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J. Biol. Chem., Vol. 282, Issue 9, 5984-5990, March 2, 2007

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XT-II, the Second Isoform of Human Peptide-O-xylosyltransferase, Displays Enzymatic Activity^*

Josef Voglmeir¹, Regina Voglauer, and Iain B. H. Wilson²

From the Department für Chemie and Institut für Angewandte Mikrobiologie, Universität für Bodenkultur, A-1190 Wien, Austria

Peptide O-xylosyltransferase (EC 2.4.2.26 [EC] ) is the first enzyme required for the generation of chondroitin and heparan sulfate glycosaminoglycan chains of proteoglycans. Cloning of cDNAs has previously shown that, whereas invertebrates generally have a single xylosyltransferase gene, vertebrate genomes encode two similar proteins, xylosyltransferase I and II (XT-I and XT-II). To date, enzymatic activity has only been demonstrated for the human XT-I, Caenorhabditis SQV-6, and Drosophila OXT isoforms. In the present study, we demonstrate that a soluble form of human XT-II expressed in the xylosyltransferase-deficient pgsA-745 (S745) Chinese hamster ovary cell line is indeed capable of catalyzing the transfer of xylose to a variety of peptide substrates; its enzyme activity was also proven using a Pichia-expressed form of XT-II. Its pH, temperature, and cation dependences are similar to those of XT-I expressed in either mammalian cells or yeast. Our data suggest that XT-I and XT-II are, at least in vitro, functionally identical.

Received for publication, August 23, 2006 , and in revised form, November 21, 2006.

Note Added in Proof—Two papers independently confirm the activity of mammalian XT-II and also show that the corresponding gene in the pgsA-745 cell line has a premature stop codon, while wild-type Chinese hamster ovary cells express only extremely low levels of the XT-I transcript (41, 42).

^* This work was supported by grants from the Hochschuljubliaümsstiftung der Stadt Wien (Grant H-1114) and the Fonds zur Förderung der wissenschaftlichen Forschung (Grant P18447 [GenBank] ) (to I. B. H. W.). 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 Present address: Manchester Interdisciplinary Biocentre, University of Manchester, Manchester M1 7ND, UK.

² To whom correspondence should be addressed. Tel.: 43-1-36006-6541; Fax: 43-1-36006-6076; E-mail: iain.wilson{at}boku.ac.at.

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