title: Haptoglobin-related protein is a high-affinity hemoglobin-binding plasma protein.
abstract: Haptoglobin-related protein (Hpr) is a primate-specific plasma protein associated with apolipoprotein L-I (apoL-I)-containing high-density lipoprotein (HDL) particles shown to be a part of the innate immune defense. Despite the assumption hitherto that Hpr does not bind to hemoglobin, the present study revealed that recombinant Hpr binds hemoglobin as efficiently as haptoglobin (Hp). However, in contrast to Hp, Hpr did not promote any high-affinity binding to the scavenger receptor CD163. Binding of hemoglobin to circulating native Hpr incorporated into the HDL fraction was indicated by hemoglobin-affinity precipitation of plasma Hpr together with apoL-I. In conclusion, plasma has 2 high-affinity hemoglobin-binding haptoglobins instead of one, but only Hp-hemoglobin complexes are efficiently recognized by CD163. Circulating Hpr-bound hemoglobin should therefore be taken into consideration when measuring "free" plasma hemoglobin. Furthermore, Hpr-bound hemoglobin might contribute to the biologic activity of the circulating apoL-I/Hpr-containing HDL particles.
authors.affiliation: Department of Medical Biochemistry, University of Aarhus, DK-8000 Aarhus C, Denmark.
authors.forename: Marianne Jensby
authors.initials: MJ
authors.lastname: Nielsen
authors.forename: Steen Vang
authors.initials: SV
authors.lastname: Petersen
authors.forename: Christian
authors.initials: C
authors.lastname: Jacobsen
authors.forename: Claus
authors.initials: C
authors.lastname: Oxvig
authors.forename: David
authors.initials: D
authors.lastname: Rees
authors.forename: Holger Jon
authors.initials: HJ
authors.lastname: Møller
authors.forename: Søren Kragh
authors.initials: SK
authors.lastname: Moestrup
mesh_terms: D000595:Amino Acid Sequence; D000951:Antigens, Neoplasm / Q000235:genetics / Q000378:metabolism*; D001798:Blood Proteins / Q000235:genetics / Q000378:metabolism*; D002846:Chromatography, Affinity; D006242:Haptoglobins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020349:Surface Plasmon Resonance
chemical_list: D000951:Antigens, Neoplasm; D001798:Blood Proteins; C485359:HP protein, human; C058632:HPR protein, human; D006242:Haptoglobins; D006454:Hemoglobins; D011994:Recombinant Proteins