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Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
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Capsular polysaccharide conformations in pneumococcal serotypes 19F and 19A
Michelle M Kuttel1, Graham E Jackson2, Mpho Mafata2
1Department of Computer Science, University of Cape Town, Cape Town, South Africa.
Carbohydrate Research
|February 7, 2015
Summary
Pneumococcal conjugate vaccines (PCV) have reduced disease, but serotype 19A infections increased. Structural differences between 19F and 19A polysaccharides explain the lack of cross-protection, guiding future vaccine development.
Area of Science:
- Microbiology
- Immunology
- Structural Biology
Background:
- Streptococcus pneumoniae causes significant childhood illness.
- Pneumococcal conjugate vaccines (PCV7) reduced disease but increased non-vaccine serotype 19A infections.
- Cross-protection from vaccine serotype 19F to 19A was expected but not observed.
Purpose of the Study:
- To investigate the structural basis for the lack of cross-protection between Streptococcus pneumoniae serotypes 19F and 19A.
- To compare the conformational properties of 19F and 19A oligosaccharide chains.
Main Methods:
- Solution simulations of 19F and 19A oligosaccharide chains.
- Nuclear Magnetic Resonance (NMR) NOESY experiments to determine inter-residue distances.
Main Results:
- Both 19F and 19A polysaccharides form unstructured random coils.
- Distinct conformational differences were identified: 19F has residues in near-orthogonal orientations, while 19A has residues in similar orientations.
- 19F favors extended conformations, whereas 19A shows a high prevalence of tight hairpin bends.
Conclusions:
- Conformational differences between 19F and 19A polysaccharides likely explain the absence of antibody cross-protection.
- These findings are crucial for understanding pneumococcal serotype epidemiology and for designing next-generation pneumococcal vaccines like PCV13.
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