title: Spectroscopic characterization of the heme-binding sites in Plasmodium falciparum histidine-rich protein 2.
abstract: Proteolysis of hemoglobin provides an essential nutrient source for the malaria parasite Plasmodium falciparum during the intraerythrocytic stage of the parasite's lifecycle. Detoxification of the liberated heme occurs through a unique heme polymerization pathway, leading to the formation of hemozoin. Heme polymerization has been demonstrated in the presence of P. falciparum histidine-rich protein 2 (PfHRP2) [Sullivan, D. J., Gluzman, I. Y., and Goldberg, D. E. (1996) Science 271, 219-221]; however, the molecular role that PfHRP2 plays in this polymerization is currently unknown. PfHRP2 is a 30 kDa protein composed of several His-His-Ala-His-His-Ala-Ala-Asp repeats and is present in the parasite food vacuole, the site of hemoglobin degradation and heme polymerization. We found that, at pH 7.0, PfHRP2 forms a saturable complex with heme, with a PfHRP2 to heme stoichiometry of 1:50. Spectroscopic characterization of heme binding by electronic absorption, resonance Raman, and EPR has shown that bound hemes share remarkably similar heme environments as >95% of all bound hemes are six-coordinate, low-spin, and bis-histidyl ligated. The PfHRP2-ferric heme complex at pH 5.5 (pH of the food vacuole) has the same heme spin state and coordination as observed at pH 7.0; however, polymerization occurs as heme saturation is approached. Therefore, formation of a PfHRP2-heme complex appears to be a requisite step in the formation of hemozoin.
authors.affiliation: Department of Biological Chemistry, Division of Medicinal Chemistry, Howard Hughes Medical Institute, University of Michigan, Ann Arbor 48109-0606, USA.
authors.forename: C Y
authors.initials: CY
authors.lastname: Choi
authors.forename: J F
authors.initials: JF
authors.lastname: Cerda
authors.forename: H A
authors.initials: HA
authors.lastname: Chu
authors.forename: G T
authors.initials: GT
authors.lastname: Babcock
authors.forename: M A
authors.initials: MA
authors.lastname: Marletta
mesh_terms: D000818:Animals; D001665:Binding Sites; D002248:Carbon Monoxide / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005290:Ferric Compounds / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D006639:Histidine / Q000378:metabolism*; D010963:Plasmodium falciparum; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods; D013059:Spectrum Analysis, Raman; D000099053:Histidine-Rich Glycoprotein
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D011506:Proteins; D015800:Protozoan Proteins; D000099053:Histidine-Rich Glycoprotein; D006418:Heme; D006639:Histidine; D002248:Carbon Monoxide