title: The heme biosynthesis pathway is essential for Plasmodium falciparum development in mosquito stage but not in blood stages.
abstract: Heme is an essential cofactor for aerobic organisms. Its redox chemistry is central to a variety of biological functions mediated by hemoproteins. In blood stages, malaria parasites consume most of the hemoglobin inside the infected erythrocytes, forming nontoxic hemozoin crystals from large quantities of heme released during digestion. At the same time, the parasites possess a heme de novo biosynthetic pathway. This pathway in the human malaria parasite Plasmodium falciparum has been considered essential and is proposed as a potential drug target. However, we successfully disrupted the first and last genes of the pathway, individually and in combination. These knock-out parasite lines, lacking 5-aminolevulinic acid synthase and/or ferrochelatase (FC), grew normally in blood-stage culture and exhibited no changes in sensitivity to heme-related antimalarial drugs. We developed a sensitive LC-MS/MS assay to monitor stable isotope incorporation into heme from its precursor 5-[(13)C4]aminolevulinic acid, and this assay confirmed that de novo heme synthesis was ablated in FC knock-out parasites. Disrupting the FC gene also caused no defects in gametocyte generation or maturation but resulted in a greater than 70% reduction in male gamete formation and completely prevented oocyst formation in female Anopheles stephensi mosquitoes. Our data demonstrate that the heme biosynthesis pathway is not essential for asexual blood-stage growth of P. falciparum parasites but is required for mosquito transmission. Drug inhibition of pathway activity is therefore unlikely to provide successful antimalarial therapy. These data also suggest the existence of a parasite mechanism for scavenging host heme to meet metabolic needs.
authors.affiliation: From the Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129.
authors.forename: Hangjun
authors.initials: H
authors.lastname: Ke
authors.affiliation: the Department of Molecular Microbiology and the Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Sigala
authors.affiliation: the Laboratory of Malaria and Vector Research, NIAID, National Institutes of Health, Rockville, Maryland 20852, and.
authors.forename: Kazutoyo
authors.initials: K
authors.lastname: Miura
authors.affiliation: From the Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129.
authors.forename: Joanne M
authors.initials: JM
authors.lastname: Morrisey
authors.affiliation: From the Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Mather
authors.affiliation: the Center for Women's Infectious Disease Research and.
authors.forename: Jan R
authors.initials: JR
authors.lastname: Crowley
authors.affiliation: the Center for Women's Infectious Disease Research and Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Jeffrey P
authors.initials: JP
authors.lastname: Henderson
authors.affiliation: the Department of Molecular Microbiology and the Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110, Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Goldberg
authors.affiliation: the Laboratory of Malaria and Vector Research, NIAID, National Institutes of Health, Rockville, Maryland 20852, and.
authors.forename: Carole A
authors.initials: CA
authors.lastname: Long
authors.affiliation: From the Center for Molecular Parasitology, Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19129, avaidya@drexelmed.edu.
authors.forename: Akhil B
authors.initials: AB
authors.lastname: Vaidya
mesh_terms: D000624:5-Aminolevulinate Synthetase / Q000172:deficiency / Q000235:genetics; D000818:Animals; D000852:Anopheles / Q000469:parasitology*; D004912:Erythrocytes / Q000469:parasitology*; D005260:Female; D005294:Ferrochelatase / Q000235:genetics; D055786:Gene Knockout Techniques; D006418:Heme / Q000096:biosynthesis* / Q000378:metabolism; D006801:Humans; D008297:Male; D010963:Plasmodium falciparum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism* / Q000502:physiology; D053719:Tandem Mass Spectrometry
chemical_list: D006418:Heme; D000624:5-Aminolevulinate Synthetase; D005294:Ferrochelatase
keywords: Heme; Insect; Malaria; Mitochondria; Mitochondrial Metabolism