Unique Asn-linked Oligosaccharides of the Human Pathogen Entamoeba histolytica

摘要

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 α-mannosidase trims some N-glycans to biantennary Man3GlcNAc2. Complex N-glycans of E. histolytica are made by the addition of α1,2-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.