Recent and Future Advances in the Chemoenzymatic Synthesis of Homogeneous Glycans for Bacterial Glycoconjugate Vaccine Development

Vaccines are important in preventing disease outbreaks and controlling the spread of disease in a population. A variety of vaccines exist, including subunit, recombinant, and conjugate vaccines. Glycoconjugate vaccines have been an important tool to fight against diseases caused by a number of bacteria. Glycoconjugate vaccines are often heterogeneous. Vaccines of the future are becoming more rationally designed to have a defined oligosaccharide chain length and position of conjugation. Homogenous vaccines could play an important role in assessing the relationship between vaccine structure and immune response. This review focuses on recent advances in the chemoenzymatic production of defined bacterial oligosaccharides for vaccine development with a focus on Neisseria meningitidis and selected WHO-prioritized antibacterial resistant-pathogens. We also provide some perspective on future advances in the chemoenzymatic synthesis of well-defined oligosaccharides

Meningococcal Vaccines: Current Status and Emerging Strategies

Neisseria meningitidis causes most cases of bacterial meningitis. Meningococcal meningitis is a public health burden to both developed and developing countries throughout the world. There are a number of vaccines (polysaccharide-based, glycoconjugate, protein-based and combined conjugate vaccines) that are approved to target five of the six disease-causing serogroups of the pathogen. Immunization strategies have been effective at helping to decrease the global incidence of meningococcal meningitis. Researchers continue to enhance these efforts through discovery of new antigen targets that may lead to a broadly protective vaccine and development of new methods of homogenous vaccine production. This review describes current meningococcal vaccines and discusses some recent research discoveries that may transform vaccine development against N. meningitidis in the future

Determination of the binding affinities of Neisseria meningitidis serogroup W capsule polymerase with two nucleotide sugar substrates

Abstract Objective Meningococcal meningitis is a public health burden. Immunization strategies have reduced global incidence of the disease. Glycoconjugate vaccines are the most effective type of vaccine to combat most causes of meningococcal meningitis. These vaccines contain capsular polysaccharide fragments from disease-causing serogroups of Neisseria meningitidis that are chemically attached to a carrier protein. The enzymes responsible for capsular polysaccharide synthesis can serve as tools to make these critical vaccine components. One such enzyme is the N. meningitidis serogroup W capsule polymerase. This enzyme is responsible for creating the galactose-sialic acid containing capsular polysaccharide of this serogroup. Our aim in this study was to determine the binding affinities of nucleotide sugar donors CMP-sialic acid and UDP-galactose using a coupled transferase assay to inform future work to modulate polysaccharide synthesis by this enzyme. Results We determined a Km of 66.8 µM for CMP-sialic acid and a Km for UDP-galactose of 3.9 µM. These values are lower than reported values for other retaining galactosyltransferases and inverting sialyltransferases respectively. There were difficulties obtaining reliable data for galactosyltransferase activity. An alternate strategy is needed to assess kinetic parameters of the separate transferase activities for this enzyme

Characterization and Acceptor Preference of a Soluble Meningococcal Group C Polysialyltransferase▿ †

Vaccines against Neisseria meningitidis group C are based on its α-2,9-linked polysialic acid capsular polysaccharide. This polysialic acid expressed on the surface of N. meningitidis and in the absence of specific antibody serves to evade host defense mechanisms. The polysialyltransferase (PST) that forms the group C polysialic acid (NmC PST) is located in the cytoplasmic membrane. Until recently, detailed characterization of bacterial polysialyltransferases has been hampered by a lack of availability of soluble enzyme preparations. We have constructed chimeras of the group C polysialyltransferase that catalyzes the formation α-2,9-polysialic acid as a soluble enzyme. We used site-directed mutagenesis to determine the region of the enzyme necessary for synthesis of the α-2,9 linkage. A chimera of NmB and NmC PSTs containing only amino acids 1 to 107 of the NmB polysialyltransferase catalyzed the synthesis of α-2,8-polysialic acid. The NmC polysialyltransferase requires an exogenous acceptor for catalytic activity. While it requires a minimum of a disialylated oligosaccharide to catalyze transfer, it can form high-molecular-weight α-2,9-polysialic acid in a nonprocessive fashion when initiated with an α-2,8-polysialic acid acceptor. De novo synthesis in vivo requires an endogenous acceptor. We attempted to reconstitute de novo activity of the soluble group C polysialyltransferase with membrane components. We found that an acapsular mutant with a defect in the polysialyltransferase produces outer membrane vesicles containing an acceptor for the α-2,9-polysialyltransferase. This acceptor is an amphipathic molecule and can be elongated to produce polysialic acid that is reactive with group C-specific antibody