Molecules 10,000 times narrower than human hair key to wooden skyscrapers
The study, led by a father and son team at the Universities of Warwick and Cambridge, solves a long-standing mystery of how key sugars in cells bind to form strong, indigestible materials.
The two most common large molecules – or ‘polymers’ – found on Earth are cellulose and xylan, both of which are found in the cell walls of materials such as wood and straw. They play a key role in determining the strength of materials and how easily they can be digested.
For some time, scientists have known that these two polymers must somehow stick together to allow the formation of strong plant walls, but how this occurs has, until now, remained a mystery: xylan is a long, winding polymer with so-called ‘decorations’ of other sugars and molecules attached, so how could this adhere to the thick, rod-like cellulose molecules?
“We knew the answer must be elegant and simple,” explains Professor Paul Dupree from the Department of Biochemistry at the University of Cambridge, who led the research.
“And in fact, it was. What we found was that cellulose induces xylan to untwist itself and straighten out, allowing it to attach itself to the cellulose molecule. It then acts as a kind of ‘glue’ that can protect cellulose or bind the molecules together, making very strong structures.”
The finding was made possible due to an unexpected discovery several years ago in Arabidopsis, a small flowering plant related to cabbage and mustard.
Professor Dupree and colleagues showed that the decorations on xylan can only occur on alternate sugar molecules within the polymer – in effect meaning that the decorations only appear on one side of xylan.
This led the team of researchers to survey other plants in the Cambridge University Botanic Garden and discover that the phenomenon appears to occur in all plants, meaning it must have evolved in ancient times, and must be important.
To explore this in more detail, they turned to an imaging technique known as solid state nuclear magnetic resonance (ssNMR), which is based on the same physics as hospital MRI scanners, but can reveal structure at the nanoscale.
However, while ssNMR can image carbon, it requires a particular heavy isotope of carbon, carbon-13. This meant that the team had to grow their plants in an atmosphere enriched with a special form of carbon dioxide – carbon-13 dioxide.
Professor Ray Dupree of the University of Warwick – Paul Dupree’s father, and a co-author on the paper – supervised the work at Warwick’s ssNMR laboratory: “By studying these molecules, which are over 10,000 times narrower than the width of a human hair, we could see for the first time how cellulose and xylan slot together and why this makes for such strong cell walls.” ■
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