A polysaccharide utilization locus from the gut bacterium Dysgonomonas mossii encodes functionally distinct...

Area of Science:

• Microbiology
• Biochemistry
• Enzymology

Background:

• The gut microbiota is vital for human health, degrading dietary fiber into beneficial short-chain fatty acids.
• Xylan, a major dietary fiber component, requires carbohydrate esterases (CEs) to remove hindering decorations for efficient breakdown by glycoside hydrolases (GHs).
• CE families 1 and 6 (CE1, CE6) are key in xylan degradation, but their functional diversity remains underexplored, particularly in dominant gut bacteria like Bacteroidetes.

Purpose of the Study:

• To characterize novel carbohydrate esterases (CEs) from a polysaccharide utilization locus (PUL) in the gut Bacteroidete Dysgonomonas mossii.
• To investigate the functional diversity and distinct activities of CE1 and CE6 enzymes involved in xylan degradation.
• To elucidate the structural basis of CE activity and substrate interaction within the gut environment.

Main Methods:

• Enzyme characterization of three CEs from a Dysgonomonas mossii PUL.
• Assays to determine acetyl esterase and feruloyl esterase activities.
• Structural analysis, including X-ray crystallography, of CE domains and their complexes with ligands.

Main Results:

• Identified three functionally distinct CEs: one highly active CE6 acetyl esterase and two CE1 feruloyl esterases.
• Characterized a multidomain CE1 enzyme with distinct N-terminal (active feruloyl esterase) and C-terminal (low activity) CE1 domains.
• Determined the crystal structure of the C-terminal CE1 domain, revealing a linked carbohydrate-binding module, and its complex with methyl ferulate.

Conclusions:

• Dysgonomonas mossii invests in multiple CEs, indicating the importance of efficient xylan de-decoration for nutrient release in the gut.
• The distinct functional roles of these CEs highlight the complexity of polysaccharide degradation in the gut microbiota.
• Structural insights provide a basis for understanding CE mechanism and potential engineering for improved biomass conversion.