Food vacuole plasmepsins are processed at a conserved site by an acidic convertase activity in Plasmodium falciparum.
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.
Banerjee
Ritu
R
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.
Francis
Susan E
SE
Goldberg
Daniel E
DE
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*
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