The structure of the lipooligosaccharide (LOS) from the (alpha-1,2-N-acetyl glucosamine transferase (rfaK(NMB)) mutant strain CMK1 of Neisseria meningitidis: implications for LOS inner core assembly and LOS-based vaccines

The inner core structures of the lipooligosaccharides (LOS) of Neisseria me ningitidis are potential vaccine candidates because both bactericidal and o psonic antibodies can be generated against these epitopes. In an effort to better understand LOS biosynthesis and the potential immunogenicity of the LOS inner core, we have determined the LOS structure from a meningococcal r faK mutant CMK1. The rfaK gene encodes the transferase that adds an alpha - N-acetylglucosaminosyl residue to O-2 of the inner core heptose (Hep) It of the LOS. The LOS oligosaccharide from this mutant was previously shown to contain only Hep, 3-deoxy-D-manno-2-octulosonic acid (Kdo), and multiple ph osphoethanolamine (PEA) substituents (Kahler et al., 1996a, J. Bacteriol., 178, 1265-1273). The complete structure of the oligosaccharide (OS) compone nt of the LOS from mutant CMK1 was determined using glycosyl composition an d linkage analyses, and H-1, C-13, and P-31 nuclear magnetic resonance spec troscopy. The CMK1 OS structure contains a PEA group at O-3 of Hep II in pl ace of the usual glucosyl residue found at this position in the completed L 2 LOS glycoform from the parent NMB strain. The PEA group at O-6 of Hep II, however, is present in both the CMK1 mutant LOS and parental NMB L2 LOS st ructures. The structure of the OS from CMK1 suggests that PEA substituents are transferred to both the O-3 and O-6 positions of Hep II prior to: (1) t he incorporation of the alpha -GlcNAc on Hep II; (2) the synthesis of the a -chain on Hep 1; and (3) the substitution of the glycosyl residue at the O- 3 Hep II, which distinguishes L2 and L3 immunotypes. The LOS structure of t he CMK1 mutant makes it a candidate immunogen that could generate broadly c ross-reactive inner-core LOS antibodies.