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J. Biol. Chem., Vol. 283, Issue 1, 17-28, January 4, 2008

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Enzyme-dependent Variations in the Polysialylation of the Neural Cell Adhesion Molecule (NCAM) in Vivo^*

Sebastian P. Galuska, Rudolf Geyer, Rita Gerardy-Schahn, Martina Mühlenhoff, and Hildegard Geyer¹

From the Institute of Biochemistry, Medical Faculty, University of Giessen, Friedrichstrasse 24, Giessen D-35392 and the Institute of Cellular Chemistry, Medical School Hannover, Hannover D-30625, Germany

Polysialic acid (polySia), an 2,8-linked polymer of N-acetylneuraminic acid, represents an essential regulator of neural cell adhesion molecule (NCAM) functions. Two polysialyltransferases, ST8SiaII and ST8SiaIV, account for polySia synthesis, but their individual roles in vivo are still not fully understood. Previous in vitro studies defined differences between the two enzymes in their usage of the two NCAM N-glycosylation sites affected and suggested a synergistic effect. Using mutant mice, lacking either enzyme, we now assessed in vivo the contribution of ST8SiaII and ST8SiaIV to polysialylation of NCAM. PolySia-NCAM was isolated from mouse brains and trypsinized, and polysialylated glycopeptides as well as glycans were analyzed in detail. Our results revealed an identical glycosylation and almost complete polysialylation of N-glycosylation sites 5 and 6 in polySia-NCAM irrespective of the enzyme present. The same sets of glycans were substituted by identical numbers of polySia chains in vivo, the length distribution of which, however, differed with the enzyme setting. Expression of ST8SiaIV alone led to higher amounts of short polySia chains and gradual decrease with length, whereas exclusive action of ST8SiaII evoked a slight reduction in long polySia chains only. These variations were most pronounced at N-glycosylation site 5, whereas the polysialylation pattern at N-glycosylation site 6 did not differ between NCAM from wild-type and ST8SiaII- or ST8SiaIV-deficient mice. Thus, our fine structure analyses suggest a comparable quality of polysialylation by ST8SiaII and ST8SiaIV and a distinct synergistic action of the two enzymes in the synthesis of long polySia chains at N-glycosylation site 5 in vivo.

Received for publication, August 22, 2007 , and in revised form, October 30, 2007.

^* This work was supported in part by the Deutsche Forschungsgemeinschaft (Grants Ge 527/3 and SFB 535, Project Z1) and the European Community (6th framework program PROMEMORIA, to R. G.-S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Table S1.

¹ To whom correspondence should be addressed. Tel.: 49-641-994-7412; Fax: 49-641-994-7409; E-mail: hildegard.geyer{at}biochemie.med.uni-giessen.de.

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