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J. Biol. Chem., Vol. 280, Issue 49, 40417-40427, December 9, 2005

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Absence of Nucleoside Diphosphatase Activities in the Yeast Secretory Pathway Does Not Abolish Nucleotide Sugar-dependent Protein Glycosylation^*

From the Laboratory of Glycobiology, Fundación Instituto Leloir, Avda. Patricias Argentinas 435, Buenos Aires C1405BWE, Argentina

It is accepted that glycosyltransferase-generated nucleoside diphosphates are converted to monophosphates in the secretory pathway by nucleoside diphosphatases (NDPases) to provide substrates for antiport transport systems by which entrance of nucleotide sugars from the cytosol into the lumen is coupled to exit of nucleoside monophosphates. Working with Saccharomyces cerevisiae mutants affected in anterograde and/or retrograde endoplasmic reticulum (ER)-Golgi vesicular traffic and/or defective in one or both secretory pathway (Golgi) NDPases, we show that UDP-Glc: glycoprotein glucosyltransferase-mediated glucosylation is not dependent on the presence of NDPases or on ER-Golgi vesicular traffic and that GDP-Man-dependent N- and O-mannosylations are reduced but not abolished in the absence of NDPases in the secretory pathway. Further, the absence of the main Man-1-P transferase (a Golgi GMP-generating enzyme) does not modify the limited mannosylation observed in the absence of NDPases. Based on these results and on available additional information, we suggest that in the absence of NDPases, the already characterized nucleotide sugar transporters allow entrance of nucleotide sugars into the luminal compartments and that resulting nucleoside diphosphates exit to the cytosol by a still unknown mechanism. Further, an unexpected side result suggests that formation of Ser/Thr-Man₂ may occur in the ER and not exclusively in the Golgi.

Received for publication, March 22, 2005 , and in revised form, September 16, 2005.

^* This work was supported by National Institutes of Health Grant GM44500 and Howard Hughes Medical Institute Grant 55003687 and Agencia Nacional de Promoción Científica y Tecnológica (Argentina) Grants 01-11264 and 03-14288. 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.

¹ To whom correspondence should be addressed: Laboratory of Glycobiology, Fundación Instituto Leloir, Avda. Patricias Argentinas 435, C1405BWE Buenos Aires, Argentina. Tel.: 5411-52387500 (ext. 3302); Fax: 5411-52387501; E-mail: aparodi{at}leloir.org.ar.

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