ABSTRACT
We report the repeating unit structures of the native capsular polysaccharides of Streptococcus pneumoniae serotypes 41A and 41F. Structural determinations yielded six carbohydrate units in the doubly branched repeating unit to give the following structure for serotype 41A: The structure determinations were motivated (1) by an ambition to help close the remaining gaps in S. pneumoniae capsular polysaccharide structures, and (2) by the attempt to derive functional annotations of carbohydrate active enzymes in the biosynthesis of bacterial polysaccharides from the determined structures. An activity present in 41F but not 41A is identified as an acetyltransferase acting on the rhamnopyranosyl sidechain E. The genes encoding the formation of the six glycosidic bonds in serogroup 41 were determined from the capsular polysaccharide structures of serotype 41A, 41F, and genetically related serotypes, in conjunction with corresponding genomic information and computational homology searches. In combination with complementary information, NMR spectroscopy considerably simplifies the functional annotation of carbohydrate active enzymes in the biosynthesis of bacterial polysaccharides.
Subject(s)
Bacterial Capsules/chemistry , Polysaccharides, Bacterial/chemistry , Streptococcus pneumoniae/chemistry , Acetyltransferases/chemistry , Acetyltransferases/metabolism , Bacterial Capsules/genetics , Magnetic Resonance Spectroscopy , Molecular Structure , Polysaccharides, Bacterial/genetics , Serogroup , Streptococcus pneumoniae/genetics , Streptococcus pneumoniae/pathogenicityABSTRACT
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 is [formula: see text] and has identical composition to the capsular polysaccharide 10A, but two different linkages. The serotype 42 structure [formula: see text] closely resembles the genetically related serotype 35A, which does not contain residue A. The structure of the serotype 47F capsular polysaccharide [formula: see text] is 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.
Subject(s)
Bacterial Capsules/chemistry , Genome, Bacterial , Polysaccharides, Bacterial/chemistry , Streptococcus pneumoniae/chemistry , Bacterial Capsules/immunology , Carbohydrate Sequence , Cross Reactions , Epitopes/chemistry , Epitopes/immunology , Humans , Immune Sera/chemistry , Molecular Sequence Data , Multigene Family , Polysaccharides, Bacterial/immunology , Serogroup , Serotyping , Streptococcus pneumoniae/genetics , Streptococcus pneumoniae/immunologyABSTRACT
The structure of the serotype 47A (Danish nomenclature system) capsular polysaccharide from Streptococcus pneumoniae was elucidated by NMR spectroscopy. The following structure of the repeating heptasaccharide was deduced: [structure: see text]. The serotype 47A capsular polysaccharide is one of 91 structurally and serologically distinct capsular polysaccharides that have been recognized in S. pneumoniae, a significant human pathogenic bacterium and model system in medical microbiology. Structure and NMR spectra are compared to previously solved capsular polysaccharide structures of other serotypes.
