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Deprecated: Implicit conversion from float 231.6 to int loses precision in C:\Inetpub\vhosts\kidney.de\httpdocs\pget.php on line 534 Nature 2016 ; 531 (7594): 329-34 Nephropedia Template TP
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Observing cellulose biosynthesis and membrane translocation in crystallo #MMPMID26958837
Morgan JL; McNamara JT; Fischer M; Rich J; Chen HM; Withers SG; Zimmer J
Nature 2016[Mar]; 531 (7594): 329-34 PMID26958837show ga
Many biopolymers, including polysaccharides, must be translocated across at least one membrane to reach their site of biological function. Cellulose is a linear glucose polymer synthesized and secreted by a membrane-integrated cellulose synthase. In crystallo enzymology with the catalytically-active bacterial cellulose synthase BcsA-B complex reveals structural snapshots of a complete cellulose biosynthesis cycle, from substrate binding to polymer translocation. Substrate and product-bound structures of BcsA provide the basis for substrate recognition and demonstrate the stepwise elongation of cellulose. Furthermore, the structural snapshots show that BcsA translocates cellulose via a ratcheting mechanism involving a ?finger helix? that contacts the polymer's terminal glucose. Cooperating with BcsA's gating loop, the finger helix moves ?up? and ?down? in response to substrate binding and polymer elongation, respectively, thereby pushing the elongated polymer into BcsA?s transmembrane channel. This mechanism is validated experimentally by tethering BcsA's finger helix, which inhibits polymer translocation but not elongation.