New Insights into Hemopexin-Binding to Hemin and Hemoglobin

Abstract

Hemopexin (Hx) is a plasma glycoprotein that scavenges heme (Fe(III) protoporphyrin IX). Hx has important implications in hemolytic disorders and hemorrhagic conditions because releasing hemoglobin increases the labile heme, which is potentially toxic, thus producing oxidative stress. Therefore, Hx has been considered for therapeutic use and diagnostics. In this work, we analyzed and mapped the interaction sequences of Hx with hemin and hemoglobin. The spot-synthesis technique was used to map human hemopexin (P02790) binding to hemin and human hemoglobin. A library of 15 amino acid peptides with a 10-amino acid overlap was designed to represent the entire coding region (aa 1-462) of hemopexin and synthesized onto cellulose membranes. An in silico approach was taken to analyze the amino acid frequency in the identified interaction regions, and molecular docking was applied to assess the protein-protein interaction. Seven linear peptide sequences in Hx were identified to bind hemin (H1–H7), and five were described for Hb (Hb1–Hb5) interaction, with just two sequences shared between hemin and Hb. The amino acid composition of the identified sequences demonstrated that histidine residues are relevant for heme binding. H105, H293, H373, H400, H429, and H462 were distributed in the H1–H7 peptide sequences, but other residues may also play an important role. Molecular docking analysis demonstrated Hx’s association with the β-chain of Hb, with several hotspot amino acids that coordinated the interaction. This study provides new insights into Hx-hemin binding motifs and protein-protein interactions with Hb. The identified binding sequences and specific peptides can be used for therapeutic purposes and diagnostics as hemopexin is under investigation to treat different diseases and there is an urgent need for diagnostics using labile heme when monitoring hemolysis.

The Search for Associations of Serum Proteins with the Presence of Unstable Atherosclerotic Plaque in Coronary Atherosclerosis

“…Hemopexin binds hemoglobin and free heme of erythrocytes and suppresses excessive oxidative activity. The concentration of this protein increases several times during inflammation, and it is also referred to as acute phase glycoproteins [ 10 , 11 ]. The concentration of hemopexin protein in the blood significantly differed in the study groups, and in group 2 (Ns) it was 11% less than in group 1 (St) ( Table 1 ).…”

Altered Expression of Two Small Secreted Proteins (ssp4 and ssp6) Affects the Degradation of a Natural Lignocellulosic Substrate by Pleurotus ostreatus

“…One of these is hemopexin, (id 133592), which encodes for a protein that exhibits hemin-binding properties and has been designated ostreopexin in P. ostreatus [39]. While its role in lignin degradation has not been investigated, it is conceivable that it may be involved in transferring heme to ligninolytic peroxidases in a similar manner as hemin and hemoglobin [40,41]. Alternatively, it may serve as an ROS scavenger involved in protecting the cell from oxidative damage [42].…”