Comparative Molecular Dynamics Study of Cellulose I-Beta and III(I) Allomorphs

Recent experiments show that when cellulose I-beta is converted into cellulose III(I) (via liquid NH3 pretreatment) the enzymatic hydrolysis rate increases 2-5 times. Interestingly the same experimental studies show a reduced non--specific enzyme binding for cellulose III(I) respect to cellulose I-beta.

Motivated by these experimental findings, we present the first comparative, long--time (200 ns) molecular dynamics study on the cellulose I-beta and III(I) allomorphs. The main purpose of our extensive computational study is to gain a detailed understanding of the relative differences between the two cellulose allomorphs in terms of structural, thermal and solvation properties and to relate those differences to enzyme binding and digestibility.

Our simulations reveal that the thermal fluctuations along both the intersheet and the intrasheet directions within the cellulose fibrils are larger in cellulose III(I) respect to cellulose I-beta and that the extent of the water--cellulose hydrogen bond network (hydration) was larger in cellulose III(I) than in cellulose I-beta. We will show how these results can provide a detailed physico-chemical description of the differences between cellulose I-beta and cellulose III(I) in terms of both enzyme binding and activity.