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Glycobiology Advance Access originally published online on March 23, 2007
Glycobiology 2007 17(7):735-743; doi:10.1093/glycob/cwm032
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Published by Oxford University Press 2007

Successive glycosyltransfer of sialic acid by Escherichia coli K92 polysialyltransferase in elongation of oligosialic acceptors

Justine Vionnet and Willie F Vann1

Laboratory of Bacterial Polysaccharides, Center for Biologics Evaluation and Research, FDA, Bethesda, MD 20892

1 To whom correspondence should be addressed; Tel: +301 496 2008; Fax: +301 402 2776; E-mail: wvann{at}helix.nih.gov

Received on November 10, 2006; revised on February 19, 2007; accepted on March 12, 2007

Escherichia coli K92 produces a capsular polysialic acid with alternating {alpha}2,8 {alpha}2,9 NeuNAc linkages. This polysaccharide is cross-reactive with the neuroinvasive pathogen Neisseria meningitidis Group C. The K92 polysialyltransferase (PST) catalyzes the synthesis of the polysialic acid with alternating linkages by the transfer of NeuNAc from CMP-NeuNAc to the nonreducing end of the growing polymer. We used a fluorescent-based high-performance liquid chromatography assay to characterize the process of chain extension. The PST elongates the acceptor GT3-FCHASE in a biphasic fashion. The initial phase polymers are characterized by accumulation of product containing 1–8 additional sialic acid residues. This phase is followed by a very rapid formation of high-molecular weight (MW) polymer as the accumulated oligosaccharides containing 8–10 sialic acids are consumed. The high-MW polymer contains 90–100 sialic acids and is sensitive to degradation by periodate and K1–5 endoneuraminidase, suggesting that the polymer contains the alternating structure. The polymerization reaction does not appear to be strictly processive, since oligosaccharides of each intermediate size were detected before accumulation of high-molecular weight polymer. Synthesis can be blocked by CMP-9-azido-NeuNAc. These results suggest that the K92 PST forms both {alpha}2,8 and {alpha}2,9 linkages in a successive and nonprocessive fashion.

Key words: capsular polysaccharide / chain extension / polysialyltransferase / processivity / sialic acid


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