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Xyloglucan is recognized by carbohydrate-binding modules that interact with beta-glucan chains
Shabir Najmudin1, Catarina I P D Guerreiro, Ana L Carvalho
1Requimte, Departamento de Química, FCT-UNL, 2829-516 Caparica, Portugal, CIISA-Faculdade de Medicina Veterinária, Universidade Técnica de Lisboa, Avenida da Universidade Técnica, 1300-477 Lisboa, Portugal.
The Journal of Biological Chemistry
|November 30, 2005
Summary
Researchers discovered a novel carbohydrate-binding module (CBM44) that binds to both cellulose and xyloglucan, crucial plant cell wall components. This finding advances our understanding of plant cell wall degradation mechanisms.
Area of Science:
- Biochemistry
- Plant Biology
- Structural Biology
Background:
- Enzyme systems targeting plant cell walls utilize carbohydrate-binding modules (CBMs) for attachment.
- Xyloglucan is a major plant cell wall polysaccharide, but specific CBMs binding to it were previously unidentified.
Purpose of the Study:
- To identify and characterize novel CBMs that bind to xyloglucan.
- To elucidate the structural basis for CBM recognition of decorated polysaccharides.
Main Methods:
- Protein expression and purification of CtCel9D-Cel44A.
- Crystallography to determine the structures of CBM44 and CBM30.
- Mutagenesis studies to investigate ligand-binding interactions.
Main Results:
- A novel CBM, CBM44, was identified within CtCel9D-Cel44A, exhibiting equal affinity for cellulose and xyloglucan.
- Crystal structures revealed a beta-sandwich fold with a hydrophobic platform accommodating glucose residues, crucial for ligand binding.
- Mutagenesis confirmed the role of the hydrophobic platform in ligand recognition, with polar residues playing a minor role.
Conclusions:
- CBM44 represents a novel class of CBMs capable of binding decorated polysaccharides like xyloglucan.
- The hydrophobic platform is a key feature for recognizing both linear and decorated beta-1,4-glucans.
- This work provides structural insights into the mechanism of plant cell wall polysaccharide recognition by CBMs.