Supercomputer targets cellulose bottleneck

Producing ethanol from cellulose is slow and expensive, the central bottleneck being the sluggish rate at which the cellulose enzyme complex breaks down tightly bound cellulose into sugars.

To help unlock the cellulose bottleneck, a team of scientists has conducted molecular simulations at the San Diego Supercomputer Centre (SDSC), based at UC San Diego. By using ‘virtual molecules,’ they have discovered key steps in the intricate dance in which the enzyme acts as a molecular machine. They attach to bundles of cellulose, pull up a single strand of sugar, and put it onto a molecular ‘conveyor belt’ where it is chopped into smaller sugar pieces.

In their simulations, the scientists found that initially the binding part of the enzyme moves freely and randomly across the cellulose surface, searching for a broken cellulose chain. When it encounters an available chain, the cellulose itself seems to prompt a change in the shape of the enzyme complex so that it can straddle the broken end of the cellulose chain. This gives the enzyme a crucial foothold to begin the process of digesting or ‘unzipping’ the cellulose into sugar molecules.