Determination of native capsular polysaccharide structures of Streptococcus pneumoniae serotypes 39, 42, and 47F and comparison to genetically or serologically related strains

• Structures were obtained for serotype 39, 42, and 47F capsular polysaccharides.
• Serotype 39 polysaccharide differs from 10A in two linkages.
• Serotype 42 has close structural resemblance to 35A, but contains a branch.
• Serotype 47F contains a structural motif resembling serotype 35A and 42.
• The resemblance explains the reaction of typing serum 35a with serotype 47F.

The diversity of capsular polysaccharides of the bacterial pathogen Streptococcus pneumoniae leads to at least 91 different serotypes. While the genetic loci for capsular biosynthesis have been characterized for all serotypes, the determination of resultant polysaccharide structures remains incomplete. Here, we report the chemical structures of the capsular polysaccharides of serotypes 39, 42, and 47F from the genetic cluster 4, and discuss the structures in the context of structures from serologically and genetically related serotypes. Antigenic determinants can be approximated in this manner.The structure of the serotype 39 capsular polysaccharide isFigure optionsDownload as PowerPoint slideand has identical composition to the capsular polysaccharide 10A, but two different linkages.The serotype 42 structureFigure optionsDownload as PowerPoint slideclosely resembles the genetically related serotype 35A, which does not contain residue A.The structure of the serotype 47F capsular polysaccharideFigure optionsDownload as PowerPoint slideis somewhat different from a recently determined structure from the same serogroup, while containing a structural motif that is reflected in serotype 35A and 42 capsular polysaccharide structures, thus explaining the cross-reactivity of serotype 47F with the typing serum 35a.

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