Structural elucidation of two capsular polysaccharides from one strain of Bacteroides fragilis using high-resolution NMR spectroscopy

Abstract

The capsule of Bacteroides fragilis is unusual in that it consists of two distinct capsular polysaccharides. Using a combination of high-resolution NMR spectroscopy, theoretical calculations, and as few chemical procedures as required, the structure of both polysaccharide antigens (polysaccharides A and B) was elucidated. Using the above procedures, it was possible to obtain the complete structures using minimal quantities of polysaccharides A and B (8 and 5 mg, respectively). Only small amounts of each subjected to chemical analysis were not recoverable. Polysaccharide A is composed of the following repeating unit: [----3)alpha-D-AATp(1----4)[beta-D-Galf(1----3)]alpha-D- GalpNAc(1----3)beta-D-Galp(1----], where AAT is 2-acetamido-4-amino-2,4,6-trideoxygalactose. A pyruvate substituent having the R configuration spans O-4 and O-6 of the beta-D-galactopyranosyl residue. Polysaccharide B is composed of the following repeating unit: [----4)alpha-L-QuipNAc(1----3)beta-D-QuipNAc(1----4)[alpha-L - Fucp(1----2)beta-D-GalpA(1----3)beta-D-GlcpNAc(1----3)]alpha -D-Galp(1----]. A 2-aminoethylphosphonate substituent is situated on O-4 of the N-acetyl-beta-D-glucopyranosyl residue.

UDP-galactofuranose Precursor Required for Formation of the Lipopolysaccharide O Antigen of Klebsiella pneumoniae Serotype O1 Is Synthesized by the Product of the rfbDKPO1 Gene

“…The 31 P spectrum of 4000 scans was recorded without proton decoupling. The two-dimensional homonuclear magnitude COSY, phase-sensitive TOCSY, 1 H-31 P HMQC, 1 H- 13 C HMQC experiments were recorded and processed as described previously (56). The one-dimensional TOCSY z-filtered spectra of 2000 scans was performed as described previously (57).…”

Bacteroides: the Good, the Bad, and the Nitty-Gritty

“…Two distinct high-molecular-weight polysaccharides (PS-A and PS-B) that are coexpressed were described (179,283), and the structures of these two polysaccharides were elucidated (14). PS-A is made up of repeating tetrasaccharide units, and PS-B is made up of repeating hexasaccharide units (283,289).…”

Role of glycan synthesis in colonization of the mammalian gut by the bacterial symbiont Bacteroides fragilis

“…Such genes often are located outside the polysaccharide biosynthesis loci in conserved areas of the genome to ensure that synthesis of a polysaccharide is not dependent on a product encoded by another phase-variable locus (5). The structures of B. fragilis 9343 polysaccharide A (PSA) and PSB are known (10), and both contain complex diand tri-deoxy monosaccharides: PSA contains 2-acetamido-4-amino-2,4,6-trideoxy-D-galactose (AATGal), and PSB contains D-and L-N-acetylquinovosamine (D-and L-QuiNAc). The synthesis of such sugars should first require conversion of UDP-Nacetylglucosamine (UDP-GlcNAc) to a UDP-2-acetamido-4-keto-2,4,6-trideoxy-D-glucose intermediate by a UDP-GlcNAc 4,6-dehydratase [supporting information (SI) Fig.…”