Structural Characterization of an Oligosaccharide Made by Neisseria sicca

Abstract

Neisseria sicca 4320 expresses two carbohydrate-containing components with sodium dodecyl sulfatepolyacrylamide gel electrophoresis mobilities that resemble those of lipooligosaccharide and lipopolysaccharide. Using matrix-assisted laser desorption ionization-time of flight and electrospray ionization mass spectrometry, we characterized a disaccharide carbohydrate repeating unit expressed by this strain. Commensal Neisseria strains colonize the human respiratory tract. Frequent interspecific genetic exchange between commensal Neisseria strains and the pathogens Neisseria meningitidis and Neisseria gonorrhoeae occurs (13). It is thought the commensal organisms serve as reservoirs for antibiotic resistance genes (20). The similarity between the gene complements of the commensals and pathogens suggests that the virulence of the pathogenic Neisseria spp. may not result from the genes that they possess but rather from a "genetic personality" which is a result of combinations of these genes, sequence variations that alter the function of gene products, the presence of genes for which a virulence phenotype has not yet been identified, and/or differences in the regulation of genes (25).Lipooligosaccharide (LOS) is an important neisserial virulence determinant consisting of an oligosaccharide (OS) component attached to lipid A via 3-deoxy-2-keto-D-manno-octulosonic acid (Kdo). The structures of a sufficient number of neisserial LOS molecules have been determined to form a coherent yet incomplete picture of the structural diversity of their LOS (Fig. 1). The different LOS structures have a conserved core with two Kdo molecules, two heptose (Hep) molecules, and one N-acetylhexosamine (HexNAc) molecule and vary in the composition and size of the OS attached to one Hep (HepI; ␣-chain variation) and in the attachment of an OS or phosphoethanolamine to the other Hep (HepII; ␤-chain variation) or by addition of a galactose to the Nacetylglucosamine (GlcNAc) found on HepII (␥-chain extension) (3, 6, 7, 9-11). This structural motif is different from that of lipopolysaccharide (LPS) of other types of bacteria, which contains an O antigen composed of a repeating sugar polymer, typically consisting of four to seven sugars (26). No one has reported the presence of an O antigen in pathogenic strains of Neisseria.A few studies have analyzed the structure of LOS produced by commensal Neisseria strains, and the data indicate that the LOS heterogeneity is greater than the heterogeneity in the gonococcus and meningococcus (21). Commensal Neisseria strains are capable of producing LOS molecules that are structurally different from the molecules in the known Neisseria repertoire in that they fail to bind monoclonal antibodies specific for LOS epitopes characteristic of the gonococcus and meningococcus (1). They also can lack some of the LOS biosynthesis genes found in N. meningitidis and N. gonorrhoeae (1,33). These findings suggest that alternative LOS structures are present in commensal Neisseria strains. Sandlin and Stein (21) identified ...

Sequence-Based Predictions of Lipooligosaccharide Diversity in the Neisseriaceae and Their Implication in Pathogenicity

“…This would indicate that LOS isolated from commensal and pathogenic Neisseria strains should all possess two KDO residues. This is supported by all structural data on neisserial LOSs, which indicate that they all possess two KDO residues [7] , [44] , [45] , [46] , [47] , [48] , [49] .…”

“…The predicted structure of N. sicca 4320 core LOS contains three heptose residues [49] . Therefore, we searched the neisserial genomes using the E. coli DH1 heptosyl transferase III amino acid sequence.…”

“… The structure of LOS presented in this figure is a composite derived from several published structures of neisserial LOS [5] , [6] , [8] , [15] , [28] , [30] , [44] , [49] , [59] , [60] , [61] . …”

Analysis of Bacterial Lipooligosaccharides by MALDI-TOF MS with Traveling Wave Ion Mobility

“…Although they usually contain only one repeat unit, SR-type LPS may contain two O-antigen subunits where the reducing termini of the subunits have different anomeric configurations [60]. A dHex moiety, rhamnose, was recently reported as a constituent of the LPS of another commensal species of Neisseria, N. sicca [61]. Further detailed analyses of the LOS/LPS from N. flavescens 4322 are required in order to identify monosaccharide constituents and confirm the proposed composition of the O-antigen.…”