New insights into the enzymes that breakdown starches and cellulose for biofuel production

Breaking apart polysaccharides such as starches and cellulose in a cost-effective way is one of the biggest challenges facing biofuels scientists. Now, a team of scientists from the Los Alamos National Laboratory has mapped the three-dimensional structure of a protein that breaks down the enzyme, something which could lead to a drastic reduction in the costs of biofuel production.

The research focused specifically on a class of copper-dependent enzymes called lytic polysaccharide monooxygenases (LPMOs), which bacteria and fungi use to naturally break down cellulose and closely related chitin biopolymers.

“In the long term, understanding the mechanism of this class of proteins can lead to enzymes with improved characteristics that make production of ethanol increasingly economically feasible,” said Julian Chen, a Los Alamos National Laboratory scientist who participated in the research.

A team from a mix of Norwegian and US institutions used the neutron scattering facility at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory and the Advanced Light Source (ALS) synchrotron X-ray source at Lawrence Berkeley National Laboratory to study LPMO. LPMO enzymes use a single copper ion to activate oxygen, a critical step for the enzyme’s catalytic degrading action.

Specific mechanisms of the LPMO action remain uncertain, but it is thought that catalysis involves initial formation of a superoxide by electron transfer from the reduced copper ion. By understanding the location of the copper ion and the constellation of atoms near it, the researchers hope to learn more about the enzyme’s function. For this to happen however, the team needed to learn as much as possible about the structure of the enzyme.

The new study, published in the journal Biochemistry, has presented one of the most comprehensive structures of the LPMO enzyme to date, catching it ‘in the act’ of binding oxygen. Combined with previous research, the new study points to a common mechanism of degrading cellulosic biomass among different bacteria and fungi, despite wide differences in their protein sequences.