9.B.3 The Cysteine Protease Binding Protein-8 (CPB8) Family

Phagocytes in eukaryotes are involved in the degradation of ingested bacteria in phagosomes. In Entamoeba histolytica, the intestinal protozoan parasite that causes amoebiasis, phagocytosis plays a role in nutrient acquisition and evasion from the host defense systems. Furukawa et al. (2012) identified and characterized a putative receptor/carrier for the transport of hydrolases to phagosomes. The receptor, in the cysteine protease binding protein family 8 (CPBP8), is localized to lysosomes and mediates transport of lysozymes and β-hexosaminidase α-subunits to phagosomes when the amoeba ingest mammalian cells or the Gram-positive bacillus, Clostridium perfringens. The binding of CPBP8 to the cargos is mediated by the serine-rich domain, including three serine residues. Loss of CPBP8 by gene silencing reduced the lysozyme and β-hexosaminidase activity in phagosomes and delayed the degradation of C. perfringens. Repression also resulted in a decrease in the cytopathy against mammalian cells, suggesting that CPBP8 may also be involved in pathogenesis against the mammalian hosts (Furukawa et al., 2012).