Autocatalytic polysialylation of polysialyltransferase-1

Polysialic acid (PSA) is a specific and highly regulated post-translational modification of the neural cell adhesion molecule NCAM, Synthesis of PSA depends on the activity of a single enzyme, the polysialyltransferase-1 (PST-1), recently cloned from three mammalian species, The present study was carried out to investigate the catalytic mechanism of PST-1, Using a newly developed in vitro assay system, we demonstrate autopolysialylation for PST-1, The synthesis of PSA chains, which involved N-glycosylation sites, occurred immediately after contact with the activated sugar donor CMP-Neu5Ac, In contrast to the polysialylation 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. Nevertheless, the autocatalytic step is likely to be a prerequisite for enzymatic activity, since agalacto-PST-1 isolated from Lec8 cells was functionally inactive, Our data describe a novel route of autocatalytic maturation of a glycosyltransferase and thereby provide a new basis for studies aimed at elucidating and influencing the catalytic functions of PST-1.