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). 



Furukawa, A., K. Nakada-Tsukui, and T. Nozaki. (2012). Novel transmembrane receptor involved in phagosome transport of lysozymes and β-hexosaminidase in the enteric protozoan Entamoeba histolytica. PLoS Pathog 8: e1002539.


TC#NameOrganismal TypeExample

The cysteine protease binding protein-8 (CPBP8) with 904 aas and 2 TMSs, N- and C-terminal.


CPBP8 of Entamoeba histolyticus (C4M342)


Uncharacterized protein of 1462 aas and 2 TMSs, N- and C-terminal

UP of Fragilariopsis cylindrus


Uncharacterized T9SS C-terminal target domain-containing protein of 873 aas and 1 N-terminal TMS.

UP of Aequorivita viscosa


Uncharacterized protein of 1360 aas and 1 TMS.

UP of Thalassiosira pseudonana (Marine diatom) (Cyclotella nana)