DOE researhers use specialized optical microscope to see cellulase enzymes interacting with cellulose

In Pennsylvania, DOE researchers have used a specialized optical microscope to visualize single cellulase enzymes interacting with different forms of cellulose. By investigating enzyme function in the presence of the product of the reaction and other components of plant biomass, the researchers gained new insights into how the enzyme binds and processes cellulose.

The researchers found that the product of cellulose breakdown, cellobiose, can inhibit that breakdown process in two ways. It can bind to the “front door” of the enzyme where a cellulose strand threads into the enzyme. Alternately, it can bind to the “back door” of the enzyme where the product of the breakdown is discharged. This finding provides new avenues for developing modified enzymes that can tolerate working at high concentrations of cellobiose. Bioenergy researchers need enzymes with improved function to make biofuel more cost effective and reduce dependence on fossil fuels.

This study involved visualizing the model cellulase Cel7A using single-molecule fluorescence microscopy on a specialized “SCATTIRSTORM” microscope. By investigating the enzymes binding to and moving along the cellulose substrate one at a time, the researchers revealed enzyme behavior in much more detail than normal bulk studies. They found that the product of cellulose breakdown, cellobiose, slows the movement of Cel7A along cellulose, which was expected, but also that cellobiose blocks binding of Cel7A to cellulose, which was a surprise. This activity can be explained as a ‘front door’ inhibition, in which the cellobiose plugs the opening of a tunnel through the enzyme where the cellulose strand normally is threaded.