Observing cellulose biosynthesis and membrane translocation in crystallo
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. Here, in crystallo enzymology with the catalytically...
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Published in | Nature (London) Vol. 531; no. 7594; pp. 329 - 334 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
London
Nature Publishing Group UK
17.03.2016
Nature Publishing Group |
Subjects | |
Online Access | Get full text |
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Summary: | 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. Here,
in crystallo
enzymology with the catalytically active bacterial cellulose synthase BcsA–BcsB 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.
Here the authors use in crystallo enzymology to obtain structural snapshots of a complete cellulose biosynthesis cycle and reveal the mechanism by which the bacterial cellulose synthase BcsA–BcsB translocates the nascent cellulose polymer.
Scenes from cellulose biosynthesis
Cellulose is a long, linear polysaccharide made from D-glucose molecules. It is an important component of plant cell walls and a starting material for the production of many potential biofuels. These authors have used
in crystallo
enzymology to obtain structural snapshots of several steps in the cellulose biosynthesis cycle, including structures of the substrate-bound and product-bound states of the bacterial cellulose synthase BcsA–BcsB complex. And by incubating cellulose-bound BcsA–BcsB with UDP-glucose, they demonstrate polymer elongatation in the crystal. The structures suggest that cellulose is translocated via a ratcheting mechanism involving the up/down movement of a key 'finger helix'. |
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Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division National Cancer Inst. National Inst. of Health AC02-06CH11357; ACB-12002; AGM-12006; P41 GM103403; 1R01GM101001; S10 RR029205; DGE-1315231 National Inst. of General Medical Sciences These authors contributed equally to this work. Present Address: Sandoz GmbH, Biochemiestrasse 10, A-6250 Kundl, Tyrol Austria |
ISSN: | 0028-0836 1476-4687 |
DOI: | 10.1038/nature16966 |