Carbohydrate Deacetylase Unique to Gut Microbe Bacteroides Reveals Atypical Structure

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Bacteroides, particularly Bacteroides ovatus, are abundant gut commensals linked to both health benefits and autoimmune disorders like IBD.
• Bacterial capsular polysaccharides (CPS) are key in host interactions, but their biosynthesis in Bacteroides is not fully understood.
• Understanding CPS biosynthesis is crucial for modulating host-microbe interactions in the gut.

Purpose of the Study:

• To structurally and functionally characterize a putative polysaccharide deacetylase (BoPDA) from Bacteroides ovatus.
• To elucidate the unique structural features and catalytic mechanism of BoPDA involved in CPS biosynthesis.
• To provide the first detailed characterization of a CPS biosynthesis protein from Bacteroides ovatus.

Main Methods:

• High-resolution crystal structures of BoPDA were solved with various divalent cations (Co2+, Ni2+, Cu2+, Zn2+).
• Carbohydrate binding and deacetylase activity assays were performed.
• Structural analysis focused on domain architecture and metal-binding motifs.

Main Results:

• BoPDA exhibits an atypical domain architecture with a CE4 catalytic domain inserted into a CBM.
• The enzyme utilizes a noncanonical His-Asp dyad for metal ion binding, differing from the typical CE4 motif.
• Crystal structures revealed enzyme-cation interactions at high resolution (1.36-1.56 Å).

Conclusions:

• BoPDA is the first characterized protein involved in CPS biosynthesis from Bacteroides ovatus.
• The unique structural and catalytic features of BoPDA advance our understanding of CPS biosynthesis in this medically relevant gut microbe.
• This work provides a foundation for future studies on the role of CPS in Bacteroides-host interactions.