Abstract
Upon investigation of Streptococcus pneumoniae serotype 15F capsular polysaccharide (CPS), we discovered that it had a different phosphorylation substituent, namely glycerol-2-phosphate like the other serogroup 15 CPS rather than the originally reported 0.2 equivalent of phosphate or phosphocholine. Furthermore, we also determined the locations of the two previously unassigned O-acetyl groups present in the repeating unit of the 15F CPS, and carried out full NMR assignments of the 15F as well as 15A CPS. Lastly, a biosynthetic analysis of serotypes 15F and 15A was performed and used to make a prediction for the structure of the recently discovered serotype 15D.
Highlights
Streptococcus pneumoniae is a major human pathogen, estimated as responsible for over one million deaths annually [1]
Upon investigation of Streptococcus pneumoniae serotype 15F capsular polysaccharide (CPS), we discovered that it had a different phosphorylation substituent, namely glycerol-2-phosphate like the other serogroup 15 CPS rather than the originally reported 0.2 equivalent of phosphate or phosphocholine
The sample still contained signals arising from one acetyl group as part of the CPS, which was identified as originating from a β-GlcpNAc
Summary
Streptococcus pneumoniae is a major human pathogen, estimated as responsible for over one million deaths annually [1]. It is a Gram posi tive bacterium encapsulated by a polysaccharide, known as capsular polysaccharide (CPS), which shields it from the host immune system. When 7D was first encountered several years ago, the strain that produced the CPS was initially identified as 7C using Quellung re action typing but as 7B using genetic analysis, and using NMR spec troscopy it was found to be a hybrid CPS with a 5:1 ratio between the CPS of 7C and 7B, arising when a 7B strain had a specific mutation at a crucial residue, F385L, in the glycosyltransferase wcwK producing a bispecific transferase [7]
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