Plasmepsin II (PMII) is a pepsin-family (peptidase A1) aspartic endopeptidase of the malaria parasite Plasmodium falciparum, one of four paralogous food-vacuole plasmepsins (PMI, PMII, PMIV, HAP) encoded in a tandem cluster on chromosome 14. It is synthesized during the asexual blood stage as a type II integral membrane proenzyme whose propeptide carries the transmembrane anchor; the zymogen traffics through the secretory pathway to cytostomal vacuoles and is carried with endocytosed host hemoglobin to the acidic food (digestive) vacuole, where it is cleaved, mainly by falcipains with autoprocessing as a backup, to release the soluble active enzyme. Together with PMI, PMII initiates hemoglobin degradation by cleaving native hemoglobin in the hinge region and acts synergistically with HAP, PMIV, falcipains and falcilysin to digest globin, supplying amino acids and liberating heme for hemozoin formation; it co-purifies with these enzymes and heme detoxification protein in a food-vacuole hemoglobinase complex. Gene disruption causes only a mild growth defect, reflecting extensive redundancy among the food-vacuole proteases. PMII is a well-studied antimalarial drug target with many inhibitor co-crystal structures.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004190 aspartic-type endopeptidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic inference of aspartic-type endopeptidase activity for PMII from the pepsin-family (A1) node; PMII itself is among the experimentally characterized descendants. Reason: PMII is a catalytically active pepsin-family aspartic protease with the canonical catalytic aspartates; its own experimental activity grounds this node, and the target appearing in WITH/FROM is expected. Core molecular function. Supporting Evidence: PMID:29943906 The direct indication of hemoglobin degradation by PMII confirms the activity of the mature enzyme. PMID:29943906 The mature PMII cleaves the fluorogenic substrate with the Km value of ~0.68 µM. |
| GO:0004190 aspartic-type endopeptidase activity | IDA PMID:29943906 Deciphering the mechanism of potent peptidomimetic inhibitor... | ACCEPT | Summary: Recombinant mature PMII degrades hemoglobin and cleaves an internally quenched peptide; inhibited by pepstatin A and KNI peptidomimetics (Mishra et al. 2018). Reason: Direct biochemical demonstration of aspartic endopeptidase activity of the mature enzyme. Core function. Supporting Evidence: PMID:29943906 The direct indication of hemoglobin degradation by PMII confirms the activity of the mature enzyme. PMID:29943906 The mature PMII cleaves the fluorogenic substrate with the Km value of ~0.68 µM. |
| GO:0004190 aspartic-type endopeptidase activity | IEA GO_REF:0000120 | ACCEPT | Summary: InterPro/ARBA-based assignment of aspartic-type endopeptidase activity (Peptidase A1 domain and aspartic protease active-site signatures). Reason: Consistent with the experimental data; PMII retains both catalytic aspartate motifs (PROSITE PS00141 x2) and is active. Supporting Evidence: PMID:29943906 The direct indication of hemoglobin degradation by PMII confirms the activity of the mature enzyme. |
| GO:0004190 aspartic-type endopeptidase activity | TAS PMID:9886289 Crystal structure of the novel aspartic proteinase zymogen p... | ACCEPT | Summary: Traceable author statement from the proplasmepsin II zymogen crystal structure paper describing PMII as a hemoglobin-digesting aspartic proteinase. Reason: Statement is consistent with direct biochemical evidence for PMII activity elsewhere; abstract-only cache but the statement is explicit. Supporting Evidence: PMID:9886289 an aspartic proteinase used by Plasmodiumfalciparum to digest hemoglobin during the blood stage of malaria. PMID:11782538 Two homologous aspartic proteases, called plasmepsins I and II (PM I and II) initiate the degradative process by cleaving the native hemoglobin molecule in a highly conserved hinge region ( 5 , 6 ). |
| GO:0005764 lysosome | IBA GO_REF:0000033 | MODIFY | Summary: IBA to lysosome from a plasmepsin-clade PANTHER node (PMI/PMII/PMIV). Reason: The parasite food (digestive) vacuole is a lysosome-like lytic organelle and in GO food vacuole is_a phagolysosome is_a lysosome, so the location is correct but general. Refine to food vacuole (GO:0020020), which PMII already carries by IDA. Not an animal-only mis-transfer: the PAINT node is the Plasmodium plasmepsin clade. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN008723823 SUPPORTS TRANSFER Plasmepsin-clade node whose descendants (PMI, PMII, PMIV) are food-vacuole residents; lysosome is the nearest generic term but the Plasmodium-specific food vacuole is the precise location. Proposed replacements: food vacuole Supporting Evidence: PMID:14709539 The food vacuole is a lysosome-like organelle unique to the genus Plasmodium. PMID:11782538 Immunoelectron microscopy confirmed that PM I, II, and IV and HAP are in the FV (Fig. 1 B ). |
| GO:0005774 vacuolar membrane | EXP PMID:14709539 Trafficking of plasmepsin II to the food vacuole of the mala... | KEEP AS NON CORE | Summary: The proenzyme (type II integral membrane protein) is found in cytostomal vacuole membranes and accumulates in the food vacuole membrane when maturation is blocked with ALLN (Klemba et al. 2004). Reason: Correct for the zymogen in transit, but the active enzyme is the soluble mature form released into the food vacuole lumen. No food-vacuole-membrane-specific GO term exists, so vacuolar membrane is as precise as available. Supporting Evidence: PMID:14709539 ALLN treatment results in accumulation of proPM II–GFP in the food vacuole membrane. PMID:14709539 PM I and II are synthesized as unglycosylated type II integral membrane proenzymes (Francis et al., 1997a), with the membrane-spanning domain in the proregion. |
| GO:0005774 vacuolar membrane | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt subcellular-location mapping (Vacuole membrane) to vacuolar membrane. Reason: Same claim as the EXP row; true of the membrane-anchored proenzyme, peripheral to where catalysis occurs. Supporting Evidence: PMID:14709539 ALLN treatment results in accumulation of proPM II–GFP in the food vacuole membrane. |
| GO:0005775 vacuolar lumen | EXP PMID:14709539 Trafficking of plasmepsin II to the food vacuole of the mala... | ACCEPT | Summary: Mature soluble PMII is released into the food vacuole lumen after cleavage of the membrane-anchored proregion (Klemba et al. 2004). Reason: The food vacuole lumen is the site of hemoglobin digestion and of active PMII. No food-vacuole-lumen GO term exists, so vacuolar lumen is appropriate. Supporting Evidence: PMID:14709539 In the acidic environment of the food vacuole, the proenzyme is cleaved and mature, active, soluble PM II is released. |
| GO:0005775 vacuolar lumen | EXP PMID:23471987 Protein complex directs hemoglobin-to-hemozoin formation in ... | ACCEPT | Summary: PMII co-purifies in a ~200 kDa hemoglobinase/hemozoin formation complex from food vacuole lysates (Chugh et al. 2013). Reason: Consistent with lumenal food vacuole localization of the mature enzyme. Supporting Evidence: PMID:23471987 We report the presence of a ∼200-kDa protein complex in the food vacuole that is required for Hb degradation and Hz formation. PMID:23471987 This complex contains several parasite proteins, including falcipain 2/2', plasmepsin II, plasmepsin IV, histo aspartic protease, and heme detoxification protein. |
| GO:0005775 vacuolar lumen | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular-location mapping (Vacuole lumen) to vacuolar lumen. Reason: Consistent with experimental data on the soluble mature enzyme in the food vacuole lumen. Supporting Evidence: PMID:14709539 In the acidic environment of the food vacuole, the proenzyme is cleaved and mature, active, soluble PM II is released. |
| GO:0006508 proteolysis | IBA GO_REF:0000033 | MODIFY | Summary: Phylogenetic inference of proteolysis from the A1 aspartic peptidase node. Reason: True but uninformative: the proteolysis PMII performs is the degradation of host hemoglobin in the food vacuole. Refine to hemoglobin catabolic process (GO:0042540), which the gene already carries; note that in GO this term sits under protein catabolic process rather than as an is_a child of proteolysis, so this is a refinement to the informative process rather than a strict descendant. Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN002492107 SUPPORTS TRANSFER Deep A1 aspartic peptidase node; proteolysis is inherited correctly, refinement to the hemoglobin catabolic process is specific to the plasmepsin food-vacuole clade. Proposed replacements: hemoglobin catabolic process Supporting Evidence: PMID:11782538 Two homologous aspartic proteases, called plasmepsins I and II (PM I and II) initiate the degradative process by cleaving the native hemoglobin molecule in a highly conserved hinge region ( 5 , 6 ). PMID:29943906 The direct indication of hemoglobin degradation by PMII confirms the activity of the mature enzyme. |
| GO:0006508 proteolysis | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO assignment of proteolysis from the Peptidase A1 domain. Reason: As for the IBA row: correct but general; the specific supported process is hemoglobin catabolic process. Proposed replacements: hemoglobin catabolic process Supporting Evidence: PMID:11782538 Two homologous aspartic proteases, called plasmepsins I and II (PM I and II) initiate the degradative process by cleaving the native hemoglobin molecule in a highly conserved hinge region ( 5 , 6 ). |
| GO:0016020 membrane | EXP PMID:14709539 Trafficking of plasmepsin II to the food vacuole of the mala... | MODIFY | Summary: proPMII-GFP behaves as an integral membrane protein and is seen in ER, cytostomal vacuole and food vacuole membranes (Klemba et al. 2004). Reason: Correct but general; the specific membrane compartment documented for the zymogen is the vacuolar (cytostomal and food vacuole) membrane, which the gene already carries. Proposed replacements: vacuolar membrane Supporting Evidence: PMID:14709539 PM I and II are synthesized as unglycosylated type II integral membrane proenzymes (Francis et al., 1997a), with the membrane-spanning domain in the proregion. PMID:14709539 ALLN treatment results in accumulation of proPM II–GFP in the food vacuole membrane. |
| GO:0016020 membrane | IEA GO_REF:0000044 | MODIFY | Summary: UniProt subcellular-location mapping (Membrane; single-pass type II) to membrane. Reason: Correct but general; refine to vacuolar membrane as for the EXP row. Proposed replacements: vacuolar membrane Supporting Evidence: PMID:14709539 PM I and II are synthesized as unglycosylated type II integral membrane proenzymes (Francis et al., 1997a), with the membrane-spanning domain in the proregion. |
| GO:0020020 food vacuole | IDA PMID:11782538 Four plasmepsins are active in the Plasmodium falciparum foo... | ACCEPT | Summary: Immunofluorescence and immunoEM place PMII in the food vacuole together with PMI, PMIV and HAP (Banerjee et al. 2002). Reason: Direct localization to the site of hemoglobin digestion. Core location. Supporting Evidence: PMID:11782538 Immunoelectron microscopy confirmed that PM I, II, and IV and HAP are in the FV (Fig. 1 B ). |
| GO:0020020 food vacuole | IDA PMID:14709539 Trafficking of plasmepsin II to the food vacuole of the mala... | ACCEPT | Summary: Chromosomally tagged proPMII-GFP is delivered to and matured in the food vacuole (Klemba et al. 2004). Reason: Direct live-cell and immunoEM localization. Core location. Supporting Evidence: PMID:14709539 proPM II is transported through the secretory system to cytostomal vacuoles and then is carried along with its substrate hemoglobin to the food vacuole where it is proteolytically processed to mature PM II. |
| GO:0020020 food vacuole | IDA PMID:23471987 Protein complex directs hemoglobin-to-hemozoin formation in ... | ACCEPT | Summary: PMII identified in a hemoglobinase/heme detoxification complex isolated from purified food vacuoles (Chugh et al. 2013). Reason: Consistent with food vacuole residence. Supporting Evidence: PMID:23471987 We report the presence of a ∼200-kDa protein complex in the food vacuole that is required for Hb degradation and Hz formation. |
| GO:0020020 food vacuole | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA machine-learning assignment of food vacuole. Reason: Correct; matches experimental localization. Supporting Evidence: PMID:11782538 Immunoelectron microscopy confirmed that PM I, II, and IV and HAP are in the FV (Fig. 1 B ). |
| GO:0031910 cytostome | IDA PMID:14709539 Trafficking of plasmepsin II to the food vacuole of the mala... | KEEP AS NON CORE | Summary: proPMII-GFP labels the membrane of cytostomal vacuoles during uptake of erythrocyte cytosol (Klemba et al. 2004). Reason: Genuine localization of the zymogen en route to the food vacuole (the cytostome is a real apicomplexan endocytic structure), but a trafficking intermediate rather than the site of activity. Supporting Evidence: PMID:14709539 Cross sections of cytostomal vacuoles formed during the uptake of erythrocyte cytosol showing labeling of the vacuole membrane. PMID:14709539 proPM II is transported through the secretory system to cytostomal vacuoles and then is carried along with its substrate hemoglobin to the food vacuole where it is proteolytically processed to mature PM II. |
| GO:0042540 hemoglobin catabolic process | TAS PMID:9886289 Crystal structure of the novel aspartic proteinase zymogen p... | ACCEPT | Summary: PMII digests host hemoglobin in the food vacuole during the blood stage. Reason: PMII directly catalyses hemoglobin cleavage steps (initial hinge-region cleavage with PMI, and synergistic globin degradation with HAP/PMIV), so it performs part of the process. Hemoglobin is endocytosed host protein but is catabolised inside the parasite food vacuole, so this standard catabolic term (not a host-interaction term) is appropriate. Redundancy with paralogs explains the mild knockout phenotype but does not argue against participation. Supporting Evidence: PMID:9886289 an aspartic proteinase used by Plasmodiumfalciparum to digest hemoglobin during the blood stage of malaria. PMID:11782538 Two homologous aspartic proteases, called plasmepsins I and II (PM I and II) initiate the degradative process by cleaving the native hemoglobin molecule in a highly conserved hinge region ( 5 , 6 ). PMID:11782538 A combination of HAP and PM II, or PM IV and PM II cleaved hemoglobin much faster than each enzyme alone. |
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Download this section (compressed HTML)Q: Which specific peptide bonds in native hemoglobin are cleaved by PMII in vivo, and how does its specificity differ from PMI, given their overlapping roles in initiating degradation?
Q: Is the reported association of PMII with the food-vacuole hemozoin formation complex a stable stoichiometric complex warranting a GO cellular component term, or a transient co-purification?
Q: Does PMII act on host erythrocyte proteins outside the food vacuole (e.g. membrane skeleton proteins), or is its activity confined to the food vacuole lumen in vivo?
Experiment: Use conditional (DiCre or knock-sideways) depletion of PMII in a PMI-null background and measure accumulation of undigested hemoglobin, hemozoin formation and peptidomic cleavage-site maps of food vacuole contents.
Hypothesis: PMII and PMI are jointly required to initiate native hemoglobin cleavage in vivo
Type: conditional knockdown with peptidomics
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