title: Heme binding to the histidine-rich protein II from Plasmodium falciparum.
abstract: The histidine-rich protein II (HRP II) from Plasmodium falciparum has been implicated in the formation of hemozoin, a detoxified, crystalline form of ferric protoporphyrin IX (Fe(3+)-PPIX) produced by the parasite. Fe(3+)-PPIX titrations coupled with quantitative amino acid analysis showed that HRP II binds 15 Fe(3+)-PPIX molecules per 30 kDa monomer. Circular dichroism spectroscopy was used to probe the secondary structure of HRP II with and without bound Fe(3+)-PPIX. These studies have revealed large changes in the secondary structure with Fe(3+)-PPIX binding, changing from a random coil in the absence of Fe(3+)-PPIX to a more ordered helical structure in the presence of Fe(3+)-PPIX. The Fe(3+)-PPIX-bound HRP II structure most closely resembles a 3(10)-helix. Coincident with this structural change caused by Fe(3+)-PPIX binding, the formation of an intermolecular disulfide bond occurs between HRP II monomers. In vitro pull-down assays show an interaction between monomers that is dependent on the presence of Fe(3+)-PPIX. One model that best fits with the data reported here requires formation of 15 intermolecular bishistidyl ligated Fe(3+)-PPIX molecules arranged in a head to head fashion, which would then allow for the formation of an intermolecular disulfide bond. The structure best able to accommodate these requirements is a 3(10)-helix.
authors.affiliation: Department of Chemistry, University of California, Berkeley, Berkeley, California 94720-1460, USA.
authors.forename: Eric L
authors.initials: EL
authors.lastname: Schneider
authors.forename: Michael A
authors.initials: MA
authors.lastname: Marletta
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002942:Circular Dichroism; D017931:DNA Primers; D004220:Disulfides / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D006418:Heme / Q000378:metabolism*; D006860:Hydrogen Bonding; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D000099053:Histidine-Rich Glycoprotein
chemical_list: D017931:DNA Primers; D004220:Disulfides; D011506:Proteins; D000099053:Histidine-Rich Glycoprotein; D006418:Heme