A new, super-sensitive instrument lets scientists see where a protein binds to plant cell walls, which loosens them and makes growth possible.
Researchers say the discovery could one day lead to bigger harvests of biomass for renewable energy.
Finding that binding target has been a major challenge for structural biologists. That’s because there are only tiny amounts of the protein involved in cell growth and because cell walls are very complex, says Mei Hong, one of the project’s lead researchers, a professor of chemistry at Iowa State University.
A paper describing the discovery appears early online in the Proceedings of the National Academy of Sciences.
Hong has long used solid-state nuclear magnetic resonance (NMR) spectroscopy to study structural biology, including the mechanism used by the flu virus to infect host cells. But in this case, that technology wasn’t sensitive enough to identify the binding site of the expansin protein.
So the researchers—working with specialists from the Bruker BioSpin Corp., a manufacturer of scientific instruments—used a technology called dynamic nuclear polarization (DNP), to enhance the sensitivity of spectroscopy instruments.
The researchers studied Arabidopsis thaliana, often used as a model subject in plant science studies, and found the protein binds to specific regions of cellulose microfibrils, the long, parallel chains of cellulose that make up plant cell walls. The action weakens the network formed by a cell wall’s cellulose, hemicellulose, and pectins, loosening the cell wall and allowing cell growth.
The researchers found the target site is the part of the cellulose microfibril that is enriched with the hemicellulose xyloglucan. The target site has a different cellulose structure than a plant’s bulk cellulose.
“This result wasn’t trivial to get and we are quite happy that the DNP NMR technology is so useful for understanding this plant biochemistry question,” says Hong, also a faculty scientist with the US Department of Energy’s Ames Laboratory.
And yes, she says, “Our result could be exploited for practical benefits.” Knowing where expansin binds to cell walls “might help biochemists design more potent expansins to loosen the cell wall and stimulate plant growth and thus better harvest bioenergy.”
Hong and Daniel Cosgrove, professor and chair in biology at Penn State, are the lead authors. Additional researchers contributed from Iowa State, Penn State, and Broker BioSpin Corp. The US Department of Energy supported the work.
Source: Iowa State