AUTOCATALYTIC POLYSIALYLATION OF POLYSIALYLTRANSFERASE-1

Polysialic acid (PSA) is a specific and highly regulated post-translat ional modification of the neural cell adhesion molecule NCAM, Synthesi s of PSA depends on the activity of a single enzyme, the polysialyltra nsferase-1 (PST-1), recently cloned from three mammalian species, The present study was carried out to investigate the catalytic mechanism o f PST-1, Using a newly developed in vitro assay system, we demonstrate autopolysialylation for PST-1, The synthesis of PSA chains, which inv olved N-glycosylation sites, occurred immediately after contact with t he activated sugar donor CMP-Neu5Ac, In contrast to the polysialylatio n of NCAM, where terminal sialylation in either the alpha 2,3 or alpha 2,6 position is required, the autopolysialylation could be started in the asialo-PST-1 isolated from CHO cells of the Lec2 complementation group. Pre-formed PSA chains were not transferred to NCAM. Nevertheles s, the autocatalytic step is likely to be a prerequisite for enzymatic activity, since agalacto-PST-1 isolated from Lec8 cells was functiona lly inactive, Our data describe a novel route of autocatalytic maturat ion of a glycosyltransferase and thereby provide a new basis for studi es aimed at elucidating and influencing the catalytic functions of PST -1.