Stability and Ligand Promiscuity of Type A Carbohydrate-binding Modules Are Illustrated by the Structure of Spirochaeta thermophila StCBM64CDeconstruction of cellulose, the most abundant plant cell wall polysaccharide, requires the cooperative activity of a large repertoire of microbial enzymes. Modular cellulases contain non-catalytic type A carbohydrate-binding modules (CBMs) that specifically bind to the crystalline regions of cellulose, thus promoting enzyme efficacy through proximity and targeting effects. Although type A CBMs play a critical role in cellulose recycling, their mechanism of action remains poorly understood. Here we produced a library of recombinant CBMs representative of the known diversity of type A modules.
The Mechanism by Which Arabinoxylanases Can Recognize Highly Decorated XylansThe enzymatic degradation of plant cell walls is an important biological process of increasing environmental and industrial significance. Xylan, a major component of the plant cell wall, consists of a backbone of β-1,4-xylose (Xylp) units that are often decorated with arabinofuranose (Araf) side chains. A large penta-modular enzyme, CtXyl5A, was shown previously to specifically target arabinoxylans. The mechanism of substrate recognition displayed by the enzyme, however, remains unclear. Here we report the crystal structure of the arabinoxylanase and the enzyme in complex with ligands.
Combined Crystal Structure of a Type I Cohesin: MUTATION AND AFFINITY BINDING STUDIES REVEAL STRUCTURAL DETERMINANTS OF COHESIN-DOCKERIN SPECIFICITIESBackground: Cellulosomal cohesin-dockerin types are reversed in Bacteroides cellulosolvens.Results: Combined crystallographic and computational approaches of a lone cohesin yielded a structural model of the cohesin-dockerin complex that was verified experimentally.Conclusion: The dockerin dual-binding mode is not exclusive to enzyme integration into cellulosomes; it also characterizes cell-surface attachment.Significance: This combined approach provides a platform for generating testable hypotheses of the high affinity cohesin-dockerin interaction.