Abstract
Intestinal amoebiasis is caused by Entamoeba histolytica, one of the deadliest human-infective parasites. Central to its pathogenicity is its binding to mucosal carbohydrates, which precedes tissue damage by trogocytosis. Carbohydrate binding is mediated by a single adhesin, the galactose/N-acetylgalactosamine (Gal/GalNAc) lectin, which is the leading vaccine candidate for amoebiasis. We present the structure of the native heterodimeric lectin, revealing an ordered core containing the light chain and the N-terminal region of the heavy chain. Structures obtained in the presence of ligand show that the Gal/GalNAc binding site is in the light chain, which adopts a β-trefoil fold found in other lectins. An elongated arm emerges from the heavy chain, which adopts multiple positions and may be modulated by sugar binding. This study reveals the molecular basis for sugar binding by the Entamoeba histolytica Gal/GalNAc lectin, a prerequisite for parasite invasion and development of intestinal disease.