Structural basis for cellulose binding by the type A carbohydrate-binding module 64 of Spirochaeta thermophila (Proteins: Structure, Function, and Bioinformatics)

Spirochaeta thermophila secretes seven glycoside hydrolases for plant biomass degradation that carry a carbohydrate-binding module 64 (CBM64) appended at the C-terminus. CBM64 adsorbs to various ?1-4-linked pyranose substrates showing high affinity for cellulose. We present the first crystal structure of a CBM64 at 1.2 Å resolution, which reveals a jelly-roll-like fold corresponding to a surface-binding type A CBM. Modeling of its interaction with cellulose indicates that CBM64 achieves association with the hydrophobic face of ?-linked pyranose chains via a unique coplanar arrangement of four exposed tryptophan side chains. This article is protected by copyright. All rights reserved.