural and functional characterizations of Rhodobacter sphaeroides cellulose synthase in resting and activated states provided unique insights into how cyclic di-GMP modulates enzymatic functions. This will be reviewed by discussing (1) biochemical analyses leading to cyclic di-GMP’s discovery and elucidation of its activation mechanism; (2) the structural basis for allosteric activation of cellulose biosynthesis; and (3) additional cyclic di-GMP-regulated control mechanisms of bacterial cellulose synthase complexes.
KeywordsAllosteric activation Biofilm Cellulose synthase Exopolysaccharide