Scientific Publications by FDA Staff

J Bacteriol 2006 Sep;188(17):6195-206

Separate pathways for O acetylation of polymeric and monomeric sialic acids and identification of sialyl O-acetyl esterase in Escherichia coli K1.

Steenbergen SM, Lee YC, Vann WF, Vionnet J, Wright LF, Vimr ER

Vimr ER, Univ Illinois, Dept Pathobiol, Lab Sialobiol, 2522 VMBSB,2001 S Lincoln Ave, Urbana, IL 61802 USA Univ Illinois, Dept Pathobiol, Lab Sialobiol, Urbana, IL 61802 USA Univ Illinois, Dept Pathobiol, Lab Sialobiol & Comparat Metabolom, Urbana, IL 61802 USA Dong A Univ, Dept Biotechnol, Pusan, South Korea US FDA, Ctr Biol Evaluat & Res, Bethesda, MD 20014 USA Univ Rochester, Dept Microbiol & Immunol, Rochester, NY 14627 USA

O acetylation at carbon positions 7 or 9 of the sialic acid residues in the polysialic acid capsule of Escherichia coli K1 is catalyzed by a phase-variable contingency locus, neuO, carried by the K1-specific prophage, CUS-3. Here we describe a novel method for analyzing polymeric sialic acid O acetylation that involves the release of surface sialic acids by endo-N-acetylneuraminidase digestion, followed by fluorescent labeling and detection of quinoxalinone derivatives by chromatography. The results indicated that NeuO is responsible for the majority of capsule modification that takes place in vivo. However, a minor neuO-independent O acetylation pathway was detected that is dependent on the bifunctional polypeptide encoded by neuD. This pathway involves O acetylation of monomeric sialic acid and is regulated by another bifunctional enzyme, NeuA, which includes N-terminal synthetase and C-terminal sialyl O-esterase domains. A homologue of the NeuA C-terminal domain (Pm1710) in Pasteurella multocida was also shown to be an esterase, suggesting that it functions in the catabolism of acetylated environmental sialic acids. Our combined results indicate a previously unexpected complexity in the synthesis and catabolism of microbial sialic and polysialic acids. These findings are key to understanding the biological functions of modified sialic acids in E. coli K1 and other species and may provide new targets for drug or vaccine development.