[Hemoglobins of reptiles. Expression of alpha-D-genes in the turtles, Chrysemys picta bellii and Phrynops hilarii (Testudines)]

Side-necked turtle (Pleurodira, Chelonia, reptilia) hemoglobin: cDNA-derived primary structures and X-ray crystal structures of Hb A

Red blood cells of yellow-spotted river turtles (Podocnemis unifilis, Pleurodira, Chelonia, REPTILIA) have two hemoglobin (Hb) components, Hb A and Hb D. We purified the hemoglobin component homologous to amniote (reptiles, birds, and mammals) adult Hb A which comprises two identical α(A) -globin polypeptides and two identical β-globin polypeptides. To establish the crystal structure of Podocnemis Hb A, we first determined the globin primary structures using cDNA nucleotide sequencing with the assistance of protein sequencing. The purified Podocnemis Hb A produced a different form of crystal for each of the two different buffer systems used: form A, tetragonal crystals (space group, P4₁2₁2), produced under neutral pH (pH 7-8) conditions; and form B, hexagonal crystals (space group, P6₁22), produced under high alkaline pH (pH 11-13) conditions. Single crystals of the two forms were examined by Raman microscopy with an excitation of 532 nm, indicating their structural differences. The crystal structures of the two forms were constructed by X-ray crystallographic diffraction at a resolution of 2.20 Å for form A and 2.35 Å for form B. The differences of the tertiary and quaternary structures of the two forms were marginal; however, one clear difference was found in helix structure. When comparing Podocnemis Hb A with Hb A from specimens in other taxa, such as Anser indicus (birds) and Homo sapiens (mammals) by SHELXPRO, the root mean square deviation (RMSD) between the corresponding Cα atoms of the two globins does not exceed 2.0 Å. These low values indicate the crystal structures resemble each other. Our data on X-ray crystal structures and Raman spectra not only reveal the first findings on the two crystal forms of Podocnemis unifilis Hb A but also provide the first refined models for reptilian adult Hb A.

Indefinite noncooperative self-association of chicken deoxy hemoglobin D

The minor tetrameric hemoglobin (Hb), Hb D, of chicken red blood cells self-associates upon deoxygenation. This self-association enhances the cooperativity of oxygen binding. The maximal Hill coefficient is greater than 4 at high Hb concentrations. Previous measurements at low Hb concentrations were consistent with a monomer-to-dimer equilibrium and an association constant of ∼1.3-1.6 × 10(4) M(-1). Here, the Hb tetramer is considered as the monomer. However, new results indicate that the association extends beyond the dimer. We show by combination of Hb oligomer modeling and sedimentation velocity analyses that the data can be well described by an indefinite noncooperative or isodesmic association model. In this model, the deoxy Hb D associates noncooperatively to give a linear oligomeric chain with an equilibrium association constant of 1.42 × 10(4) M(-1) at 20°C for each step. The data are also well described by a monomer-dimer-tetramer equilibrium model with monomer-to-dimer and dimer-to-tetramer association constants of 1.87 and 1.03 × 10(4) M(-1) at 20°C, respectively. A hybrid recombinant Hb D was prepared with recombinant α(D)-globin and native β-globin to give a Hb D tetramer (α(2)(D)β(2)). This rHb D undergoes decreased deoxygenation-dependent self-association compared with the native Hb D. Residue glutamate 138 has previously been proposed to influence intertetramer interactions. Our results with recombinant Hb D show that Glu138 plays no role in deoxy Hb D intertetramer interactions.

Distribution, adaptation and physiological meaning of thiols from vertebrate hemoglobins

In the present review, the sequences of hemoglobins (Hb) of 267 adult vertebrate species belonging to eight major vertebrate taxa are examined for the presence and location of cysteinyl residues in an attempt at correlation with their ecophysiology. Essentially, all vertebrates have surface cysteinyl residues in Hb molecules whereby their thiol groups may become highly reactive. Thiol-rich Hbs may display eight or more thiols per tetramer. In vertebrates so far examined, the cysteinyl residues occur in 44 different sequence positions in alpha chains and 41 positions in beta chains. Most of them are conservatively located and occur in only a few positions in Teleostei, Aves and Mammalia, whereas they are dispersed in Amphibia. The internal cysteinyl residue alpha104 is ubiquitous in vertebrates. Residue beta93 is highly conserved in reptiles, birds and mammals. The number of cysteine residues per tetramer with solvent access varies in vertebrates, mammalians and bony fish having the lowest number of external residues, whereas nearly all external cysteine residues in Aves and Lepidosauria are of the surface crevice type. In cartilaginous fish, amphibians, Crocodylidae and fresh water turtles, a substantial portion of the solvent accessible thiols are of the totally external type. Recent evidence shows that some Hb thiol groups are highly reactive and undergo extensive and reversible S-thiolation, and that they may be implicated in interorgan redox equilibrium processes. Participation of thiol groups in nitric oxide ((*)NO) metabolism has also been proved. The evidence argues for a new physiologically relevant role for Hb via involvement in free radical and antioxidant metabolism.

Functional adaptation and its molecular basis in vertebrate hemoglobins, neuroglobins and cytoglobins

Hemoglobin (Hb), the paradigm for allosteric proteins through decades, has gained renaissance in recent years following discovery of globins or their genes in all living organisms and in all tissues of higher animals, and of new members of the globin family, such as neuroglobins, Ngb, found predominantly in neural and nerve tissues and cytoglobins, Cygb, that has unprecedented nuclear location. The recent progresses in this field have been prompted by the development of sophisticated techniques to probe molecular structure and functions, which have revealed novel functions, such as the scavenging and release of vasoactive nitric oxide and the regulation of cellular metabolism. This review deals with the functional adaptations and the underlying molecular mechanisms in globins and presents case examples of molecular adaptations encountered in vertebrates and agnathans.

Molecular characterization of hemoglobin alpha-D chains from Geochelone carbonaria and Geochelone denticulata land turtles

In order to help elucidate the evolution of alpha-globins, the complete cDNA and amino acid sequences of Geochelone carbonaria and Geochelone denticulata land turtles alpha-D chains have been described. In G. carbonaria, the cDNA is 539 bp with ATG start codon located at position 46, TGA stop codon at position 469 and AATAAA polyadenylation signal at position 520. In G. denticulata, the cDNA is 536 bp with ATG start codon located at position 46, TGA stop codon at position 469 and AATAAA polyadenylation signal at position 517. Both cDNAs codify 141 amino acid residues, differing from each other in only four amino acid residues. When comparing with human Hb alpha-chain, alterations in important regions can be noted: alpha110 Ala-Gly, alpha114 Pro-Gly, alpha117 Phe-Tyr and alpha122 His-Gln. There is a high homology between the amino acids of these turtles when compared with chicken alpha-D chains, progressively decreasing when compared with human, crocodile, snake, frog and fish alpha-chains. Phylogenetic analysis of alpha-D chains shows that those of turtles are closer to those of birds than to snakes and lizards.

The primary structure of three hemoglobin chains from the indigo snake (Drymarchon corais erebennus, Serpentes): first evidence for alphaD chains and two beta chain types in snakes

The hemoglobin of the indigo snake (Drymarchon corais erebennus, Colubrinae) consists of two components, HbA and HbD, in the ratio of 1:1. They differ in both their alpha and beta chains. The amino acid sequences of both a chains (alphaA and alphaD) and one beta chain (betaI) were determined. The presence of an alphaD chain in a snake hemoglobin is described for the first time. A comparison of all snake beta chain sequences revealed the existence of two paralogous beta chain types in snakes as well, which are designated as betaI and betaII type. For the discussion of the physiological properties of Drymarchon hemoglobin, the sequences were compared with those of the human alpha and beta chains and those of the closely related water snake Liophis milians where functional data are available. Among the heme contacts, the substitution alphaD58(E7)His-->Gln is unusual but most likely without any effect. The residues responsible for the main part of the Bohr effect are the same as in mammalian hemoglobins. In each of the three globin chains only two residues at positions involved in the alpha1/beta2 interface contacts, most important for the stability and the properties of the hemoglobin molecule, are substituted with regard to human hemoglobin. On the contrary, nine, eleven, and six alpha1/beta1 contact residues are replaced in the alphaA, alphaD, betaI chains, respectively.

Functional behavior of tortoise hemoglobin Geochelone denticulata

The hemolysate from Geochelone denticulata contains two main hemoglobin components, as shown by ion exchange chromatography and polyacrylamide gel electrophoresis (PAGE). Electrophoresis under dissociating conditions showed three types of globin chains. The apparent molecular mass, as determined by gel filtration on Sephadex G-200, was compatible with tetrameric Hb, which was unable to polymerize. The G. denticulata Hb has a P50 value of 9.56 mm Hg at pH 7.4. The Hb oxygenation appears to be under the control of organic phosphates and hydrogen ion since it is strongly affected by those species. In the presence ATP or IHP the P50 values increased to 29.51 mm Hg and 54.95 mm Hg, respectively, at pH 7.4. The n50 was generally lower than 1.5 in stripped Hb, suggesting a dissociation of tetramers. In the presence of organic phosphates n50 values increased to approximately 2.5. The Bohr effect was evident in oxygen equilibrium experiments. The hematocrit (32%) and Hb concentration (5.7 mM as heme) of G. denticulata blood were substantially larger than those of G. carbonaria, but the methemoglobin levels were similar in both species, approximately 1%. Thus, the oxygen capacity of blood appears to be higher in G. denticulata than in G. carbonaria, particularly considering the functional properties of their Hbs, which would guarantee the survival of animals.

The primary structure of hemoglobin D from the Aldabra giant tortoise, Geochelone gigantea

The complete primary structures of alpha D-2- and beta-globin of hemoglobin D (Hb D) from the Aldabra giant tortoise, Geochelone gigantea, have been constructed by amino acid sequencing analysis in assistance with nucleotide sequencing analysis of PCR fragments amplified using degenerate oligonucleotide primers. Using computer-assisted sequence comparisons, the alpha D-2-globin shared a 92.0% sequence identity versus alpha D-globin of Geochelone carbonaria, a 75.2% versus alpha D-globin of Aves (Rhea americana) and a 62.4% versus alpha A-globin of Hb A expressed in adult red blood cells of Geochelone gigantea. Additionally, judging from their primary structures, an identical beta-globin was common to the two hemoglobin components, Hb A and Hb D. The alpha D-2- and beta-globin genes contained the three-exon and two-intron configurations and showed the characteristic of all functional vertebrate hemoglobin genes except an abnormal GC dinucleotide instead of the invariant GT at the 5' end of the second intron sequence. The introns of alpha D-2-globin gene were both small (224-bp/first intron, 227-bp/second intron) such that they were quite similar to those of adult alpha-type globins; the beta-globin gene has one small intron (approximately 130-bp) and one large intron (approximately 1590-bp). A phylogenetic tree constructed on primary structures of 7 alpha D-globins from Reptilia (4 species of turtles, 2 species of squamates, and 1 species of sphenodontids) and two embryonic alpha-like globins from Aves (Gullus gullus) and Mammals (Homo sapiens) showed the following results: (1) alpha D-globins except those of squamates were clustered, in which Sphenodon punctatus was a closer species to birds than turtles; (2) separation of the alpha A- and alpha D-globin genes occurred approximately 250 million years ago after the embryonic alpha-type globin-genes (pi' and zeta) first split off from the ancestor of alpha-type globin gene family.

Primary structure of hemoglobin from cobra Naja naja naja

Cobra snake Naja naja naja hemoglobin shows four bands on Triton electrophoresis. We present the primary structure of one alpha and one beta chain. The separation of polypeptide chains was achieved by ion exchange chromatography on carboxymethyl cellulose column. The amino acid sequence was established by automatic Edman degradation of the native chains and tryptic and hydrolytic peptides in a gas-phase sequencer. The structural data are compared with those of human and other reptile hemoglobins and reveal not only large variations from human but within reptiles. The amino acid exchanges involve several subunit contacts and heme binding sites. This is the first study on the hemoglobin of a land snake. There are only two amino acid sequences of sea snake hemoglobin (Microcephalophis gracilis gracilis and Liophis miliaris) reported in the literature.

Allosteric transition in hemoglobin (alpha 2A beta 2I) from the rhynchocephalian reptile relict Sphenodon punctatus

The major hemoglobin component Hb A of the tuatara, Sphenodon punctatus, a relict of the rhynochocephalian reptiles that lived 200 million years ago, was investigated in the light of the apparent contradiction inherent in an effect of organic phosphate cofactors on the oxygen affinity of hemoglobins exhibiting hyperbolic oxygen equilibrium curves. The heterotropic allosteric effect of ATP, the major erythrocytic cofactor in the tuatara, is shown to be correlated with distinct homotropic interactions (Hill's cooperativity coefficient at half-saturation, n50, attaining 1.3-1.5 above pH 7.5), and with free energies of heme-heme interaction (4.7 kJ.mole-1 at pH 7.2) which resemble those in other vertebrate hemoglobins that exhibit higher n50 values. Curiously, chloride ions increase hemoglobin-oxygen affinity below pH +/- 7.2. The possible mechanisms underlying the effects of ATP and chloride are discussed.

Hemoglobins of reptiles. The primary structures of the alpha I- and beta I-chains of common iguana (Iguana iguana) hemoglobin

The primary structures of alpha I- and beta I-chains from the hemoglobins of the Common Iguana (Iguana iguana) are presented. The globin chains were separated on CM-cellulose in 8 M urea buffer. The amino-acid sequences were established by automatic Edman degradation of the native chains, the tryptic peptides and a peptide obtained by cyanogen bromide cleavage. The sequences are compared with human hemoglobin. Amino-acid replacements at positions critical for structure and function of the hemoglobin are discussed. The requirements for binding of ATP and also of DPG as allosteric effectors at the beta-chains seem to be fulfilled. Comparison of the alpha-chains with those of the Viper (Vipera aspis) shows 66 amino-acid substitutions. This number is in the same order of magnitude as the ones found by comparison with alpha-chains of crocodiles and mammals as well as with alpha A-chains of a turtle and birds. This result points towards a period of independent evolution of the reptile lines leading to the Common Iguana on one hand and to the Viper on the other. This time span is comparable to the one separating mammals from reptiles.

Primary structure of the hemoglobins from Sphenodon (Sphenodon punctatus, Tuatara, Rynchocephalia). Evidence for the expression of alpha D-gene

Sphenodon is the sole representative of the "beakhead" reptiles which were widely distributed during the Triassic period before the spectacular rise of dinosaurs. Sphenodon punctatus is the only survivor ("living fossil") of this period. The morphological features of Sphenodon are remarkably conservative and differ little from reptiles living 200 million years ago. In the present paper the determination of the primary structure of the tetrameric hemoglobins is described: three components are identified: hemoglobin A' (alpha A2 beta II2), hemoglobin A (alpha A2 beta I2) and hemoglobin D (alpha D2 beta II2). The components were characterized electrophoretically, the four different peptide chains were characterized by Triton electrophoresis as well as by high-performance liquid chromatography. The hemoglobins and--under dissociating conditions--also the chains, were isolated on columns of cellulose ion exchangers. Sequence determination was carried out after cleavage of the individual chains with trypsin and after a specific chemical cleavage of the Asp-Pro bond. For sequence determination the film technique and gas-phase method were employed. The data are compared with the sequence of the human hemoglobin, and interpretations of the amino-acid sequences are given. Particularly notable is the evidence of hemoglobin D: this hemoglobin (alpha D2 beta II2) is found only in birds, and in two cases in turtles. However, this component is not found in other reptiles. The results make possible an interpretation of the relatively high oxygen affinity and explain the lack of cooperativity (myoglobin properties) of these tetrameric hemoglobins.

Structural adaptation of bird hemoglobins to high-altitude respiration and the primary sequences of black-headed gull (Larus ridibundus, Charadriiformes) alpha A- and beta/beta'-chains

Two hemoglobin components HbA (alpha A2 beta 2) and (alpha D2 beta 2) have been detected by analytical electrophoresis in the lysed erythrocytes of the adult Black-Headed Gull (Larus ridibundus). We report the complete primary structure of the alpha A- and beta-chains of the major hemoglobin component HbA. Following the chain separation and isolation of the tryptic peptides by RP-HPLC, the amino-acid sequence was established by automatic Edman degradation in spinning cup and gas-phase sequencers. The primary structures of alpha A- and beta-chains from the Black-Headed Gull HbA differ by 11 and by 6 amino-acid residues from the corresponding chains of Greylag Goose. These changes are randomly distributed over both alpha-helical and interhelical regions. The presence of beta/beta'-chains is indicated by the observation of Ile/Leu at position beta 78. An exchange at position beta 55 (D6)Leu-Asn which is known to be involved in the alpha 1 beta 1-interface with alpha 119(H2)Pro has been found. It is suggested that packing contacts in the alpha 1 beta 1-interface are important for high altitude respiration in birds.

The primary structures of the major and minor hemoglobin-components of adult Andean goose (Chloephaga melanoptera, Anatidae): the mutation Leu----Ser in position 55 of the beta-chains

The primary structures of the hemoglobin components Hb A and Hb D of the adult Andean Goose (Chloephaga melanoptera) are presented. The globin chains were separated on CM-Cellulose in 8M urea buffer. The amino-acid sequences were established by automatic Edman degradation of the globin chains and of the tryptic peptides in liquid- and gas-phase sequenators. The sequences are aligned with those of Greylag Goose (Anser anser) as a biological reference and other sequences of birds. A detailed evaluation of all residues of Andean Goose hemoglobins on the basis of the 12000 known avian globin sequences leads to a molecular pattern for high-altitude respiration of geese. The replacement of functional and structural importance is the unique occurrence of the residue beta 55 Leu----Ser (all other exchanges are functionally neutral), interrupting the same alpha 1 beta 1-interface contact (alpha 119-beta 55) that accounts for high-altitude respiration of the Barheaded Goose (Anser indicus); there the mutation is found on alpha A 119. Loosening the constraints of this interface must be interpreted as a destabilization of the low-affinity T-structure in favour of the high-affinity R-structure. The structural and functional significance of this interface for the molecular biology of high-altitude respiration of the Andean Goose and Barheaded Goose is discussed. Since Hb A consists of alpha A2 beta 2 and Hb D consists of alpha D2 beta 2 the mutation occurring in blood of the Andean Goose affects both hemoglobins whereas in the case of the Barheaded Goose only Hb A is affected. These results show that Hb D can be considered a biological reserve to enlarge situatively the normal hemoglobin function. A general molecular pattern for permanent (selective advantage of high intrinsic oxygen affinity) and transitory (selective advantage of graded oxygen affinities) adaptation to hypoxia is discussed. A survey on the sequence homology of the globin chains of geese (Anserinae) and ducks (Anatinae) is given.

Partial sequence of hemoglobin from cobra (Naja naja naja)

Hemoglobin from the cobra snake, Naja naja naja, was isolated and its chains separated on a CM-cellulose column. The separation profile revealed an alpha and two beta chains having the molar proportions of [alpha]2[beta 1]1[beta 2]1. The N-terminal amino acid sequence of the intact chains and of the CNBr peptides were carried out. The beta 2 chain was found to be heterogeneous comprising a minor component amounting to 11%. This later showed changes at two positions 9 and 14 in the first 30 residues sequenced.

High sulfhydryl content in turtle erythrocytes: is there a relation with resistance to hypoxia?

Glutathione concentration in the erythrocytes of the fresh-water turtle Phrynops hilarii, as determined by the enzymic recycling method is 1.9 +/- 0.2 mM. The erythrocyte non-protein -SH, NPSH, content, as determined by the 5,5' dithiobis(2-nitrobenzoic acid), DTNB, reducing capacity is 4.6 +/- 0.8 mM. The total DTNB reducing capacity in the erythrocytes, including hemoglobin, is 26 +/- 5 mM. Incubation with oxidized glutathione, greatly increases the electrophoretic mobility of both hemoglobin components present in the erythrocytes of Phrynops hilarii, indicating the formation of mixed disulphides with glutathione. The high --SH content in the erythrocytes of P. hilarii might be part of a redox buffering principally an antioxidant mechanism involved in resistance to hypoxia, possibly along the hypoxic period as well as during reperfusion with oxygen.