Structural Relationships and Sialylation among Meningococcal L1, L8, and L3,7 Lipooligosaccharide Serotypes

Abstract

Eighteen of 34 endemic meningococcal case strains were of the L8 lipooligosaccharide (LOS) type; four of these were both L3 and L7 (L3,7), and seven were L1. L1 structures arose by alternative terminal Gal substitutions of lactosyl diheptoside L8 structures, as determined by electrospray ionization and other mass spectrometric techniques, and enzymatic and chemical degradations (Structures L1 and L1a).(NeuNAc␣2) 3 Gal␣1 3 4Gal␤1 3 4Glc␤1 3 4Hep␣1 3 (Kdo) 2 1Gal␣1 3 4GlcNAc(OAc)␣1 3 2Hep3 4 (PEA) STRUCTURE L1aThe more abundant molecule, designated L1, had a trihexose globosyl ␣ chain; the less abundant one, designated L1a, had a ␤-lactosyl ␣ chain and a parallel ␣-lactosaminyl ␥ chain. A P k globoside (Gal␣134Gal␤134 Glc-R) monoclonal antibody bound 9/10 L1 strains, but a P 1 globoside (Gal␣134Gal␤134GlcNAc-R) mAb bound none of them. ␣-Galactosidase caused loss of both L1 structures and creation of L8 structures; ␤-galactosidase caused loss of the L8 determinant. The L1/P k glycose was partially sialylated. Some LOS also had unsubstituted basal ␤-GlcNAc additions. These structural relationships explain co-expression of L8, L1, and L3,7 serotypes. The outer membrane lipooligosaccharides (LOS)1 of Neisseria meningitidis have been divided into 11 serotypes (1), but this system of antigenic discrimination does not adequately account for the observed molecular heterogeneity of these glycolipids (2-5) nor for the fact that the several different LOS molecules made by each meningococcus may be of different serotypes. Monoclonal antibodies (mAbs) largely have replaced rabbit antisera as the LOS typing reagent (6, 7), but a set of mAbs that recognizes most of the important LOS antigens is not available, and many of the available mAbs lack a complete structural definition of their cognate epitopes (8 -10). Furthermore, mAb LOS typing has been applied mostly to epidemiologically related strains (6, 7), which may have introduced biases that have led to underestimates of the prevalences of some LOS types among circulating organisms. For these reasons we have used a variety of mass spectrometric and standard immunochemical techniques to investigate the structural basis of LOS serotype heterogeneity and mAb binding among meningococci that caused sporadic disease. We began with the L1, L8, and L3,7 types.Neisseria LOS structurally resemble human glycosphingolipids (GSL) which often are sialylated (2, 11, 12). Group B and C N. meningitidis endogenously sialylate lacto-N-neotetraose LOS structures (13-15). We now report that the ␣ chain of the L1 LOS that mimics the human P k globosyl GSL also is partially sialylated and that L1 strains make a second, alternative LOS structure that we have designated L1a. Whether the L1a structure also is sialylated was not determined. EXPERIMENTAL PROCEDURESStrains-We have extensively characterized N. meningitidis strains 6940 (B:L1) the prototype L1 strain (16), and 126E (C:L1,8) (5,17,18), and 190I (B:L1,3,7) (19). We selected Neisseria lactamica strain 1207-0 and N. meningitidis strains 8529 (B...

Biochemical Analysis of Lpt3, a Protein Responsible forPhosphoethanolamine Addition to Lipooligosaccharide ofPathogenic Neisseria

“…The absence of PEA at 3-C of HepII (3-HepII) also results in the loss of MAb 2-1-L8 binding. This loss was demonstrated by an oligosaccharide with a L8 epitope composition (Hex) 2 (Hep) 2 (HexNAc) 1 (PEA) 1 (KDO) 2 failing to bind the MAb 2-1-L8 when PEA was absent from 3-HepII (11).…”

“…1. This antibody binds the 3.6-kDa LOS resulting when LgtE is expressed, and when LgtA, LgtG, and LgtC are not produced (11). MAb 2-1-L8 loses its affinity for LOS if LgtA, LgtC, or LgtG is expressed (4,6,7,33).…”

Importance of Antibodies to Lipopolysaccharide in Natural and Vaccine-Induced Serum Bactericidal Activity against Neisseria meningitidis Group B

“…Three immunotypes (L9, L10, and L11) were associated mostly with serogroup A strains, and the other eight were associated with all other serogroups. These immunotypes were subsequently confirmed by structural analysis of the respective oligosaccharides (9,16,20,24,29,37,38,42). Since that time, it has become evident that additional variations in structure, not identified by the initial immunotyping scheme, such as the substitution of glycine at the 7 position of Hep II, occur among N. meningitidis strains (25,44).…”

Structural and Immunochemical Characterization of the Lipooligosaccharides Expressed byNeisseria subflava44

“…The ␥ chain has been found in all strains examined and consists of a GlcNAc or GlcNAc (acetate) linked to Hep II. Occasionally, this chain is elongated by the addition of galactose (15). Some positions of Hep I and Hep II are also available for phosphoethanolamine (PEA) or phosphate addition (10,29).…”

“…Gonococcal and meningococcal LOSs have been examined by chemical (11,18,22), biological (17), and immunological techniques (28,42), as well as through visualization by silver staining sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gels (26,43). LOS is an amphipathic molecule that consists of a hydrophilic carbohydrate moiety attached to a hydrophobic lipid A moiety through two molecules of the acidic sugar 3-deoxy-D-manno-2-octulosonic acid (KDO).…”