Molecular plasticity of CBM3 ancillary domain leads to conformational changes in the cellulose binding interface

Carbohydrate-binding modules (CBMs) constitute independently folded domains typically associated with carbohydrate-active enzymes (CAZymes). These modules are considered to have a rigid structure without notable conformational changes upon ligand binding, exhibiting a complementary topography in relation to the target carbohydrate. Herein, the high-resolution SAD-solved structure of a CBM from family 3 (BsCBM3) that binds to crystalline cellulose is reported in two crystalline forms. This module showed molecular plasticity with structural differences detected between the two crystalline forms and high RMSD values when compared to NMR ensemble of models. Pronounced structural variances were observed in the cellulose binding interface between NMR and XTAL structures, which were corroborated by molecular dynamics simulations. These findings support that family 3 CBMs targeting to cellulose are rather structurally dynamic modules than rigid entities, suggesting a potential role of conformational changes in polysaccharide recognition and modulation of enzyme activity. (c) 2023 Elsevier Inc. All rights reserved.

Automated summary

Carbohydrate-binding modules (CBMs) are independently folded domains associated with carbohydrate-active enzymes (CAZymes). The high-resolution SAD-solved structure of a CBM from family 3 (BsCBM3) that binds to crystalline cellulose is reported, showing molecular plasticity and structural differences between crystalline forms. Variations in the cellulose binding interface were observed, supporting the idea that family 3 CBMs are structurally dynamic and suggesting a role in polysaccharide recognition and enzyme activity modulation.