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J. Biol. Chem., Vol. 280, Issue 7, 5423-5429, February 18, 2005

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Multiple Signals Are Required for 2,6-Sialyltransferase (ST6Gal I) Oligomerization and Golgi Localization^*

Fiona H. Fenteany and Karen J. Colley

From the Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, College of Medicine, Chicago, Illinois 60607

A single amino acid difference in the catalytic domain of two isoforms of the 2,6-sialyltransferase (ST6Gal I) leads to differences in their trafficking, processing, and oligomerization. The STtyr isoform is transiently localized in the Golgi and is ultimately cleaved and secreted, whereas the STcys isoform is stably localized in the Golgi and is not cleaved and secreted. The stable localization of STcys is correlated with its enhanced ability to oligomerize. To test the hypothesis that multiple signals can mediate Golgi localization and further evaluate the role of oligomerization in the localization process, we evaluated the effects of individually and simultaneously altering the cytosolic tail and transmembrane region of the STcys isoform. We found that the localization, processing, and oligomerization of STcys were not substantially changed when either the core amino acids of the cytosolic tail were deleted or the sequence and length of the transmembrane region were altered. In contrast, when these changes were made simultaneously, the STcys isoform was converted into a form that was processed, secreted, and weakly oligomerized like STtyr. We propose that STcys oligomerization is a secondary event resulting from its concentration in the Golgi via mechanisms independently mediated by its cytosolic tail and transmembrane region.

Received for publication, November 2, 2004 , and in revised form, December 6, 2004.

^* This work was supported by the National Institutes of Health Research Grant RO1-GM48134 (to K. J. C.). 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.

To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Genetics, University of Illinois at Chicago, College of Medicine, 900 S. Ashland Ave., M/C 669, Chicago, IL 60607. Tel.: 312-996-7756; Fax: 312-413-0353; E-mail: karenc{at}uic.edu.

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