A lysosomal hydrolase receptor, CPBF2, is associated with motility and invasion of the enteric protozoan parasite Entamoeba histolytica.

Proper targeting and secretion of lysosomal hydrolases are regulated by transporting receptors. Entamoeba histolytica, the enteric protozoan parasite responsible for human amebiasis, has a unique family of lysosomal hydrolase receptors, cysteine protease binding protein family, CPBF. CPBFs, consisting of 11 members with conserved domain organization, bind to a wide range of cargos including cysteine proteases and glycosidases, which are also known to be involved in pathogenesis of this parasite. In this study, we characterized one of CPBFs, CPBF2, which is involved in cell motility and extracellular matrix invasion. Unexpectedly, these roles of CPBF were not related to its cargo, α-amylase. This is the first demonstration that a putative hydrolase receptor is involved in cell motility and invasion in parasitic protozoa.

Ligand heterogeneity of the cysteine protease binding protein family in the parasitic protist Entamoeba histolytica.

Lysosomal soluble proteins are targeted to endosomes and lysosomes by specific receptors resident in the endoplasmic reticulum and/or the Golgi apparatus. The enteric protozoan parasite Entamoeba histolytica has a novel class of lysosomal targeting receptors, named the cysteine protease binding protein family (CPBF). Among 11 CPBFs (CPBF1-11), ligands for three members, CPBF1, CPBF6 and CPBF8, were previously shown to be cysteine proteases, α- and γ- amylases, and ß-hexosaminidase and lysozymes, respectively. To further understand the heterogeneity of the ligands of CPBFs, we attempted to isolate and identify the ligands for other members of CPBFs, namely CPBF2, 3, 4, 5, 7, 9, 10 and 11, by immunoprecipitation and mass spectrometric analysis. We found that CPBF2 and CPBF10 bound to α-amylases while CPBF7 bound to ß-hexosaminidases. It is intriguing that cysteine protease are exclusively recognised by CPBF1, whereas three α-amylases and ß-hexosaminidases are redundantly recognised by three and two CPBFs, respectively. It was shown by bioinformatics analysis and phylogenetic reconstruction that each CPBF contains six prepeptidase carboxyl-terminal domains, and the domain configuration is evolutionarily conserved among CPBFs. Taken together, CPBFs with unique and conserved domain organisation have a remarkable ligand heterogeneity toward cysteine protease and carbohydrate degradation enzymes. Further structural studies are needed to elucidate the structural basis of the ligand specificity.