Cellulose-Building Enzyme Uncloaked

Scientists have at last discovered the underlying framework structure of the protein supercomplex that makes cellulose, the biopolymer foundation of plant cell walls. The work led by Purdue University’s Nicholas C. Carpita provides the most detailed glimpse to date of the process by which cellulose is stitched together from glucose molecules. The findings could lead to new ways to engineer plant fibers to make better textiles and easier ways to break down biomass to make fuels and chemicals (Plant Cell 2014, DOI: 10.1105/tpc.114.126862). Cellulose is composed of several dozen strands of glucose sugars linked together in a cablelike structure and condensed into a crystal. The rigidity of cellulose allows plants to stand upright and lends wood its strength. The cellulose-producing protein complex is made of up to 36 individual cellulose synthase enzyme units, each of which synthesizes a glucose chain independently. Carpita and coworkers used small-angle X-ray scattering to show that the enzyme unit is an elongated molecule with a central catalytic domain flanked by two smaller regions. One of the smaller regions couples with a second enzyme to form a dimer. They propose that these dimers organize into larger units that form the overall protein complex.