Structural and thermodynamic dissection of specific mannan recognition by a carbohydrate binding module, TmCBM27

Area of Science:

• Biochemistry
• Structural Biology
• Carbohydrate Chemistry

Background:

• Mannanases are enzymes that degrade mannans, important components of plant cell walls.
• Carbohydrate-binding modules (CBMs) are crucial for enzyme targeting and substrate recognition.
• CBM family 27 (CBM27) is known to interact with mannans, but its structural basis for specificity is not fully understood.

Purpose of the Study:

• To characterize the binding properties and specificity of the CBM27 domain from Thermotoga maritima mannanase (TmCBM27).
• To elucidate the structural basis for TmCBM27's recognition of mannooligosaccharides and branched mannans through X-ray crystallography.

Main Methods:

• Isolation and purification of the TmCBM27 domain.
• Binding assays to determine affinity for various polysaccharides (mannans, cellulose, xylan).
• X-ray crystallography to determine the structures of native TmCBM27 and its complexes with ligands.

Main Results:

• TmCBM27 exhibits high affinity for beta-1,4-mannooligosaccharides, carob galactomannan, and konjac glucomannan.
• TmCBM27 does not bind to cellulose or xylan, indicating high specificity.
• Crystal structures reveal the binding site architecture and how it accommodates mannooligosaccharides and branched galactomannans.

Conclusions:

• TmCBM27 is a specific mannan-binding CBM.
• The study provides the first structural insights into CBM recognition of branched plant cell wall polysaccharides.
• The binding site architecture dictates the specificity for mannans, including substituted variants.