Leech extracellular hemoglobin: two globin strains that are akin to vertebrate hemoglobin alpha and beta chains

Recent Insights into the Diversity and Evolution of Invertebrate Hemerythrins and Extracellular Globins

There are three broad groups of oxygen-transport proteins found in the haemolymph (blood) of invertebrates, namely the hemocyanins, the hemerythrins and the globins. Both hemerythrins and extracellular globins are iron-based proteins that are understudied when compared to the copper-containing hemocyanins. Recent evidence suggests that hemerythrins and (giant) extracellular globins (and their linker chains) are more widely distributed than previously thought and may have biological functions beyond oxygen transport and storage. Herein, we review contemporary literature of these often-neglected proteins with respect to their structural configurations on formation and ancestral states.

The complete amino acid sequences of four globins from the land leech Haemadipsa zeylanica var. japonica

The amino acid sequences of four globins from the land leech, Haemadipsa zeylanica var. japonica, were determined using nucleotide sequencing and protein sequencing. The mature globin-molecules were composed of 146 amino acid residues for M-1 globin, 156 for M-2 globin, 143 for D-1 globin, and 149 for D-2 globin. Alignment of the four kinds of globins by Clustal X revealed 22 invariant amino acids. The four globins were 26-33% identical. A striking feature of amino acid alteration was: the replacement of the E7 distal-His of D-1 globin by phenylalanine because histidine is conserved among the rest of the globins of H. zeylanica, those of other representative species (Lumbricus and Tylorrhynchus) of Annelida and most other hemoglobins. A phylogenetic tree constructed of 18 globin structures including two species of leeches, H. zeylanica (a land leech) and Macrobdella decora (a freshwater leech), T. heterochaetus (a representative species of polychaetes), L. terrestris (a representative species of oligochaetes), and human alpha and beta globins strongly indicated that the leech globins first separated from globin lineage of annelids.

Globin and linker sequences of the giant extracellular hemoglobin from the leech Macrobdella decora

A detailed electrospray ionization mass spectrometric study of the approximately 3.5-MDa hexagonal bilayer hemoglobin (HBL Hb) from the pond leech Macrobdella decora has shown it to consist of at least six approximately 17-kDa globin chains, of which two are monomeric and the remaining four occur as disulfide-bonded heterodimers, and three approximately 24-kDa nonglobin linker chains (Weber et al., J. Mol. Biol. 251: 703-720, 1995). The cDNA sequences of the five major constituent chains, globin chains IIA, IIB, B, and C and linker chain L1, are reported here. The globins and linkers share 30%-50% and 20%-30% identity, respectively, with other annelid sequences. Furthermore, IIB and C align with strain A of annelid sequences, whereas IIA and B align with the strain B sequences. Although chains B and C are monomeric, chains IIA and IIB form the main disulfide-bonded dimer. They also have some unusual features: the distal His (E7) is replaced by Phe in IIA, and the highly conserved CD1Phe is replaced by Leu in IIB. In spite of these unusual features, the functional properties of Macrobdella Hb are comparable to those of other HBL Hbs. A phylogenetic analysis of the globin sequences from Macrobdella, the polychaete Tylorrhynchus, the oligochaete Lumbricus, and the vestimentiferan Lamellibrachia, indicates that the two strains originated by gene duplication followed by additional duplication of each of the two strains. The mutation rate of the linkers appeared to be faster than that of the globin chains. The phylogenetic trees constructed using the Maximum Likelihood, Neighbor-Joining and Fitch methods showed the Macrobdella globin sequences to be closest to Lumbricus, in agreement with a view of annelid evolution in which the divergence of the polychaetes occurred before the divergence of the leeches from oligochaetes.

The evolution of extracellular hemoglobins of annelids, vestimentiferans, and pogonophorans

The evolution of extracellular hemoglobins of annelids, vestimentiferans, and pogonophorans was investigated by applying cladistic and distance-based approaches to reconstruct the phylogenetic relationships of this group of respiratory pigments. We performed this study using the aligned sequences of globin and linker chains that are the constituents of these complex molecules. Three novel globin and two novel linker chains of Sabella spallanzanii described in an accompanying paper (Pallavicini, A., Negrisolo, E., Barbato, R., Dewilde, S., Ghiretti-Magaldi, A., Moens, L., and Lanfranchi, G. (2001) J. Biol. Chem. 276, 26384--26390) were also included. Our results allowed us to test previous hypotheses on the evolutionary pathways of these proteins and to formulate a new most parsimonious model of molecular evolution. According to this novel model, the genes coding for the polypeptides forming these composite molecules were already present in the common ancestor of annelids, vestimentiferans, and pogonophorans.

Nonvertebrate hemoglobins: functions and molecular adaptations

Hemoglobin (Hb) occurs in all the kingdoms of living organisms. Its distribution is episodic among the nonvertebrate groups in contrast to vertebrates. Nonvertebrate Hbs range from single-chain globins found in bacteria, algae, protozoa, and plants to large, multisubunit, multidomain Hbs found in nematodes, molluscs and crustaceans, and the giant annelid and vestimentiferan Hbs comprised of globin and nonglobin subunits. Chimeric hemoglobins have been found recently in bacteria and fungi. Hb occurs intracellularly in specific tissues and in circulating red blood cells (RBCs) and freely dissolved in various body fluids. In addition to transporting and storing O(2) and facilitating its diffusion, several novel Hb functions have emerged, including control of nitric oxide (NO) levels in microorganisms, use of NO to control the level of O(2) in nematodes, binding and transport of sulfide in endosymbiont-harboring species and protection against sulfide, scavenging of O(2 )in symbiotic leguminous plants, O(2 )sensing in bacteria and archaebacteria, and dehaloperoxidase activity useful in detoxification of chlorinated materials. This review focuses on the extensive variation in the functional properties of nonvertebrate Hbs, their O(2 )binding affinities, their homotropic interactions (cooperativity), and the sensitivities of these parameters to temperature and heterotropic effectors such as protons and cations. Whenever possible, it attempts to relate the ligand binding properties to the known molecular structures. The divergent and convergent evolutionary trends evident in the structures and functions of nonvertebrate Hbs appear to be adaptive in extending the inhabitable environment available to Hb-containing organisms.