The amino acid sequences of two alpha chains of hemoglobins from Komodo dragon Varanus komodoensis and phylogenetic relationships of amniotes

Abstract

To elucidate phylogenetic relationships among amniotes and the evolution of alpha globins, hemoglobins were analyzed from the Komodo dragon (Komodo monitor lizard) Varanus komodoensis, the world's largest extant lizard, inhabiting Komodo Islands, Indonesia. Four unique globin chains (alpha A, alpha D, beta B, and beta C) were isolated in an equal molar ratio by high performance liquid chromatography from the hemolysate. The amino acid sequences of two alpha chains were determined. The alpha D chain has a glutamine at E7 as does an alpha chain of a snake, Liophis miliaris, but the alpha A chain has a histidine at E7 like the majority of hemoglobins. Phylogenetic analyses of 19 globins including two alpha chains of Komodo dragon and ones from representative amniotes showed the following results: (1) The a chains of squamates (snakes and lizards), which have a glutamine at E7, are clustered with the embryonic alpha globin family, which typically includes the alpha D chain from birds; (2) birds form a sister group with other reptiles but not with mammals; (3) the genes for embryonic and adult types of alpha globins were possibly produced by duplication of the ancestral alpha gene before ancestral amniotes diverged, indicating that each of the present amniotes might carry descendants of the two types of alpha globin genes; (4) squamates first split off from the ancestor of other reptiles and birds.

The Amino Acid Sequences of the α- and β-Globin Chains of Hemoglobin from the Aldabra Giant Tortoises, Geochelone gigantea

“…In comparison with the structural data of β-globin of Hb A (Shishikura and Takami, 2001), the primary structure of β-globin derived from the Hb D was completely identical, indicating that the β-globin was common in the construction of the two adult hemoglobin components, Hb A and Hb D. This finding supports the studies of Rücknagel and Braunitzer (1988) who described that the red blood cells shared the same β-globin chains in Hb A and Hb D. The sharing of identical β-globin chains has also been demonstrated in crocodiles (Leclercq et al, 1981;Leclercq et al, 1982), while lizards and snakes express two adult β-types of globins (Rücknagel et al, 1988;Matsuura et al, 1989;Abbasi and Braunitzer, 1991;Naqvi et al, 1994;Fushitani et al, 1996;Gorr et al, 1998). In this context, adult mammals (Braunitzer et al, 1961;Leclercq et al, 1981) and birds (Rücknagel et al, 1984;Oberthür et al, 1983;Oberthür et al, 1986) have been reported to have one kind of β-globin, but adult frogs (Knöchel et al, 1983;Patient et al, 1983) contained two subtypes of β-globin chains.…”

“…shows a molecular tree of reptilian evolution constructed mainly by α D -globins of 7 reptiles as well as relatedness among representatives of adult and embryonic α -type globins. The tree also strongly supports the previous molecular studies (Goodman et al ., 1975;Fushitani et al ., 1996;Gorr et al ., 1998;Shishikura and Takami, 2001), however, it is reasonable to note the following two points: (1) the two kinds of embryonic globins, π ' and ζ , first split off from the ancestor of the α -type of globins and formed a cluster; (2) the ancestor of squamates (snakes; L. miliaris , lizards; Varanus komodoensis ) occupied unusual positions since α Dglobins of squamates began to diverge approximately 335 million years ago, much earlier than the separation of the three other clusters of α -type globin families.…”

“…Amniota (reptiles, birds and mammals), in general, have two or more hemoglobin components (Brown and Ingram, 1974;Moss and Hamilton, 1974;Lawn et al ., 1978;Efstratiadis et al ., 1980;Bunn and Forget, 1986;Fushitani et al ., 1996;Gorr et al , 1998) that are expressed according to the demands of different physiological conditions. Among them, hemoglobin D (Hb D) was first found in birds as a minor component of the embryonic and adult definitive erythrocytes (Hagopian and Ingram, 1971;Brown and Ingram, 1974).…”

“…Based on functional studies of Hb D, the presence of α D -globin raises the oxygen affinity and might be one such adaptation of insufficient oxygen supply as observed in the embryonic stages (Dodgson et al ., 1981;Chapman et al ., 1982) or extreme hypoxic and even anoxic conditions (Rücknagel and Braunitzer, 1988). On the other hand, the primary structure of α D -globin of Hb D shows closely resemblance with embryonic hemoglobins (Chapman et al ., 1982) and thus, the Hb D is of interest for the study of the molecular evolution of Amniota globins because the distribution of the α D -globin, to date, has been restricted in Aves and Reptilia (Rücknagel et al ., 1984;Abbasi et al ., 1988;Rücknagel et al ., 1988;Matsuura et al ., 1989;Fushitani et al ., 1996;Gorr et al ., 1998;Accession No. AF304335 in GenBank;Shishikura and Takami, 2001), except for Crocodilia (Leclercq et al ., 1981;Leclercq et al ., 1982).…”

The evolutionary position of turtles revised

“…Several other studies clustered turtles with archosaurs rather than with lepidosaurs (Fitch and Margoliash 1967;Fushitani et al 1996;Mannen et al 1997;Gorr et al 1998;Grishin 1999). However, these studies were based on rather small nuclear sequence data sets, some were based on gene families with complex paralogy relationships (Fushitani et al 1996;Mannen et al 1997;Gorr et al 1998), and some did not include representatives of all the main lineages of amniotes (Fitch and Margoliash 1967;Grishin 1999).…”