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J. Biol. Chem., Vol. 283, Issue 26, 18355-18364, June 27, 2008

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Unique Asn-linked Oligosaccharides of the Human Pathogen Entamoeba histolytica^*

Paula Magnelli, John F. Cipollo, Daniel M. Ratner, Jike Cui, Daniel Kelleher^¶, Reid Gilmore^¶, Catherine E. Costello, Phillips W. Robbins, and John Samuelson¹

From the Department of Molecular and Cell Biology and the Mass Spectrometry Resource, Department of Biochemistry, Boston University Medical Center, Boston, Massachusetts 02118-2526 and the ^¶Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts 01605-2324

N-Glycans of Entamoeba histolytica, the protist that causes amebic dysentery and liver abscess, are of great interest for multiple reasons. E. histolytica makes an unusual truncated N-glycan precursor (Man₅GlcNAc₂), has few nucleotide sugar transporters, and has a surface that is capped by the lectin concanavalin A. Here, biochemical and mass spectrometric methods were used to examine N-glycan biosynthesis and the final N-glycans of E. histolytica with the following conclusions. Unprocessed Man₅GlcNAc₂, which is the most abundant E. histolytica N-glycan, is aggregated into caps on the surface of E. histolytica by the N-glycan-specific, anti-retroviral lectin cyanovirin-N. Glc₁Man₅GlcNAc₂, which is made by a UDP-Glc: glycoprotein glucosyltransferase that is part of a conserved N-glycan-dependent endoplasmic reticulum quality control system for protein folding, is also present in mature N-glycans. A swainsonine-sensitive -mannosidase trims some N-glycans to biantennary Man₃GlcNAc₂. Complex N-glycans of E. histolytica are made by the addition of 1,2-linked Gal to both arms of small oligomannose glycans, and Gal residues are capped by one or more Glc. In summary, E. histolytica N-glycans include unprocessed Man₅GlcNAc₂, which is a target for cyanovirin-N, as well as unique, complex N-glycans containing Gal and Glc.

Received for publication, January 28, 2008 , and in revised form, March 21, 2008.

^* This work was supported, in whole or in part, by National Institutes of Health Grants AI 44070 (to J. S.), GM 43768 (to R. G.), P41 RR10888 and S10 RR15942 (to C. E. C.), and GM 31318 (to P. W. R.). 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 Table 1, Figs. 1-5, and additional references.

¹ To whom correspondence should be addressed: Dept. of Molecular and Cell Biology, Boston University Goldman School of Dental Medicine, 715 Albany St., Evans 426, Boston, MA 02118. Tel.: 617-414-1054; Fax: 617-414-1041; E-mail: jsamuels{at}bu.edu.

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