Bacterial periplasmic sialic acid-binding proteins exhibit a conserved binding site

Area of Science:

• Microbiology and Structural Biology
• Bacterial Pathogenesis
• Biochemistry

Background:

• Sialic acids are vital nine-carbon sugar acids in eukaryotes and prokaryotes.
• Pathogenic bacteria utilize sialic acids for immune evasion and molecular mimicry.
• Sialic acid transport into bacterial cytoplasm often involves tripartite ATP-independent systems.

Purpose of the Study:

• To structurally and thermodynamically characterize periplasmic sialic acid-binding proteins from pathogenic bacteria.
• To investigate the impact of mutations on sialic acid binding affinity.
• To elucidate the conserved binding mechanisms and conformational changes involved in sugar recognition.

Main Methods:

• X-ray crystallography for structural characterization of periplasmic binding proteins.
• Isothermal titration calorimetry for thermodynamic characterization of sugar binding.
• Site-directed mutagenesis to analyze binding site alterations.

Main Results:

• Structural and thermodynamic data were obtained for proteins from Fusobacterium nucleatum, Pasteurella multocida, and Vibrio cholerae.
• Conserved binding pockets and similar binding affinities were observed across these bacterial species.
• Significant conformational changes upon sugar binding were identified, with the C1 carboxylate as the primary binding site.

Conclusions:

• Bacterial sialic acid-binding proteins share conserved structural features and binding mechanisms.
• A conserved hydrogen-bonding network stabilizes the sugar-bound conformational state.
• Understanding these mechanisms is key to targeting bacterial nutrient acquisition and pathogenesis.