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J. Biol. Chem., Vol. 280, Issue 13, 12201-12211, April 1, 2005

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Structural Characterization of NETNES, a Novel Glycoconjugate in Trypanosoma cruzi Epimastigotes^*

James I. MacRae, Alvaro Acosta-Serrano¶, Nicholas A. Morrice||, Angela Mehlert, and Michael A. J. Ferguson**

From the Division of Biological Chemistry and Molecular Microbiology and the ^||Medical Research Council Protein Phosphorylation Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland, United Kingdom

The unicellular stercorarian protozoan parasite Trypanosoma cruzi is the etiological agent of Chagas' disease. The epimastigote form of the parasite is covered in a dense coat of glycoinositol phospholipids and short glycosylphosphatidylinositol (GPI)-anchored mucinlike molecules. Here, we describe the purification and structural characterization of NETNES, a relatively minor but unusually complex glycoprotein that coexists with these major surface components. The mature glycoprotein is only 13 amino acids in length, with the sequence AQENETNESGSID, and exists in two forms with either four or five post-translational modifications. These are either one or two asparagine-linked oligomannose glycans, two linear -mannose glycans linked to serine residues via phosphodiester linkages, and a GPI membrane anchor attached to the C-terminal aspartic acid residue. The variety and density of post-translational modifications on an unusually small peptide core make NETNES a unique type of glycoprotein. The N-glycans are predominantly Man1–6(Man1–3) Man1–6(Man1–3)Man1–4GlcNAc1–4GlcNAc1-Asn; the phosphate-linked glycans are a mixture of (Man1–2)_0–3Man1-P-Ser; and the GPI anchor has the structure Man1–2(ethanolamine phosphate)Man1–2Man1–6Man1–4(2-aminoethylphosphonate-6)GlcN1–6-myo-inositol-1-P-3(sn-1-O-(C_16:0)alkyl-2-O-(C_16:0)acylglycerol). Four putative NETNES genes were found in the T. cruzi genome data base. These genes are predicted to encode 65-amino acid proteins with cleavable 26-amino acid N-terminal signal peptides and 26-amino acid C-terminal GPI addition signal peptides.

Received for publication, November 16, 2004 , and in revised form, January 12, 2005.

^* This work was supported in part by Wellcome Trust Program Grant 071463. Work performed in the Post-Genomics and Molecular Interactions Centre of the University of Dundee was supported by Wellcome Trust Grant 060269. 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.

Supported by a States of Guernsey Education Council Ph.D. studentship.

^¶ Wellcome Trust Career Development Fellow supported by a Wellcome Trust traveling research fellowship. Present address: Wellcome Centre for Molecular Parasitology, University of Glasgow, Glasgow G11 6NU, Scotland, UK.

^** To whom correspondence should be addressed: Division of Biological Chemistry and Molecular Microbiology, School of Life Sciences, University of Dundee, Dow St., Dundee DD1 5EH, Scotland, UK. Tel.: 44-1382-344-219; Fax: 44-1382-348-896; E-mail: m.a.j.ferguson{at}dundee.ac.uk.

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