Tuesday, 23 February, 2021

Duality in cellulose-degrading complexes

Using single-molecule fluorescence techniques, scientists at the LMU has discovered how cellulose-degrading complexes arrange themselves for optimal efficiency and how they change their enzymatic composition to adapt to their substrate. Plants produce over 200 billion tons of cellulose per year, making cellulose the most abundant biomolecule on earth. Lignocellulose represents a virtual unlimited renewable stock for the production biofuel, but the degradation into its constitute sugars is a very difficult task.

Produced by some bacteria, cellulosomes are the most efficient machinery for the degradation of lignocellulose. “Cellulosomes are like molecular Legos, where you can plug diverse type of cellulolytic enzymes. It is the combination of all of these diverse enzymes working together what makes these complexes that good in degrading cellulose”, says Andrés Vera, leader of the study published recently by the group of Professor Tinnefeld. “We already knew that cellulosomes can bind their enzymes in two different orientations (dual binding mode), probably to increase the diversity of complexes that you can assembled with the same set of enzymes. What we have discovered now is that not all orientations are equally probable and that you can actually change the orientation using a second type of enzyme, a prolyl-isomerase”. These findings are important, since they mean that cellulosomes could change their 3D configuration in order to adapt to the heterogeneity of the lignocellulose material and maximize efficiency.

One question that remained opened was how cellulosomes change their enzyme composition in order to adapt to the changes of the substrates over time. According to Andrés Vera, “It was quite paradoxical. On one hand the cohesin-dockerin interaction, the molecular interaction that binds the enzymes to the cellulosome is extremely stable. But, on the other hand, we know that bacteria are able to change the composition of enzymes, how do they manage to do so if the binding is so strong?” The solution seems to be again in the regulation by prolyl-isomerases, as the researches showed that they can destabilize the cohesin-dockerin interaction.  “This can be a mechanism exploited by the microorganism to remodel their cellulosomes, but what is more exciting opens the doors to introduce this dynamic feature in artificial designer cellulosomes for the production of biofuels ”