Expansins are disruptive proteins that loosen growing plant cell walls and can enhance the enzymatic hydrolysis of cellulose when mixed with cellulases. The canonical expansin structure consists of one domain responsible for substrate binding (D2) and another domain (D1) of unknown function, but essential for activity. Although the effects of expansins on cell walls and cellulose fibrils are known, the molecular mechanism underlying their biophysical function is poorly understood. Using computational molecular dynamics simulations, CCES scientists
show that BsEXLX1 can slide on the hydrophobic surface of crystalline cellulose via the flat aromatic surface of its binding domain D2, and that BsEXLX1 can hydrogen bond a free glucan chain in a twisted conformation through the domain D1. These results suggest that BsEXLX1 could move on the surface of cellulose and disrupt hydrogen bonds by twisting glucan chains. This process weakens the cell wall structure so that enzymes can attack it more efficiently to produce biofuels, for example.
