Researchers at the University of Virginia School of Medicine have deciphered the secrets of the production of cellulose, the most common natural polymer on Earth, in a discovery that could have major ramifications for both biofuel production and the battle against bacterial infections.
The findings are of particular interest to the federal Department of Energy, which is seeking ways to break down plant cells more easily to facilitate the production of biofuels. Understanding the production and deposition of cellulose, the primary component of plants’ cell walls, may lead to new ways to tear it down or create plants with weaker walls.
Similarly, the UVA findings may offer new targets for battling bacteria and preventing the spread of infections. Cellulose is one of the components that bacteria produce to create strong, spongy coatings, called biofilms, that let them clump together and cling to surfaces. (The plaque that forms on teeth is a biofilm.) “If we can prevent biofilm formation, we would expect to make it easier to get rid of the bacteria, to actually kill it,” says UVA researcher Jochen Zimmer, D. Phil. “And you could also prevent them from adhering to the surgical devices and other tools used in hospitals.”
A unique enzyme
In a paper published in the prestigious journal Nature , the UVA researchers map out the three-dimensional architecture of the enzyme complex responsible for cellulose production. The researchers first determined the components necessary to produce and secret cellulose and then solved the structure of the enzyme complex. Their study reveals how new cellulose polymers are extruded from a cell through a channel, a bit like a spider spinning a thread of spider silk, and how this process is intimately linked to the formation of cellulose. Until now, the end result was understood but the process itself was largely unknown.
The enzyme is unique in that it both produces cellulose polymers (by attaching glucose molecules) and pushes them outside the cell simultaneously; usually the division of labor is different, with production and movement either handled separately or handled by different enzymes.
“By capturing the crystal structure of part of a protein complex that both synthesizes and transfers cellulose out of a bacterium one sugar unit at a time, this work provides a window into the details of a unique cellular mechanism,” says Pamela Marino, PhD, of the National Institutes of Health’s National Institute of General Medical Sciences, which partly funded the work. “A similar process is likely at work in the synthesis and secretion of key carbohydrate polymers in other organisms, such as hyaluronan in mammals.”
An unexpected observation
In building a three-dimensional model of the atomic architecture of cellulose, the UVA team members were surprised to observe what they had thought almost impossible: they had captured an image of a new cellulose polymer being synthesized and transported from the inside of a cell to the outside. This was most unexpected, both because the process is transitory and because the submicroscopic imaging required – a combination of X-ray diffraction and advanced math – can work only with an extremely stable and uniform ensemble of proteins.
Biofuels, infection prevention … and pest control?
Zimmer expects UVA’s findings to be significant both to biofuel production and the field of medicine, but its impact could reach even further. He says the UVA team plans to extend its research to look at the biosynthesis of chitin, an essential component of the shells of insects. Preventing the formation of chitin, he says, could make for an effective form of pest control.
The UVA paper, authored by Jacob L.W. Morgan, Joanna Strumillo and Jochen Zimmer, has been published online by Nature and will appear in a forthcoming print edition. It is the second article the Department of Molecular Physiology and Biological Physics has had published in Nature since Nov. 15.