Haptoglobin evolution: polymeric forms of Hp in the Bovidae and Cervidae families

Molecular Characterization of Buffalo Haptoglobin: Sequence Based Structural Comparison Indicates Convergent Evolution Between Ruminants and Human

Haptoglobin (Hp) protein has high affinity for hemoglobin (Hb) binding during intravascular hemolysis and scavenges the hemoglobin induced free radicals. Earlier reports indicate about uniqueness of Hp molecule in human and cattle, but in other animals, it is not much studied. In this paper, we characterized buffalo Hp molecule and determined its molecular structure, evolutionary importance, and tissue expression. Comparative analysis and predicted domain structure indicated that the buffalo Hp has an internal duplicated region in α-chain only similar to an alternate Hp2 allele in human. This duplicated part encoded for an extra complement control protein CCP domain. Phylogenetic analysis revealed that buffalo and other ruminants were found to group together separated from all other non-ruminants, including human. The key amino acid residues involved in Hp and Hb as well as Hp and macrophage scavenger receptor, CD163 interactions in buffalo, depicted a significant variation in comparison to other non-ruminant species. Constitutive expression of Hp was also confirmed across all the vital tissues of buffalo, for the first time. Results revealed that buffalo Hp is both structurally and functionally conserved, having internal duplication in α-chain similar to human Hp2 and other ruminant species, which might have evolved separately as a convergent evolutionary process. Furthermore, the presence of extra Hp CCP domain possibly in all ruminants may have an effect during dimerization of molecule in these species.

Evolutionary aspects of hemoglobin scavengers

With the evolution of fish, systems appeared for the disposal of the hemoglobin (Hb) that was inevitably released from erythrocytes. Thus, a plasma protein that bound free Hb with great affinity, haptoglobin (Hp), evolved from a protease of the innate immune system. In parallel, other proteins appeared (for example, hemopexin and alpha(1)-microglobulin), which bound and mediated the removal of free heme groups. Remarkably, Hp later disappeared in some vertebrate lineages, suggesting that it could also be disadvantageous. In the avian lineage, a soluble protein evolved, possibly from a scavenger receptor, which in some birds seems to have replaced Hp. Among mammals, multimeric forms of Hp appeared independently at two discrete times, suggesting that this form of the protein confers an advantage on the bearer, possibly by improving resistance to infection.

Determination of Haptoglobin in Bovine Serum using Polyclonal and Monoclonal Anti-human Haptoglobin Antibodies

Two ELISA procedures to determine haptoglobin (Hp) in bovine serum were developed. Equine haemoglobin was used as the solid phase. Self-developed goat polyclonal antibody (variant I) and monoclonal antibody (variant II) raised against human Hp were used. The results were compared with the guaiacol method. High correlation was found (r = 0.96 and r = 0.90, respectively) based on the results of 548 bovine serum samples, of which 357 were from clinically healthy cows and 191 from cows and calves monitored during treatment for the most common diseases. The Hp detection limit of ELISA using polyclonal Ab was 0.1 mg/l and using MoAb 0.21 mg/l. The addition of 2% PEG 6000 at the antibody-binding steps enabled major shortening of the incubation periods. The relatively short time, low cost of reagents, and high correlation with the reference method support the use of these ELISA variants in bovine diagnostics.

Identification of acute phase proteins and assays applicable in nondomesticated mammals

The serum concentration of acute phase proteins (APPs) increases dramatically in response to inflammation and tissue injury. APPs are clinically useful in a range of domesticated mammals; however, knowledge is limited in nondomesticated mammals. The detective ability of two assays for each of three potential APPs--serum amyloid A (SAA), C-reactive protein (CRP), and haptoglobin (Hp)--was evaluated in eight species. For SAA, a turbidimetric immunoassay (TIA) demonstrated significant detective abilities in the Asian elephant (Elaphas maximus), impala (Aepyceros melampus), musk ox (Ovibos moschatus), and chimpanzee (Pan troglodytes), as did an SAA enzyme-linked immunosorbent assay (ELISA) in the impala. For CRP, both TIA and ELISA had significant detective abilities in the chimpanzee. For Hp, a colorimetric assay demonstrated significant detective abilities in impala, musk ox, sitatunga (Tragelaphus spekeii), and chimpanzee, as did the Hp ELISA in the impala, musk ox, and sitatunga. In conclusion, these results suggest that assays for detection of relevant APPs in several nondomesticated animals are available.

Purification of human haptoglobin 1-1, 2-1, and 2-2 using monoclonal antibody affinity chromatography

Similar to blood type, human plasma haptoglobin (Hp) is classified as 3 phenotypes: Hp 1-1, 2-1, or 2-2. The structural and functional relationship between the phenotypes, however, has not been studied in detail due to the complicated and difficult isolation procedures. This report provides a simple protocol that can be used to purify each Hp phenotype. Plasma was first passed through an affinity column coupled with a high affinity Hp monoclonal antibody. The bound material was washed with a buffer containing 0.2M NaCl and 0.02 M phosphate, pH 7.4, eluted at pH 11, and collected in tubes containing 1M Tris-HCl, pH 6.8. The crude Hp fraction was then chromatographed on a HPLC Superose 12 column in 0.05 M ammonium bicarbonate at a flow rate of 0.5 ml/min. The homogeneity of purified Hp 1-1, 2-1, or 2-2 was greater than 95% as judged by SDS-polyacrylamide gel electrophoresis. Essentially, each Hp isolated was not contaminated with hemoglobin and apolipoprotein A-I as that reported from the other methods, and was able to bind hemoglobin. Neuraminidase treatment demonstrated that the purified Hp possessed a carbohydrate moiety, while Western blot analysis confirmed alpha and beta chains corresponding to each Hp 1-1, 2-1, and 2-2 phenotype. The procedures described here represent a significant improvement in current purification methods for the isolation of Hp phenotypes. Circular dichroic spectra showed that the alpha-helical content of Hp 1-1 (29%) was higher than that of Hp 2-1 (22%), and 2-2 (21%). The structural difference with respect to its clinical relevance is discussed.

Validation of human haptoglobin immunoturbidimetric assay for detection of haptoglobin in equine and canine serum and plasma

The Incstar(R) SPQ II human haptoglobin (Hpt) (Incstar Corporation, Stillwater, MN) immunoturbidimetric assay was validated for the determination of serum and plasma Hpt concentrations in dogs and horses. The anti-human Hpt antiserum supplied with the assay, displayed monospecificity to both dog and horse serum Hpt by immunoelectrophoresis and Western blotting techniques. The automated immunoturbidimetric assay results correlated well with the cyanmethemoglobin binding assay (r=0.953 for canine serum and r=0.941 for equine serum), and had excellent precision at both high and low serum Hpt concentrations (within run and between run coefficients of variation near or less than 5%). The assay was linear in both species by serial dilution of pooled-high serum with pooled-low serum, saline and with Hpt-free serum. Interference from hemolysis (> 25 mg/dl hemoglobin) and lipemia greater than 100 mg/dl caused a false decrease and false increase respectively in Hpt yield with the immunoturbidimetric assay. The anti-Hpt antibody supplied with the assay kit, once diluted with polymer diluent and stored at 4 degrees C, was stable for up to 6 days and gave consistent results.

Cross reactivities among some mammalian haptoglobins studied by a monoclonal antibody

Mouse monoclonal antibody antihuman-Hp, product of clone 2.36.71.41 was found to recognize, however, with different affinities, the immunological determinant on haptoglobin of some mammals (goat, sheep, cow, horse, rabbit). The following differences in immunological cross reactivities were noticed: (i) haptoglobins present in sera of goat, sheep and cow (Artiodactyla, Bovidae) react in enzyme-linked immunosorbent assay (ELISA) and form precipitates in agarose gel; (ii) horse (Perissodactyla) and rabbit (Lagomorpha) haptoglobins react in ELISA, but they do not form precipitates; and (iii) haptoglobins of dog, fox, cat (Carnivora) and pig (Artiodactyla, Suidae) are not recognized by the tested monoclonal antibody either in ELISA or in agarose gel. This study suggests that monoclonal antibody, clone 2.36.71.41, recognizes the structure on haptoglobin around the disulphide bond linking two alpha chains. Antigenic structure of Bovidae haptoglobins is rather similar to human haptoglobin 2-2 (circular polymers) than to 2-1 type (linear polymers). Monoclonal antibody 2.36.71.41 could be used for classification of mammalian haptoglobins by epitope structure. It can distinguish polymeric haptoglobins similar to human type 2-2 from other mammalian haptoglobins.

Haptoglobin in Carnivora: a unique molecular structure in bear, cat and dog haptoglobins

Haptoglobin (Hp), a hemoglobin-binding protein in plasma, consists of alpha and beta subunits and has a tetra-chain arrangement (beta-alpha-alpha-beta) connected by disulfide bridges in most mammals so far examined. Dog Hp has been reported to be unique compared with other Hps in respect that (1) the two alpha beta units are joined by a non-covalent interaction rather than a disulfide bridge and (2) the alpha chain has an oligosaccharide-binding sequence (Asn-X-Ser/Thr) and is glycosylated. To determine whether the unique structures of dog Hp are common in the Carnivora, we purified Hps from sera of bear and cat, and analyzed their subunit structure and partial amino acid sequences. The analyses by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, under both reducing and non-reducing conditions, revealed that bear and cat Hps have similar subunit arrangements to dog Hp, suggesting the absence of a disulfide bridge between two alpha chains. This was confirmed by amino acid sequence analysis of the alpha chains: that is, Cys15 participating in the inter-alpha chain disulfide bridge was replaced by Val in bear or Leu in cat and dog. Thus, the unique subunit arrangement of Hp reported in dog may be common in the Carnivora. In contrast to dog Hp, however, alpha chains of bear and cat Hps were found not to have the typical oligosaccharide binding sequence on their alpha chains and were not glycosylated.

Monoclonal antibody to human haptoglobin reacts with goat haptoglobin

1. Monoclonal antibody 2.36.71.41 produced to human haptoglobin forms precipitates with goat haptoglobin in double immunodiffusion and electroimmunodiffusion. 2. Solid-phase immunoenzymatic assay (ELISA) based on the reaction of the monoclonal antibody 2.36.71.41 with goat haptoglobin can be used for quantitative estimation of haptoglobin content in goat sera. 3. The minimum detectable concentration of goat haptoglobin is 0.03 micrograms/ml.

Plasma haptoglobin in cattle (Bos taurus) exists as polymers in association with albumin

1. Plasma haptoglobin (Hp) in cattle (Bos taurus) has a molecular mass so large that it is virtually unable to penetrate 4% polyacrylamide gels and is excluded from gel filtration media with an upper exclusion limit of greater than 1000 kDa. 2. In most species, apart from ruminants, Hp has a molecular mass of 100 kDa, consisting of two subunits of 40 kDa and two subunits of 9 kDa, although in a few species, such as man, a genetic variant of Hp forms polymers of higher mass. 3. Bovine Hp was purified by (i) salt precipitation, gel filtration and ion exchange chromatography and (ii) by affinity chromatography and gel filtration, with final purification by (iii) preparative electrophoresis. 4. Bovine Hp could only penetrate sodium dodecyl sulphate polyacrylamide gels following denaturation with mercaptoethanol, when it was shown to be composed of subunits of 40 and 16 kDa, but a protein of 67 kDa was consistently present. 5. Western blotting identified the 67 kDa protein as bovine serum albumin. 6. The polymeric form of Hp found in bovine plasma is formed by association of 40 and 16 kDa subunits with albumin.

Bovine and canine acute phase proteins

Acute phase proteins are serum proteins which increase in concentration during the acute phase response to inflammation or infection. The response occurs in all animals, but in different species the response of individual proteins can be significantly different. Of the numerous acute phase proteins which have been identified in humans, a number have been examined in cattle and dogs but usually on an individual basis with little reference to their part in the acute phase response. Biochemical, physiological and clinical investigations into haptoglobin, fibrinogen, alpha 1-proteinase inhibitor, ceruloplasmin, seromucoid and C-reactive protein of cattle and dogs have therefore been reviewed with the emphasis on their role in this response to tissue damage.

Structure and assembly of haptoglobin polymers by electron microscopy

Haptoglobin (Hp) consists of light (L) and heavy (H) chains, the latter of which combine with hemoglobin alpha beta dimers to form a highly stable complex. Human haptoglobin assembles as HL units that occur in two allelic forms; HL1 , which is monovalent, and HL2 , which is divalent. As a result, three phenotypic forms exist in the human population: Hp1-1, the homozygous form in which the monovalent HL1 unit occurs as a dimer; Hp2-2, the homozygous form of the divalent HL2 unit, which gives a series of polymers; and the heterozygous Hp2-1 form, which gives a different series of polymers. We have investigated the structures and assembly properties of these two haptoglobin polymeric series in their complexes with hemoglobin using high-resolution scanning transmission electron microscopy. Polymers of complex are composed of ellipsoidal or bilobal head groups, which are the H alpha beta subunits connected by thin filament-like structures, which are the L chains. Polymers of size up to pentamers can be identified easily by counting the number of head groups in the molecule. Complex 2-1 and complex 2-2 trimers were studied extensively. The differences in detailed morphology show that while the 2-1 trimer is a linear polymer, the 2-2 trimer is a closed circular molecule. The micrograph images suggest that complex 2-2 tetramers and pentamers, and perhaps higher forms may also be cyclic. The structure of the L2 subunit of haptoglobin is shown to be composed of two domains, which may be similar in structure to the single domain of the monovalent L1 chain. The two L2 domains are connected by a hinge that has quite limited flexibility. Using these structural models, assembly characteristics and structural properties of the trimers and tetramers of complex 2-1 and complex 2-2 are described.

Biosynthesis of rabbit haptoglobin: chemical evidence for a single chain precursor

The primary translation product of the mRNA for rabbit haptoglobin was obtained from a rabbit reticulocyte lysate cell-free system by immunoprecipitation with an antiserum that was directed to the beta chain of haptoglobin. Analysis of the translation product by gel electrophoresis and by protein sequencing analysis identified a single polypeptide of Mr 41 000. Sequence analysis established a signal region of 18 residues that was immediately followed by the alpha chain sequence. These results give strong evidence that haptoglobin is initially synthesized as a single chain composed of a signal peptide followed by alpha and beta chain regions, respectively.

Canine haptoglobin: a unique haptoglobin subunit arrangement

1. Isolated canine haptoglobin behaved identically to the alpha 2 beta 2 structure typical of human haptoglobin type 1-1 on alkaline polyacrylamide gel electrophoresis and on gel filtration. 2. In the presence of urea or sodium dodecyl sulphate canine haptoglobin dissociated into alpha beta subunits that separated into alpha and beta chains after reduction with 2-mercaptoethanol. 3. Compositional analysis identified one less half-cystine in canine alpha chain when compared to human alpha 1 chain. 4. These results provide evidence that there is no inter alpha chain disulphide in canine haptoglobin comparable to the alpha 1 20-alpha 1 20 disulphide in human haptoglobin that links the two alpha beta subunits.

Structure and evolution of artiodactyla haptoglobins

1. Artiodactyla haptoglobins (Hps), goat, sheep and cattle (family Bovidae), and pig (family Suidae) were structurally characterized. 2. The polymeric Hp systems of goat, sheep and cattle were similar to the polymeric human Hp system, while the monomeric system of pig was more comparable to the monomeric human form. 3. All members of the Artiodactyla (family Bovidae) examined exhibited a large polypeptide subunit, comparable to that of the beta subunit of human Hp. 4. In addition, a small subunit, similar in molecular weight to the human alpha 2 subunit, was demonstrated. Pig Hp was shown to have two subunits, one slightly larger than the human beta subunit and the other intermediate in size to the human alpha 1 and alpha 2 subunits. 5. Immunoelectrophoretic and immunodiffusion studies indicated complete cross reactivity among the polymeric Artiodactyla Hps. 6. The polymeric Hps do not, however, cross react with the monomeric pig Hp.