Structural insights into WcbI, a novel polysaccharide-biosynthesis enzyme

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• Capsular polysaccharides (CPSs) are vital protective structures for Gram-negative bacteria, including the pathogen Burkholderia pseudomallei.
• The CPS of B. pseudomallei is critical for its virulence and a potential target for novel therapeutics.
• The wcbI gene is essential for CPS biosynthesis, but its function and structure were previously unknown.

Purpose of the Study:

• To determine the crystal structure of the WcbI protein from B. pseudomallei.
• To elucidate the function of WcbI in the context of capsular polysaccharide biosynthesis.
• To identify potential therapeutic targets based on WcbI's structure and function.

Main Methods:

• X-ray crystallography at 1.38 Å resolution using halide-soak multiple anomalous dispersion.
• Co-crystallization of WcbI with its proposed product, coenzyme A (CoA).
• Structural analysis, biophysical assays, and biochemical tests to assess enzyme activity.

Main Results:

• The crystal structure of WcbI bound to CoA was determined, revealing a novel helical fold with a CoA-binding pocket.
• Structural and biophysical data suggest WcbI functions as an acetyltransferase.
• Biochemical assays indicate that WcbI may require an additional functional module for mature capsule formation.

Conclusions:

• WcbI is a novel acetyltransferase involved in B. pseudomallei capsular polysaccharide biosynthesis.
• The determined structure provides insights into the mechanism of capsule formation and potential drug targeting.
• Further research is needed to identify the accessory factors involved in WcbI-mediated acetylation for complete capsule maturation.