28.06.2021

Modular enzymes for hemicellulose synthesis.

Fiber, food, fuel - the carbohydrate polymers that encapsulate plants cells have benefited humans for centuries. Arguably the most prominent of these is cellulose, a linear polymer made of glucose moieties that stabilizes the cell wall. But stability would not be perfect without the cross-linking hemicelluloses, which are branched polymers made of different sugar moieties like, e.g., glucose, arabinose, and mannose. They can be extracted from wood, but comparatively little is known about how these polymers can be reconstituted and modulated in cells suitable for biotechnological purposes. Scientists from the IPB together with colleagues from the University of Düsseldorf could now move biotechnological hemicellulose production a step forward.

The researchers assembled cellulose synthase-like A (CSLA) enzymes from different plant species to produce tunable heteromannan (HM) polysaccharides in the Pichia pastoris yeast expression system. For that, they used an enzyme from Arabidopsis thaliana that is thought to preferably synthesize pure mannan, and one derived from Amorphophallus konjac that is thought to be primarliy a glucomannan synthase. They swapped the domains of these synthases and investigated firstly, how the resulting chimeras affect yeast viability during expression, and secondly, how HM produced by these chimeras were composed.

The researchers found that prolonged expression of the A. konjac glucomannan synthase impaired yeast biomass accumulation and ultimately cell viability. However, when swapping the C-terminal region for that of the A. thaliana enzyme, the resulting engineered glucomannan synthase did not inhibit yeast growth and showed increased HM production. Apart from that, two additional chimeric CSLA enzymes with higher β-1,4-linked mannan production than the parental enzymes and minimal detriment to yeast growth could be identified. Furthermore, the researchers found that HM yield and glucose incorporation could be increased when a co-factor from Arabidopsis was co-expressed with the chimeric CSLA proteins.

Hemicelluloses exhibit suitable chemico-physical properties for use as biopolymers in food, drug and cosmetics. This study opens novel routes for the production and engineering of polysaccharide-based biomaterials to advance a sustainable bioeconomy.

Original publication:
Robert, M., Waldhauer, J., Stritt, F. et al. Modular biosynthesis of plant hemicellulose and its impact on yeast cells. Biotechnol Biofuels 14, 140 (2021). https://doi.org/10.1186/s13068-021-01985-z