Abstract
Glycoside hydrolases (GHs) play fundamental roles in the decomposition of lignocellulosic biomaterials. Here, we report the full-length structure of a cellulase from Bacillus licheniformis (BlCel5B), a member of the GH5 subfamily 4 that is entirely dependent on its two ancillary modules (Ig-like module and CBM46) for catalytic activity. Using X-ray crystallography, small-angle X-ray scattering and molecular dynamics simulations, we propose that the C-terminal CBM46 caps the distal N-terminal catalytic domain (CD) to establish a fully functional active site via a combination of large-scale multidomain conformational selection and induced-fit mechanisms. The Ig-like module is pivoting the packing and unpacking motions of CBM46 relative to CD in the assembly of the binding subsite. This is the first example of a multidomain GH relying on large amplitude motions of the CBM46 for assembly of the catalytically competent form of the enzyme.
Highlights
Glycoside hydrolases (GHs) play fundamental roles in the decomposition of lignocellulosic biomaterials
To other members of the GH5 family, the catalytic domain (CD) of BlCel5B has a typical TIM barrel fold with eight inner β -strands and eight outer α helices that are interconnected by loops and three short α helices
The distance between the α carbons of two residues centrally positioned in the CD and CBM46 (Fig. 4A) was monitored, and the results shown in Fig. 4B indicate that the wide-amplitude events described above frequently appear in this time scale
Summary
Glycoside hydrolases (GHs) play fundamental roles in the decomposition of lignocellulosic biomaterials. The Ig-like module is pivoting the packing and unpacking motions of CBM46 relative to CD in the assembly of the binding subsite. This is the first example of a multidomain GH relying on large amplitude motions of the CBM46 for assembly of the catalytically competent form of the enzyme. The molecular architecture of glycoside hydrolases (GHs) frequently consists of a catalytic domain (CD), where hydrolysis occurs, and one or more ancillary modules (AMs), which are usually connected by less structured linkers. CBMs enhance the accessibility of CDs to carbohydrate chains to improve enzymatic activity, making them important candidates for the development of effective biomass-degrading enzymes in industrial settings. CBMs were shown to extend and complement the CD substrate-binding site in www.nature.com/scientificreports/
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