title: Cysteine proteinases from distinct cellular compartments are recruited to phagocytic vesicles by Entamoeba histolytica.
abstract: Cysteine proteinases, which are encoded by at least seven genes, play a critical role in the pathogenesis of invasive amebiasis caused by Entamoeba histolytica. The study of these enzymes has been hampered by the inability to obtain significant quantities of the individual native proteinases. We have now expressed functionally active recombinant ACP1 (EhCP3) and ACP2 (EhCP2) proteinases in baculoviral expression vectors. The purified recombinant ACP1 and ACP2 proteinases exhibited similar activities for fluorogenic peptide substrates, especially in their preference for an arginine residue at the P2 position. Although ACP1 and ACP2 are structurally cathepsin L, homology modeling revealed that the aspartic acid in the S2 pocket would result in a substrate specificity for positively charged amino acids, like cathepsin B. The hydrolysis of peptide substrates was strongly inhibited by small peptidyl inhibitors specifically designed for parasitic cysteine proteinases. Confocal and immunoelectron microscopy localization of the proteinases with monoclonal and monospecific antibodies raised to the recombinant enzymes and peptides demonstrated that ACP2 was membrane-associated while ACP1 was cytoplasmic. Following phagocytosis of erythrocytes, ACP1, as well as the membrane-associated cysteine proteinase, ACP2, were incorporated into phagocytic vesicles. These studies suggest that E. histolytica has a redundancy of cysteine proteinases for intracellular digestion and that they may be recruited from different cellular compartments to the site of digestion of phagocytosed cells. The production of active proteinases in baculovirus and large scale recombinant enzymes in bacteria should further our understanding of the role of different cysteine proteinase gene products in virulence.
authors.affiliation: Department of Pathology, University of California, San Diego, UCSD Medical Center, 200 West Arbor Drive, San Diego, CA 92103-8416, USA.
authors.forename: Xuchu
authors.initials: X
authors.lastname: Que
authors.forename: Linda S
authors.initials: LS
authors.lastname: Brinen
authors.forename: Penny
authors.initials: P
authors.lastname: Perkins
authors.forename: Scott
authors.initials: S
authors.lastname: Herdman
authors.forename: Ken
authors.initials: K
authors.lastname: Hirata
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Torian
authors.forename: Harvey
authors.initials: H
authors.lastname: Rubin
authors.forename: James H
authors.initials: JH
authors.lastname: McKerrow
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Reed
mesh_terms: D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism / Q000648:ultrastructure; D004748:Entamoeba histolytica / Q000166:cytology* / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D018613:Microscopy, Confocal; D008958:Models, Molecular; D010587:Phagocytosis; D010588:Phagosomes / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D011487:Protein Conformation; D021381:Protein Transport; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D015853:Cysteine Proteinase Inhibitors; D008565:Membrane Proteins; D011994:Recombinant Proteins; D003546:Cysteine Endopeptidases