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J. Biol. Chem., Vol. 282, Issue 38, 27825-27840, September 21, 2007

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Biosynthesis of Truncated N-Linked Oligosaccharides Results from Non-orthologous Hexosaminidase-mediated Mechanisms in Nematodes, Plants, and Insects^*

Martin Gutternigg, Dorothea Kretschmer-Lubich, Katharina Paschinger, Dubravko Rendi, Josef Hader, Petra Geier, Ramona Ranftl, Verena Jantsch, Günter Lochnit^¶, and Iain B. H. Wilson¹

From the Department für Chemie, Universität für Bodenkultur, Muthgasse 18, Wien A-1190, Austria, the Abteilung für Chromosomenbiologie, Vienna Biocenter II, Wien A-1030, Austria, and the ^¶Institut für Biochemie, Justus-Liebig-Universität, Giessen D-35292, Germany

In many invertebrates and plants, the N-glycosylation profile is dominated by truncated paucimannosidic N-glycans, i.e. glycans consisting of a simple trimannosylchitobiosyl core often modified by core fucose residues. Even though they lack antennal N-acetylglucosamine residues, the biosynthesis of these glycans requires the sequential action of GlcNAc transferase I, Golgi mannosidase II, and, finally, -N-acetylglucosaminidases. In Drosophila, the recently characterized enzyme encoded by the fused lobes (fdl) gene specifically removes the non-reducing N-acetylglucosamine residue from the 1,3-antenna of N-glycans. In the present study, we examined the products of five -N-acetylhexosaminidase genes from Caenorhabditis elegans (hex-1 to hex-5, corresponding to reading frames T14F9.3, C14C11.3, Y39A1C.4, Y51F10.5, and Y70D2A.2) in addition to three from Arabidopsis thaliana (AtHEX1, AtHEX2, and AtHEX3, corresponding to reading frames At1g65590, At3g55260, and At1g05590). Based on homology, the Caenorhabditis HEX-1 and all three Arabidopsis enzymes are members of the same sub-family as the aforementioned Drosophila fused lobes enzyme but either act as chitotriosidases or non-specifically remove N-acetylglucosamine from both N-glycan antennae. The other four Caenorhabditis enzymes are members of a distinct sub-family; nevertheless, two of these enzymes displayed the same 1,3-antennal specificity as the fused lobes enzyme. Furthermore, a deletion of part of the Caenorhabditis hex-2 gene drastically reduces the native N-glycan-specific hexosaminidase activity in mutant worm extracts and results in a shift in the N-glycan profile, which is a demonstration of its in vivo enzymatic relevance. Based on these data, it is hypothesized that the genetic origin of paucimannosidic glycans in nematodes, plants, and insects involves highly divergent members of the same hexosaminidase gene family.

Received for publication, May 23, 2007 , and in revised form, July 18, 2007.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank^TM/EBI Data Bank with accession number(s) AM748820, AM748821, AM748822, AM748823, and AM748824.

^* This work was supported by Grants P15475 [GenBank] and P18447 [GenBank] (to I. B. H. W.) from the Austrian Fonds zur Förderung der wissenschaftlichen Forschung. 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 Figs. S1 and S2.

¹ 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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