Full NMR assignment and revised structure for the capsular polysaccharide from Streptococcus pneumoniae type 15B

Area of Science:

• Carbohydrate Chemistry
• Structural Biology
• Vaccine Development

Background:

• Streptococcus pneumoniae Type 15B capsular polysaccharide is a key component of the 23-valent pneumococcal polysaccharide vaccine.
• Understanding the precise chemical structure of bacterial polysaccharides is vital for vaccine efficacy and safety.

Purpose of the Study:

• To elucidate the complete structure of the Streptococcus pneumoniae Type 15B capsular polysaccharide.
• To identify the specific phosphorylated substituent and its location.
• To characterize the O-acetylation pattern of the polysaccharide.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was employed for full structural assignments.
• Analysis of both native and de-O-acetylated polysaccharide forms.
• Chemical characterization of substituent groups and their positions.

Main Results:

• Full NMR assignments were obtained for the native and de-O-acetylated polysaccharide.
• The phosphorylated substituent was confirmed as glycerol-2-phosphate, located on the O-3 of the beta-Galp residue.
• O-acetylation was identified on the terminal alpha-Gal residue, with specific distribution across hydroxyl groups (O-2, O-3, O-4, O-6).

Conclusions:

• The structural characterization clarifies the composition of the Streptococcus pneumoniae Type 15B polysaccharide.
• The identification of glycerol-2-phosphate provides critical information for vaccine design and understanding immune response.
• The detailed O-acetylation pattern offers insights into polysaccharide stability and antigenicity.