Identification of a novel heptoglycan of alpha1-->2-linked D-glycero-D-manno-heptopyranose. Chemical and antigenic structure of lipopolysaccharides from Klebsiella pneumoniae ssp. pneumoniae rough strain R20 (O1-:K20-).

In a preliminary investigation (Süsskind, M., Müller-Loennies, S., Nimmich, W., Brade, H., and Holst, O. (1995) Carbohydr. Res. 269, C1-C7), we identified after deacylation of lipopolysaccharides (LPS) from Klebsiella pneumoniae ssp. pneumoniae rough strain R20 (O1(-):K20(-)) as a major fraction the oligosaccharide,-structure; see text- where Kdo was 3-deoxy-D-manno-oct-2-ulopyranosonic acid and Hepp was manno-heptopyranose. The presence of the threo-hex-4-enuronopyranosyl residue indicated a substituent at O-4 of the second GalA residue linked to O-3 of the second L,D-Hep residue, which had been eliminated by treatment with hot alkali. We now report the complete structure of lipopolysaccharide, which was elucidated by additional characterization of isolated core oligosaccharides and analysis of the lipid A. The substituent at O-4 of the second GalpA is D-GlcpN, which in a fraction of the LPS is substituted at O-6 by three or four residues of D-glycero-D-manno-heptopyranose (D,D-Hepp). The complete carbohydrate backbone of the LPS is as follows, -structure; see text- (L-glycero-D-manno-heptopyranose; L,D-Hepp), where all hexoses possess the D-configuration. Sugars marked with an asterisk are present in nonstoichiometric amounts. The structure is unique with regard to the presence of an alpha1-->2-linked D-glycero-D-manno-heptoglycan (oligosaccharide), which has not been described to date, and does not contain phosphate substituents in the core region. Fatty acid analysis of lipid A identified (R)-3-hydroxytetradecanoic acid as sole amide-linked fatty acid and (R)-3-hydroxytetradecanoic acid, tetradecanoic acid, small amounts of 2-hydroxytetradecanoic acid, hexadecanoic acid, and traces of dodecanoic acid as ester-linked fatty acids, substituting the carbohydrate backbone D-GlcpN4Pbeta1-->6D-GlcpNalpha1P. The nonreducing GlcN carries four fatty acids, present as two 3-O-tetradecanoyltetradecanoic acid residues, one of which is amide-linked and the other ester-linked to O-3'. The reducing GlcN is substituted in a nature fraction of lipid A by two residues of (R)-3-hydroxytetradecanoic acid, one in amide and the other in ester linkage at O-3. Two minor fractions of lipid A were identified; in one, the amide-linked (R)-3-hydroxytetradecanoic acid at the reducing GlcN is esterified with hexadecanoic acid, resulting in 3-O-hexadecanoyltetradecanoic acid, and in the second, one of the 3-O-tetradecanoyltetradecanoic acid residues at the nonreducing GlcN is replaced by 3-O-dodecanoyltetradecanoic acid. Thus, the complete structure of LPS is as shown in Fig. 1. After immunization of BALB/c mice, two monoclonal antibodies were obtained that were shown to be specific for the core of LPS from K. pneumoniae ssp. pneumoniae, since they did not react with LPS or whole-cell lysates of a variety of other Gram-negative species. Both monoclonal antibodies could be inhibited by LPS but not by isolated oligosaccharides and are thus considered to recognize a conformational epitope in the core region.