What Entamoeba and Giardia tell us about the diversity of Asn‐linked glycosylation.

Abstract

Entamoeba histolytica and Giardia lamblia are protists, which cause dysentery and diarrhea, respectively. While fungi, plants, and animals synthesize Asn-linked glycans (N-glycans) by means of a lipid-linked precursor with 14 sugars (GlcNAc2Man9Glc3), Entamoeba makes a precursor with 7 sugars (GlcNAc2Man5) and Giardia makes a precursor with just 1–2 sugars (GlcNAc1–2). The goal here was to determine how these truncated precursors affect the N-glycans of Entamoeba and Giardia, as well as N-glycan-associated quality control (QC) of protein folding and degradation. Entamoeba makes unique N-glycans, which include 1) unprocessed GlcNAc2Man5 that may be capped with the anti-retroviral agent cyanovirin and 2) complex glycans in which Gal and Glc are added to to bientenery GlcNAc2Man3. Entamoeba has N-glycan-associated QC of protein folding but not degradation. Giardia glycoproteins with N-glycans, which are composed of unprocessed GlcNAc and GlcNAc2, are efficiently captured with a wheat germ agglutinin affinity column. Giardia is missing N-glycan-associated QC of protein folding and degradation, although both Giardia and Entamoeba have N-glycan-independent QC proteins. We conclude that N-glycan precursor diversity of Entamoeba and Giardia has profound effects on their N-glycans and QC proteins.