Primary structure of hemoglobin from cobra Naja naja naja

The Primary Structure of β(I)-Chain of Hemoglobin from Snake Sindhi Krait (Bungarus sindanus sindanus)

The amino acid sequence of β(I)-globin chain from Sindhi Krait (Bungarus sindanus sindanus) was determined to study the molecular evolution among snakes. The hemoglobin was isolated from the red blood cells and was analyzed by ion-exchange chromatography (IEX). The crude globin was subjected to reversed phased-high performance liquid chromatography (RP-HPLC) using C4 column. The N-terminal sequences of intact globin chains and tryptic peptides were determined by Edman degradation in a pulsed liquid gas phase sequencer using an online Phenylthiohydantoin analyzer. Sindhi Krait is expected to express three hemoglobin components that are composed of β(II), β(I), α(D) and α(A)-globin chains, as apparent by IEX, RP-HPLC and N-terminal sequence analyses. Sequence alignment and phylogenetic analyses of β(I) globin chain from Sindhi Krait showed closest relationship with β(I) globin chain from Rattlesnake, Water snake and Indigo snake. Interestingly, comparison of primary sequence of β(I) globin chain of Sindhi Krait with human β chain revealed 63 % similarity along with the retention of all heme contact points. Variations among the two sequences were prominent at αβ contact points and in regions directly not important for function.

The conserved Phe GH5 of importance for hemoglobin intersubunit contact is mutated in gadoid fish

Background

Functionality of the tetrameric hemoglobin molecule seems to be determined by a few amino acids located in key positions. Oxygen binding encompasses structural changes at the interfaces between the α1β2 and α2β1 dimers, but also subunit interactions are important for the oxygen binding affinity and stability. The latter packing contacts include the conserved Arg B12 interacting with Phe GH5, which is replaced by Leu and Tyr in the α^A and α^D chains, respectively, of birds and reptiles.

Results

Searching all known hemoglobins from a variety of gnathostome species (jawed vertebrates) revealed the almost invariant Arg B12 coded by the AGG triplet positioned at an exon-intron boundary. Rare substitutions of Arg B12 in the gnathostome β globins were found in pig, tree shrew and scaled reptiles. Phe GH5 is also highly conserved in the β globins, except for the Leu replacement in the β1 globin of five marine gadoid species, gilthead seabream and the Comoran coelacanth, while Cys and Ile were found in burbot and yellow croaker, respectively. Atlantic cod β1 globin showed a Leu/Met polymorphism at position GH5 dominated by the Met variant in northwest-Atlantic populations that was rarely found in northeast-Atlantic cod. Site-specific analyses identified six consensus codons under positive selection, including 122β(GH5), indicating that the amino acid changes identified at this position may offer an adaptive advantage. In fact, computational mutation analysis showed that the replacement of Phe GH5 with Leu or Cys decreased the number of van der Waals contacts essentially in the deoxy form that probably causes a slight increase in the oxygen binding affinity.

Conclusions

The almost invariant Arg B12 and the AGG codon seem to be important for the packing contacts and pre-mRNA processing, respectively, but the rare mutations identified might be beneficial. The Leu122β1(GH5)Met and Met55β1(D6)Val polymorphisms in Atlantic cod hemoglobin modify the intradimer contacts B12-GH5 and H2-D6, while amino acid replacements at these positions in avian hemoglobin seem to be evolutionary adaptive in air-breathing vertebrates. The results support the theory that adaptive changes in hemoglobin functions are caused by a few substitutions at key positions.

Chromatin supraorganization, DNA fragmentation, and cell death in snake erythrocytes

In nucleate erythrocytes of several vertebrate groups, the frequency and intensity of DNA fragmentation associated with programed cell death vary considerably. Although hemoglobin efficiency may be related to erythrocyte life span, and hemoglobin types and erythrocyte life spans are assumed to vary in reptiles, no data on DNA fragmentation and chromatin organization as related to cell death exist for snakes. In the present study, chromatin supraorganization, DNA fragmentation, and cell death were investigated in four snake species (Crotalus durissus terrificus, Bothrops jararaca, Bothrops alternatus, and Bothrops neuwiedii), which differ in their geographical distribution and habitats, by using image analysis of Feulgen hydrolysis kinetics, the TUNEL assay, single-cell gel electrophoresis, and transmission electron microscopy. Relatively few circulating erythrocytes were found to be simultaneously committed to cell death, although there was some variation among the snake species. Conspicuous nuclear and cytoplasmic organelles suggestive of metabolic activity were seen ultrastructurally in most snake erythrocytes. The DNA of the snake erythrocyte chromatin was much more resistant to Feulgen acid hydrolysis (DNA depurination and breakdown) than that of young adult bullfrog erythrocytes, which had a high frequency and intensity of DNA fragmentation. Of the species studied, B. neuwiedii and C. d. terrificus showed the greatest resistance to Feulgen acid hydrolysis and to the DNA fragmentation, revealed by the TUNEL assay. Although B. neuwiedii also showed the lowest frequency of cells with more damaged DNA in the single-cell gel electrophoresis assay, C. d. terrificus had the highest frequency of damaged cells, possibly because of the abundance of alkaline-sensitive DNA sites. The results for DNA fragmentation and cell death in erythrocytes of B. jararaca and B. alternatus generally differed from those for C. d. terrificus and B. neuwiedii and may reflect differences in the biology of these species selected under different geographical habitats. The differences in erythrocyte cell biology reported here may be related to hemoglobin variants selected in the mentioned snake species and that would lead the cells to different resistances to unfavorable environmental conditions.Key words: erythrocytes, snakes, DNA fragmentation, chromatin supraorganization, cell death.

Amino acid sequence of the alpha- and beta-globin chains of the Erabu sea snake (Laticaudia semifasciata)

We determined the complete amino acid sequences of the Erabu sea snake (Laticaudia semifasciata) hemoglobin by analyzing the intact globin chains, enzymatically digested fragments, and chemical cleavage fragments to clarify the molecular evolution and phylogenetic classification of the sea snake. The Erabu sea snake has two types of hemoglobin components, Hb-I and Hb-II, which contain different alpha- and beta-chains. This is the second report of the complete primary structure for hemoglobin of snakes. The sequences were compared with those of other reptilian hemoglobins. Amino acids at positions critical for the structure and physiological functions of hemoglobin were loosely conserved. The requirements for binding of ATP and of diphosphoglycerate as allosteric effectors of beta-globins seemed to be fulfilled.

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.

Embryonic globins of the marsupial the Tammar Wallaby (Macropus eugenii): bird like and mammal like

1. Tammar Wallaby embryonic blood has been shown to have three alpha-like and two beta-like globin chains in its four haemoglobin components and partial sequences of several chains have been determined. 2. The major embryonic beta-like chain (epsilon) is similar to other mammalian embryonic beta-like chains on the basis of sequencing its first 60 amino acids. 3. There is another embryonic beta-like chain present in one haemoglobin component. It was designated omega and, in its first 54 amino acids, it has features that are more like avian globins than mammalian globins. 4. The one alpha-like embryonic globin sequenced has mammalian rather than avian characteristics. 5. A provisional phylogenetic tree of beta-like globins has been determined. The Tammar epsilon-globin forms a monophyletic group with marsupial and other mammalian embryonic globins; the omega-globin forms a monophyletic group with bird adult and embryonic globins.