Two novel calcium-binding proteins from cytoplasmic granules of the protozoan parasite Entamoeba histolytica

We report on the molecular characterisation of two novel granule proteins o f the protozoon and human pathogen Entamoeba histolytica. The proteins, whi ch were named grainin 1 and 2, show a considerable structural similarity to calcium-binding proteins, particularly within EF-hand motifs. Each grainin possesses three of these putative calcium-binding sites. Based on careful inspection of known structures of protein families containing EF-hands, a d omain of grainin 1 covering two EF-band motifs was modeled by homology. Cal cium-binding activity of grainins was demonstrated by two independent metho ds. These granule proteins may be implicated in functions vital for the pri mitive phagocyte and destructive parasite such as control of endocytotic pa thways and granule discharge. (C) 2000 Federation of European Biochemical S ocieties. Published by Elsevier Science B.V. All rights reserved.