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Nat Struct Mol Biol. 2014 May;21(5):489-96. doi: 10.1038/nsmb.2803. Epub 2014 Apr 6.

Mechanism of activation of bacterial cellulose synthase by cyclic di-GMP.

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Center for Membrane Biology, Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia, USA.


The bacterial signaling molecule cyclic di-GMP (c-di-GMP) stimulates the synthesis of bacterial cellulose, which is frequently found in biofilms. Bacterial cellulose is synthesized and translocated across the inner membrane by a complex of cellulose synthase BcsA and BcsB subunits. Here we present crystal structures of the c-di-GMP-activated BcsA-BcsB complex. The structures reveal that c-di-GMP releases an autoinhibited state of the enzyme by breaking a salt bridge that otherwise tethers a conserved gating loop that controls access to and substrate coordination at the active site. Disrupting the salt bridge by mutagenesis generates a constitutively active cellulose synthase. Additionally, the c-di-GMP-activated BcsA-BcsB complex contains a nascent cellulose polymer whose terminal glucose unit rests at a new location above BcsA's active site and is positioned for catalysis. Our mechanistic insights indicate how c-di-GMP allosterically modulates enzymatic functions.

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