Researchers from the Norwegian University of Life Sciences (UMB) have identified an enzyme that can help to break down recalcitrant crystalline polysaccharides such as cellulose and chitin. In a paper in the 8 Oct. issue of the journal Science, the team describes an enzyme that acts on the surface of crystalline chitin, where it introduces chain breaks and generates oxidized chain ends, thus promoting further degradation by chitinases.
The team also found strong indications that similar enzymes exist that work on cellulose. The findings not only demonstrate the existence of a hitherto unknown enzyme activity but also provide new pathways toward more efficient enzymatic conversion of biomass for use in the production of biofuels and biopolymers.
In theory it’s easy to convert the carbohydrates in cellulose, for instance, to small sugar molecules that nourish microorganisms which in turn produce methane and ethanol. But in practice, it has proven to be quite challenging.—Dr. Gustav Vaaje-Kolstad, Norwegian University of Life Sciences
The respective carbohydrate polymers of both chitin and cellulose form extremely dense, resilient bonds. Indeed, the biological function of chitin and cellulose is precisely to make the organism physically hard and durable—slowing the breakdown rate for enzymes whose function is to decompose these kinds of material.
Earlier work by members of the team found that microorganisms that break down chitin produce a protein that increases substrate accessibility and potentiates hydrolytic enzymes. These proteins are classified as carbohydrate-binding modules (CBMs). The first example of such a protein is CBP21 (CBP for chitin-binding protein), produced by the chitinolytic bacterium Serratia marcescens.
We show here that CBP21 is an enzyme that catalyzes cleavage of glycosidic bonds in crystalline chitin, thus opening up the inaccessible polysaccharide material for hydrolysis by normal glycoside hydrolases...In the presence of a reductant such as ascorbic acid, CBP21 boosted chitinase efficiency to much higher levels than previously observed. Biotechnological applications could take advantage of the ability to increase CBP21 activity by adjusting the reaction conditions.
...the reaction catalyzed by CBP21 comprises a hydrolytic step and an oxidation step. We suggest naming CBP21 a “chitin oxidohydrolase.”—Vaaje-Kolstad et al.
To function, the enzymes must be designed to attach securely to the crystalline glucose chains they are intended to break down. This allows them to split the sugars repeatedly without falling off.
Oxidohydrolases could make it both less costly and easier to produce biofuel. They could also serve to scale back the practice of using edible plants as feedstock. The UMB researchers have applied for a patent on their method and are discussing further collaboration with the international enzyme producer Novozymes.
The Research Council of Norway has funded this research through several sources, including the open competitive arena for independent, researcher-initiated basic research projects (FRIPRO) and the research programs on Basic Industry-oriented Biotechnology (GNBIO - terminated), Clean Energy for the Future (RENERGI), and Nature-based Industry (NATUROGNAERING).
Gustav Vaaje-Kolstad, Bjørge Westereng, Svein J. Horn, Zhanliang Liu, Hong Zhai, Morten Sørlie, Vincent G. H. Eijsink (2010) An Oxidative Enzyme Boosting the Enzymatic Conversion of Recalcitrant Polysaccharides. Science Vol. 330. no. 6001, pp. 219 - 222 doi: 10.1126/science.1192231