Rat hemopexin. Molecular cloning, primary structural characterization, and analysis of gene expression

Abstract

A full-length hemopexin cDNA was isolated from a rat liver cDNA library and the derived amino acid sequence was obtained. Rat hemopexin shows a 76% amino acid homology with human hemopexin. The amino-terminal domain of rat hemopexin contains two histidine residues that are conserved in the human and rat sequences and are the most likely heme axial ligands. Analogous to human hemopexin, the rat hemopexin consists of 10 internal repeating peptide motifs characteristic of the pexin gene family. A complete conservation of cysteine residues is seen between the human and rat sequences suggesting an identical disulfide bridge structure in both proteins. Our analysis of the primary structure of rat hemopexin reveals characteristics typical for members of the pexin gene family and suggests a conserved evolutionary role for the C-terminal (non-heme-binding) domain of this protein. The full-length rat hemopexin cDNA was used to analyze changes in hemopexin gene expression during development and experimental inflammation. RNA blot analysis showed a single 2.0-kb hemopexin mRNA present in fetal liver at day 14. Hemopexin-specific mRNA was not detected in embryonic or fetal tissues at earlier stages of development and was confined to the liver throughout fetal, newborn, and adult life. The abundance of hemopexin mRNA was found to increase throughout gestation, with a sharp increase in the first postnatal weeks, reaching maximum levels in adult animals. Endotoxin-induced inflammation resulted in a 5-fold increase in hepatic hemopexin mRNA content within 48 h without associated changes in hemopexin transcript size. Adult animals exposed to hyperoxia (95% oxygen) showed a 3-fold increase in hepatic hemopexin mRNA content.(ABSTRACT TRUNCATED AT 250 WORDS)

Complex Role of Hemoglobin and Hemoglobin-Haptoglobin Binding Proteins in Haemophilus influenzae Virulence in the Infant Rat Model of Invasive Infection

“…Changes in hematological values, iron absorption, and regulation of genes involved in iron/heme homeostasis are known to occur with age during infancy in both humans and rats (12,13,32,36,51). Among proteins involved in iron/heme scavenging, plasma haptoglobin levels are very low in newborn human infants and do not reach adult-like levels until approximately 6 months of age (32).…”

Genomic sequences encoding two types of medaka hemopexin-like protein Wap65, and their gene expression profiles in embryos

“…Rat hemopexin transcripts were first detected in liver on day 24 of gestation and rapidly increase during the postnatal period (Nikkila et al, 1991). Chicken hemopexin is found around hatching and increases in 4-day-old chicken to more than 1000-fold over embryonic levels as revealed by electroimmunoassay of serum (Grieninger et al, 1986).…”

“…The highest accumulated levels of Wap65 mRNA have been observed in hepatopancreas and their deduced amino acid sequences resemble those of mammalian hemopexins (Kikuchi et al, 1995(Kikuchi et al, , 1997Kinoshita et al, 2001). Hemopexin is a mammalian plasma glycoprotein that is mainly synthesized in liver, functioning as a scavenger of free heme with a high binding affinity to heme (Altruda et al, 1985;Nikkila et al, 1991;Morgan et al, 1993;Tolosano and Altruda, 2002). Crystal structural analysis of rabbit hemopexin revealed two essential histidine residues that are located at heme binding pockets (Paoli et al, 1999).…”

The occurrence of two types of hemopexin-like protein in medaka and differences in their affinity to heme

“…Comparison of the amino acid sequences of two types of medaka Wap65, mWap65-1 and mWap65-2, with those of fish Wap65s and mammalian hemopexins, including goldfish Wap65 (Kikuchi et al, 1995), carp Wap65 (Kinoshita et al, 2001), rainbow trout hemopexin-like protein (Miot et al, 1996) and hemopexins of rabbit (Morgan et al,. 1993), rat (Nikkilä et al, 1991) and human (Altruda et al, 1985;Takahashi et al, 1985). Amino acids identical to those of mWap65-1 are shown as dots; gaps introduced to maximize the alignment are represented by hyphens.…”