Identification of a lipopolysaccharide alpha-2,3-sialyltransferase from Haemophilus influenzae.

Journal article

We have identified a gene for the addition of N-acetylneuraminic acid (Neu5Ac) in an alpha-2,3-linkage to a lactosyl acceptor moiety of the lipopolysaccharide (LPS) of the human pathogen Haemophilus influenzae. The gene is one that was identified previously as a phase-variable gene known as lic3A. Extracts of H. influenzae, as well as recombinant Escherichia coli strains producing Lic3A, demonstrate sialyltransferase activity in assays using synthetic fluorescent acceptors with a terminal galactosyl, lactosyl or N-acetyl-lactosaminyl moiety. In the RM118 strain of H. influenzae, Lic3A activity is modulated by the action of another phase-variable glycosyltransferase, LgtC, which competes for the same lactosyl acceptor moiety. Structural analysis of LPS from a RM118:lgtC mutant and the non-typeable strain 486 using mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy confirmed that the major sialylated species has a sialyl-alpha-(2-3)-lactosyl extension off the distal heptose. This sialylated glycoform was absent in strains containing a lic3A gene disruption. Low amounts of sialylated higher molecular mass glycoforms were present in RM118:lgtC lic3A, indicating the presence of a second sialyltransferase. Lic3A mutants of H. influenzae strains show reduced resistance to the killing effects of normal human serum. Lic3A, encoding an alpha-2,3-sialyltransferase activity, is the first reported phase-variable sialyltransferase gene.

Authors: Hood, D; Cox, A; Gilbert, M; Makepeace, K; Walsh, S

• Publication status: Published
• Journal: Molecular microbiology
• Volume: 39
• Issue: 2
• Pages: 341-350
• Publication date: 2001-01-01
• DOI: 10.1046/j.1365-2958.2001.02204.x
• EISSN: 1365-2958
• ISSN: 0950-382X
• Language: English
• Keywords: Carbohydrate Sequence; Electrophoresis, Capillary; Mass Spectrometry; Mutation; Haemophilus influenzae; Humans; Blood Bactericidal Activity; Molecular Sequence Data; Lipopolysaccharides; Sialyltransferases