Phosphate localization in carbohydrates - a study on enterobacterial lipopolysaccharides

Area of Science:

• Carbohydrate Chemistry
• Bacterial Lipopolysaccharides
• Structural Analysis

Background:

• Phosphate substituent localization in Enterobacteriaceae lipopolysaccharides was previously limited to Salmonella minnesota and Escherichia coli B.
• Existing methods relied on beta-elimination reactions after periodate oxidation.

Purpose of the Study:

• To develop a generally applicable method for determining phosphate group localization and substitution extent in carbohydrates.
• To apply this method to core oligosaccharides from specific E. coli and P. mirabilis strains.

Main Methods:

• A novel reaction sequence: methylation, dephosphorylation, and reetherification (labeling) with ethyl iodide.
• Derivatization to partially methylated alditol acetates.
• Analysis using combined gas chromatography/mass spectrometry.

Main Results:

• Phosphate groups were localized at C-4 of chain heptoses in E. coli C and E. coli R4 lipopolysaccharides.
• Phosphate was found at C-7 of the branching heptose in P. mirabilis R4/O 28 lipopolysaccharide.
• The method was successfully applied to core oligosaccharides from E. coli C23.1, E. coli C71, E. coli F2515, and P. mirabilis R4/O 28.

Conclusions:

• The developed method provides a robust approach for mapping phosphate substituents in complex carbohydrates.
• This technique advances the structural understanding of lipopolysaccharides in various bacterial species.
• Accurate localization of phosphate groups is crucial for understanding bacterial cell wall structure and function.