Haptoglobin-related protein is a high-affinity hemoglobin-binding plasma protein.
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.
Nielsen
Marianne Jensby
MJ
Department of Medical Biochemistry, University of Aarhus, DK-8000 Aarhus C, Denmark.
Petersen
Steen Vang
SV
Jacobsen
Christian
C
Oxvig
Claus
C
Rees
David
D
Møller
Holger Jon
HJ
Moestrup
Søren Kragh
SK
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
D000951:Antigens, Neoplasm; D001798:Blood Proteins; C485359:HP protein, human; C058632:HPR protein, human; D006242:Haptoglobins; D006454:Hemoglobins; D011994:Recombinant Proteins