Scientific Publications by FDA Staff

Glycobiology 2014 Feb;24(2):139-49

Characterization of the Meningococcal Serogroup X Capsule N-Acetylglucosamine-1-Phosphotransferase.

Muindi KM, McCarthy PC, Wang T, Vionnet J, Battistel M, Jankowska E, Vann WF

Neisseria meningitidis serogroups A, B, C, Y, W135 and X are responsible for most cases of meningococcal meningitis. N. meningitidis serogroup X has recently emerged as a contributor to outbreaks of disease in Africa, but there is currently no vaccine against serogroup X. Understanding of the biosynthesis of the serogroup X capsular polysaccharide would provide useful tools for vaccine production. The serogroup X polysaccharide is a homopolymer of (a1¿4)-linked N-acetyl-D-glucosamine (GlcNAc) -1-phosphate. It has been shown that the gene cluster xcbABC encodes synthesis of this polysaccharide. The xcbA gene product has significant homology with sacB which is responsible for synthesis of the Neisseria serogroup A capsular polysaccharide, an (a1¿6)-N-acetylmannosamine-1-phosphate homopolymer. The xcbA protein also shares homology with the catalytic domain of human N-acetylglucosamine-1-phosphoryltransferase, a key enzyme in the mannose-6-phosphate receptor pathway. In this study we show that xcbA in the appropriate background is sufficient for the synthesis of N. meningitidis serogroup X polysaccharide. We detected polysaccharide in fractions of E. coli expressing the xcbA gene by ELISA. We isolated polysaccharide from an E. coli strain expressing XcbA and demonstrated that this polysaccharide has a 13C-NMR spectrum identical to that of polysaccharide isolated from N. meningitidis Group X. We also demonstrate that the purified XcbA protein is an N-acetylglucosamine-1-phosphotransferase that transfers N-acetylglucosamine-1-phosphate from UDP-GlcNAc to the 4-hydroxyl of an N-acetylglucosamine-1-phosphate oligosaccharide. Oligosaccharides fluorescently labeled at the aglycon are extended by XcbA only after the 4-phosphate occupying the non-reducing GlcNAc has been removed. The minimum size of fluorescent acceptors is a trisaccharide.