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Title: Structure of the cellulose synthase complex of Gluconacetobacter hansenii at 23.4 Å resolution

Bacterial crystalline cellulose is used in biomedical and industrial applications, but the molecular mechanisms of synthesis are unclear. Unlike most bacteria, which make non-crystalline cellulose, Gluconacetobacter hansenii extrudes profuse amounts of crystalline cellulose. Its cellulose synthase (AcsA) exists as a complex with accessory protein AcsB, forming a 'terminal complex' (TC) that has been visualized by freeze-fracture TEM at the base of ribbons of crystalline cellulose. The catalytic AcsAB complex is embedded in the cytoplasmic membrane. The C-terminal portion of AcsC is predicted to form a translocation channel in the outer membrane, with the rest of AcsC possibly interacting with AcsD in the periplasm. It is thus believed that synthesis from an organized array of TCs coordinated with extrusion by AcsC and AcsD enable this bacterium to make crystalline cellulose. The only structural data that exist for this system are the above mentioned freeze-fracture TEM images, fluorescence microscopy images revealing that TCs align in a row, a crystal structure of AcsD bound to cellopentaose, and a crystal structure of PilZ domain of AcsA. Here we advance our understanding of the structural basis for crystalline cellulose production by bacterial cellulose synthase by determining a negative stain structure resolved to 23.4 angstrom formore » highly purified AcsAB complex that catalyzed incorporation of UDP-glucose into β-1,4-glucan chains, and responded to the presence of allosteric activator cyclic diguanylate. Although the AcsAB complex was functional in vitro, the synthesized cellulose was not visible in TEM. The negative stain structure revealed that AcsAB is very similar to that of the BcsAB synthase of Rhodobacter sphaeroides, a non-crystalline cellulose producing bacterium. Furthermore, the results indicate that the crystalline cellulose producing and non-crystalline cellulose producing bacteria share conserved catalytic and membrane translocation components, and support the hypothesis that it is the extrusion mechanism and order in linearly arrayed TCs that enables production of crystalline cellulose.« less
 [1] ;  [2] ;  [1] ;  [3] ;  [1] ;  [1]
  1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Biochemistry & Molecular Biology
  2. Pennsylvania State Univ., University Park, PA (United States). Dept. of Biochemistry & Molecular Biology; Dept. of Environmental Protection (DEP-PA), Harrisburg, PA (United States). Biological Services Section, Bureau of Lab. (BOL)
  3. Pennsylvania State Univ., University Park, PA (United States). Dept. of Chemical Engineering
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Additional Journal Information:
Journal Volume: 11; Journal Issue: 5; Journal ID: ISSN 1932-6203
Public Library of Science
Research Org:
Pennsylvania State Univ., University Park, PA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
59 BASIC BIOLOGICAL SCIENCES; particle electron cryomicroscopy; cyclic diguanylic acid; gmp-binding protein; in-vitro synthesis; acetobacter-xylinum; bacterial cellulose; di-gmp; outer-membrane; biosynthesis; subunit
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OSTI ID: 1282049