{"gene":"PF3D7_0816300","run_date":"2026-09-08T16:26:55","timeline":{"discoveries":[{"year":2022,"finding":"HAP2P (PfHAP2p / PF3D7_0816300) is expressed in stage V gametocytes and localizes throughout the flagellum of male gametes in P. falciparum.","method":"Immunofluorescence / subcellular localization experiments in stage V gametocytes and male microgametes","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization experiment with functional context (flagellar localization tied to fusion role), single lab, two orthogonal methods (localization + gene deletion)","pmids":["36241929"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"Gene deletion of HAP2P (PF3D7_0816300) individually abolishes male fertility and prevents parasite transmission to the mosquito, establishing a non-redundant essential role distinct from the paralog PfHAP2.","method":"Gene deletion analysis and genetic crosses with mosquito transmission assays","journal":"Cellular and molecular life sciences : CMLS","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean knockout with defined phenotype (loss of male fertility and transmission), replicated across two independent gene deletions (HAP2P and HAP2) with genetic crosses confirming non-redundancy","pmids":["36241929"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"finding":"HAP2P (PF3D7_0816300) functions as an authentic plasma membrane fusogen: using a cell fusion assay, it was demonstrated that HAP2P (together with PfHAP2) is required on both fusing cells for successful fusion, resembling the bidirectional mechanism of C. elegans somatic fusogens.","method":"Mammalian cell fusion assay with expression of PfHAP2 and PfHAP2p on fusing cells","journal":"Cellular and molecular life sciences : CMLS","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct cell fusion assay establishing fusogen activity, single lab, single method (cell fusion assay)","pmids":["36241929"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2026,"finding":"The protein levels of HAP2P (PF3D7_0816300) are regulated downstream of PfDPL (a cryptochrome-like protein controlled by the PfGID E3 ubiquitin ligase complex): deletion of PfDPL causes a significant decrease in HAP2P protein levels at gametocyte days 6 and 12.","method":"Quantitative proteomics of ΔPfDPL gametocytes compared to parental controls at days 6 and 12","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — quantitative proteomics with genetic knockout establishing pathway placement of HAP2P downstream of PfDPL, single lab","pmids":["41986327"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2026,"finding":"The crystal structure of domain 3 of PfHAP2 (the cognate domain in the related PfHAP2 paralog, not PF3D7_0816300 itself) was determined in complex with a nanobody; nanobodies binding domain 3 of PfHAP2 with nanomolar affinity were identified, with some cross-species reactivity to other Plasmodium HAP2 proteins. NOTE: This structural result pertains to PfHAP2 (the paralog), not to HAP2P (PF3D7_0816300) directly.","method":"X-ray crystallography of nanobody–PfHAP2 domain 3 complex; affinity measurements","journal":"The Biochemical journal","confidence":"Low","confidence_rationale":"Tier 1 / Weak — crystal structure is high quality but concerns the PfHAP2 paralog's domain 3, not PF3D7_0816300; relevance to HAP2P is only indirect (same family); excluded from core model","pmids":["41498187"],"is_preprint":false,"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"current_model":"HAP2P (PF3D7_0816300) is an essential, non-redundant plasma membrane fusogen expressed in P. falciparum stage V gametocytes and localized throughout the flagellum of male microgametes; genetic deletion abolishes male fertility and mosquito transmission, and cell fusion assays demonstrate it acts as an authentic fusogen requiring expression on both fusing cells, while its protein levels are regulated upstream by the PfDPL–PfGID E3 ubiquitin ligase axis during gametocyte development."},"narrative":{"mechanistic_narrative":"HAP2P (PF3D7_0816300) is an essential, non-redundant plasma membrane fusogen that mediates male gamete fusion during the sexual stage of Plasmodium falciparum development [PMID:36241929]. It is expressed in stage V gametocytes and localizes throughout the flagellum of male microgametes [PMID:36241929]. Individual gene deletion of HAP2P abolishes male fertility and blocks parasite transmission to the mosquito, establishing a role that cannot be compensated by its paralog PfHAP2 [PMID:36241929]. In a mammalian cell fusion assay, HAP2P acts as an authentic fusogen requiring expression on both fusing cells, resembling the bidirectional mechanism of C. elegans somatic fusogens [PMID:36241929]. Its protein levels are set upstream by the PfDPL–PfGID E3 ubiquitin ligase axis: deletion of PfDPL significantly decreases HAP2P protein at gametocyte days 6 and 12, placing HAP2P downstream of this regulatory pathway during gametocyte development [PMID:41986327]. Beyond these findings, no structural model or direct binding partners of HAP2P itself have been characterized in the available corpus.","teleology":[{"year":2022,"claim":"Establishing where and when HAP2P acts was needed to connect it to a specific developmental event; localizing it to stage V gametocytes and the male microgamete flagellum placed it at the male fertilization interface.","evidence":"Immunofluorescence and subcellular localization in stage V gametocytes and male microgametes of P. falciparum","pmids":["36241929"],"confidence":"Medium","gaps":["Does not resolve the topology or membrane orientation of HAP2P within the flagellar membrane","No timing data on when HAP2P first appears relative to microgamete activation"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"claim":"Whether HAP2P was functionally required or redundant with its paralog was unknown; individual deletion showed it is essential and non-redundant for male fertility and mosquito transmission.","evidence":"Gene deletion analysis with genetic crosses and mosquito transmission assays in P. falciparum","pmids":["36241929"],"confidence":"High","gaps":["Does not define the molecular step (docking vs merger) at which fertility fails","Does not clarify why the paralog PfHAP2 cannot compensate despite family relationship"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2022,"claim":"The essentiality phenotype did not prove a fusogenic mechanism; a heterologous cell fusion assay demonstrated HAP2P is an authentic fusogen requiring expression on both fusing cells.","evidence":"Mammalian cell fusion assay with PfHAP2 and HAP2P expressed on fusing cells","pmids":["36241929"],"confidence":"Medium","gaps":["Single method (cell fusion assay) without biochemical reconstitution of membrane merger","The distinct contributions of HAP2P versus the co-expressed PfHAP2 in the assay are not separated"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":2026,"claim":"How HAP2P abundance is controlled during gametocyte maturation was unaddressed; quantitative proteomics placed HAP2P downstream of the PfDPL–PfGID E3 ubiquitin ligase axis.","evidence":"Quantitative proteomics of ΔPfDPL gametocytes versus parental controls at days 6 and 12 in P. falciparum","pmids":["41986327"],"confidence":"Medium","gaps":["Does not establish whether HAP2P is a direct ubiquitination substrate or is regulated indirectly","Does not identify the transcriptional versus post-translational basis of the abundance change"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]},{"year":null,"claim":"A direct structure of HAP2P and identification of its fusion-triggering partners or conformational mechanism remain unknown.","evidence":"","pmids":[],"confidence":"Low","gaps":["No experimental structure of HAP2P itself exists in the corpus (existing structural data concern the PfHAP2 paralog's domain 3)","The trigger and conformational cycle that drives HAP2P-mediated membrane merger are uncharacterized","No direct binding partners on the female gamete surface identified"],"attribution":[{"species":"Plasmodium falciparum","strain":""}]}],"mechanism_profile":{"molecular_activity":[],"localization":[],"pathway":[],"complexes":[],"partners":["PFHAP2 (PARALOG, CO-EXPRESSED IN CELL FUSION ASSAY) [#2]","PFDPL (UPSTREAM REGULATOR OF HAP2P PROTEIN LEVELS) [#3]"],"other_free_text":["Essential and non-redundant for male gamete fertility and mosquito transmission in P. falciparum [#1]","Acts as a bidirectional fusogen requiring expression on both fusing cells, analogous to C. elegans somatic fusogens [#2]","Protein abundance regulated downstream of the PfDPL–PfGID E3 ubiquitin ligase axis during gametocyte development [#3]","Crystallographic structural data in the corpus pertain to the PfHAP2 paralog domain 3, not to HAP2P (PF3D7_0816300) itself [#4]"]}},"prefetch_data":{},"corpus_meta":[{"pmid":"36241929","id":"PMC_36241929","title":"Malaria parasites utilize two essential plasma membrane fusogens for gamete fertilization.","date":"2022","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/36241929","citation_count":20,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["PfHAP2P"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41498187","id":"","title":"Crystal structure and nanobodies against domain 3 of the malaria parasite fusogen Plasmodium falciparum HAP2.","date":"2026","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/41498187","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HAP2P"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"41986327","id":"","title":"GID/CTLH E3 ligase complex control cell fate programs for sexual development of Plasmodium falciparum.","date":"2026","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/41986327","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HAP2P"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"40163471","id":"","title":"Advances in the dissection of Anopheles-Plasmodium interactions.","date":"2025","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/40163471","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HAP2P"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"36685595","id":"","title":"Host-parasite interactions during Plasmodium infection: Implications for immunotherapies.","date":"2023","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/36685595","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HAP2P"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false},{"pmid":"37711230","id":"","title":"Transcriptomic approaches for identifying potential transmission blocking vaccine candidates in Plasmodium falciparum: a review of current knowledge and future directions.","date":"2023","source":"3 Biotech","url":"https://pubmed.ncbi.nlm.nih.gov/37711230","citation_count":0,"is_preprint":false,"source_species":["Pf"],"role":"primary","match_terms":["HAP2P"],"competing_organism_flag":false,"competing_organism_match":"","competing_organism_only":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7812,"output_tokens":1432,"usd":0.022458,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":6388,"output_tokens":2311,"usd":0.044858,"stage2_stop_reason":"end_turn"},"total_usd":0.067316,"stage1_batch_id":"msgbatch_01NE1MTa8x1hW7Lo4tAaNzY1","stage2_batch_id":"msgbatch_0141vaQdeFvbo2q39AinvXM9","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2022,\n      \"finding\": \"HAP2P (PfHAP2p / PF3D7_0816300) is expressed in stage V gametocytes and localizes throughout the flagellum of male gametes in P. falciparum.\",\n      \"method\": \"Immunofluorescence / subcellular localization experiments in stage V gametocytes and male microgametes\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization experiment with functional context (flagellar localization tied to fusion role), single lab, two orthogonal methods (localization + gene deletion)\",\n      \"pmids\": [\"36241929\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"Gene deletion of HAP2P (PF3D7_0816300) individually abolishes male fertility and prevents parasite transmission to the mosquito, establishing a non-redundant essential role distinct from the paralog PfHAP2.\",\n      \"method\": \"Gene deletion analysis and genetic crosses with mosquito transmission assays\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean knockout with defined phenotype (loss of male fertility and transmission), replicated across two independent gene deletions (HAP2P and HAP2) with genetic crosses confirming non-redundancy\",\n      \"pmids\": [\"36241929\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"HAP2P (PF3D7_0816300) functions as an authentic plasma membrane fusogen: using a cell fusion assay, it was demonstrated that HAP2P (together with PfHAP2) is required on both fusing cells for successful fusion, resembling the bidirectional mechanism of C. elegans somatic fusogens.\",\n      \"method\": \"Mammalian cell fusion assay with expression of PfHAP2 and PfHAP2p on fusing cells\",\n      \"journal\": \"Cellular and molecular life sciences : CMLS\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct cell fusion assay establishing fusogen activity, single lab, single method (cell fusion assay)\",\n      \"pmids\": [\"36241929\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The protein levels of HAP2P (PF3D7_0816300) are regulated downstream of PfDPL (a cryptochrome-like protein controlled by the PfGID E3 ubiquitin ligase complex): deletion of PfDPL causes a significant decrease in HAP2P protein levels at gametocyte days 6 and 12.\",\n      \"method\": \"Quantitative proteomics of ΔPfDPL gametocytes compared to parental controls at days 6 and 12\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — quantitative proteomics with genetic knockout establishing pathway placement of HAP2P downstream of PfDPL, single lab\",\n      \"pmids\": [\"41986327\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"The crystal structure of domain 3 of PfHAP2 (the cognate domain in the related PfHAP2 paralog, not PF3D7_0816300 itself) was determined in complex with a nanobody; nanobodies binding domain 3 of PfHAP2 with nanomolar affinity were identified, with some cross-species reactivity to other Plasmodium HAP2 proteins. NOTE: This structural result pertains to PfHAP2 (the paralog), not to HAP2P (PF3D7_0816300) directly.\",\n      \"method\": \"X-ray crystallography of nanobody–PfHAP2 domain 3 complex; affinity measurements\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structure is high quality but concerns the PfHAP2 paralog's domain 3, not PF3D7_0816300; relevance to HAP2P is only indirect (same family); excluded from core model\",\n      \"pmids\": [\"41498187\"],\n      \"is_preprint\": false,\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"current_model\": \"HAP2P (PF3D7_0816300) is an essential, non-redundant plasma membrane fusogen expressed in P. falciparum stage V gametocytes and localized throughout the flagellum of male microgametes; genetic deletion abolishes male fertility and mosquito transmission, and cell fusion assays demonstrate it acts as an authentic fusogen requiring expression on both fusing cells, while its protein levels are regulated upstream by the PfDPL–PfGID E3 ubiquitin ligase axis during gametocyte development.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"HAP2P (PF3D7_0816300) is an essential, non-redundant plasma membrane fusogen that mediates male gamete fusion during the sexual stage of Plasmodium falciparum development [#1, #2]. It is expressed in stage V gametocytes and localizes throughout the flagellum of male microgametes [#0]. Individual gene deletion of HAP2P abolishes male fertility and blocks parasite transmission to the mosquito, establishing a role that cannot be compensated by its paralog PfHAP2 [#1]. In a mammalian cell fusion assay, HAP2P acts as an authentic fusogen requiring expression on both fusing cells, resembling the bidirectional mechanism of C. elegans somatic fusogens [#2]. Its protein levels are set upstream by the PfDPL–PfGID E3 ubiquitin ligase axis: deletion of PfDPL significantly decreases HAP2P protein at gametocyte days 6 and 12, placing HAP2P downstream of this regulatory pathway during gametocyte development [#3]. Beyond these findings, no structural model or direct binding partners of HAP2P itself have been characterized in the available corpus.\",\n  \"teleology\": [\n    {\n      \"year\": 2022,\n      \"claim\": \"Establishing where and when HAP2P acts was needed to connect it to a specific developmental event; localizing it to stage V gametocytes and the male microgamete flagellum placed it at the male fertilization interface.\",\n      \"evidence\": \"Immunofluorescence and subcellular localization in stage V gametocytes and male microgametes of P. falciparum\",\n      \"pmids\": [\"36241929\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Does not resolve the topology or membrane orientation of HAP2P within the flagellar membrane\", \"No timing data on when HAP2P first appears relative to microgamete activation\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Whether HAP2P was functionally required or redundant with its paralog was unknown; individual deletion showed it is essential and non-redundant for male fertility and mosquito transmission.\",\n      \"evidence\": \"Gene deletion analysis with genetic crosses and mosquito transmission assays in P. falciparum\",\n      \"pmids\": [\"36241929\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Does not define the molecular step (docking vs merger) at which fertility fails\", \"Does not clarify why the paralog PfHAP2 cannot compensate despite family relationship\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"The essentiality phenotype did not prove a fusogenic mechanism; a heterologous cell fusion assay demonstrated HAP2P is an authentic fusogen requiring expression on both fusing cells.\",\n      \"evidence\": \"Mammalian cell fusion assay with PfHAP2 and HAP2P expressed on fusing cells\",\n      \"pmids\": [\"36241929\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single method (cell fusion assay) without biochemical reconstitution of membrane merger\", \"The distinct contributions of HAP2P versus the co-expressed PfHAP2 in the assay are not separated\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"How HAP2P abundance is controlled during gametocyte maturation was unaddressed; quantitative proteomics placed HAP2P downstream of the PfDPL–PfGID E3 ubiquitin ligase axis.\",\n      \"evidence\": \"Quantitative proteomics of ΔPfDPL gametocytes versus parental controls at days 6 and 12 in P. falciparum\",\n      \"pmids\": [\"41986327\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Does not establish whether HAP2P is a direct ubiquitination substrate or is regulated indirectly\", \"Does not identify the transcriptional versus post-translational basis of the abundance change\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"A direct structure of HAP2P and identification of its fusion-triggering partners or conformational mechanism remain unknown.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No experimental structure of HAP2P itself exists in the corpus (existing structural data concern the PfHAP2 paralog's domain 3)\", \"The trigger and conformational cycle that drives HAP2P-mediated membrane merger are uncharacterized\", \"No direct binding partners on the female gamete surface identified\"],\n      \"attribution\": [{\"species\": \"Plasmodium falciparum\", \"strain\": \"\"}]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [2]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005886\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"GO:0031514\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"GO:0007342\", \"supporting_discovery_ids\": [1, 2]},\n      {\"term_id\": \"GO:0009566\", \"supporting_discovery_ids\": [1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"PfHAP2 (paralog, co-expressed in cell fusion assay) [#2]\",\n      \"PfDPL (upstream regulator of HAP2P protein levels) [#3]\"\n    ],\n    \"other_free_text\": [\n      \"Essential and non-redundant for male gamete fertility and mosquito transmission in P. falciparum [#1]\",\n      \"Acts as a bidirectional fusogen requiring expression on both fusing cells, analogous to C. elegans somatic fusogens [#2]\",\n      \"Protein abundance regulated downstream of the PfDPL–PfGID E3 ubiquitin ligase axis during gametocyte development [#3]\",\n      \"Crystallographic structural data in the corpus pertain to the PfHAP2 paralog domain 3, not to HAP2P (PF3D7_0816300) itself [#4]\"\n    ]\n  }\n}","audit_flag":null,"strains":[{"strain":"Pf3D7","gene_id":"PF3D7_0816300","name":null,"product":"male gamete fusion factor HAP2P","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PbANKA","gene_id":"PBANKA_0714500","name":null,"product":"HAP2-GCS1 domain-containing protein, putative","uniprot_acc":null,"chromosome":null,"start_pos":null},{"strain":"PkH","gene_id":"PKNH_0504100","name":null,"product":"HAP2-GCS1 domain-containing protein, putative","uniprot_acc":null,"chromosome":null,"start_pos":null}],"gene_symbol":"HAP2P","evaluation":null}