title: Food vacuole plasmepsins are processed at a conserved site by an acidic convertase activity in Plasmodium falciparum.
abstract: Intraerythrocytic Plasmodium falciparum digests vast amounts of hemoglobin within an acidic food vacuole (FV). Four homologous aspartic proteases participate in hemoglobin degradation within the FV. Plasmepsin (PM) I and II are thought to initiate degradation of the native hemoglobin molecule. PM IV and histo-aspartic protease (HAP) act on denatured globin further downstream in the pathway. PM I and II have been shown to be synthesized as zymogens and activated by proteolytic removal of a propiece. In this study, we have determined that the proteolytic processing of FV plasmepsins occurs immediately after a conserved Leu-Gly dipeptidyl motif with uniform kinetics and pH and inhibitor sensitivities. We have developed a cell-free in vitro processing assay that generates correctly processed plasmepsins. Our data suggest that proplasmepsin processing is not autocatalytic, but rather is mediated by a separate processing enzyme. This convertase requires acidic conditions and is blocked only by the calpain inhibitors, suggesting that it may be an atypical calpain-like protease.
authors.affiliation: Departments of Medicine and Molecular Microbiology, Howard Hughes Medical Institute, Washington University School of Medicine, Box 8230, 660 South Euclid Ave, St Louis, MO 63110, USA.
authors.forename: Ritu
authors.initials: R
authors.lastname: Banerjee
authors.forename: Susan E
authors.initials: SE
authors.lastname: Francis
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Goldberg
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry / Q000378:metabolism*; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D002474:Cell-Free System; D010450:Endopeptidases / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007976:Leupeptins / Q000494:pharmacology; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000254:growth & development; D011480:Protease Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D015800:Protozoan Proteins; D014617:Vacuoles / Q000201:enzymology*
chemical_list: D007976:Leupeptins; D011480:Protease Inhibitors; D015800:Protozoan Proteins; C063261:acetylleucyl-leucyl-norleucinal; D010450:Endopeptidases; D002154:Calpain; D016282:Aspartic Acid Endopeptidases; C089643:plasmepsin; C100637:plasmepsin II