Subunit interactions of Glycera dibranchiata hemoglobin

Direct comparison of oligochaete erythrocruorins as potential blood substitutes

While many blood substitutes are based on mammalian hemoglobins (e.g., human hemoglobin, HbA), the naturally extracellular hemoglobins of invertebrates (a.k.a. erythrocruorins, Ecs) are intriguing alternative oxygen carriers. Specifically, the erythrocruorin of Lumbricus terrestris has been shown to effectively deliver oxygen in mice and rats without the negative side effects observed with HbA. In this study, the properties of six oligochaete Ecs (Lumbricus terrestris, Eisenia hortensis, Eisenia fetida, Eisenia veneta, Eudrilus eugeniae, and Amynthas gracilis) were compared in vitro to identify the most promising blood substitute candidate(s). Several metrics were used to compare the Ecs, including their oxidation rates, dissociation at physiological pH, thermal stability, and oxygen transport characteristics. Overall, the Ecs of Lumbricus terrestris (LtEc) and Eisenia fetida (EfEc) were identified as promising candidates, since they demonstrated high thermal and oligomeric stability, while also exhibiting relatively low oxidation rates. Interestingly, the O₂ affinity of LtEc (P₅₀ = 26.25 mmHg at 37 °C) was also observed to be uniquely lower than EfEc and all of the other Ecs (P₅₀ = 9.29–13.62 mmHg). Subsequent alignment of the primary sequences of LtEc and EfEc revealed several significant amino acid substitutions within the D subunit interfaces that may be responsible for this significant change in O₂ affinity. Nonetheless, these results show that LtEc and EfEc are promising potential blood substitutes that are resistant to oxidation and denaturation, but additional experiments will need to be conducted to determine their safety, efficacy, and the effects of their disparate oxygen affinities in vivo.

Purification of diverse hemoglobins by metal salt precipitation

Although donated blood is the preferred material for transfusion, its limited availability and stringent storage requirements have motivated the development of blood substitutes. The giant extracellular hemoglobin (aka erythrocruorin) of the earthworm Lumbricus terrestris (LtEc) has shown promise as a blood substitute, but an efficient purification method for LtEc must be developed to meet the potential large demand for blood substitutes. In this work, an optimized purification process that uses divalent and trivalent metal salts to selectively precipitate human, earthworm, and bloodworm hemoglobin (HbA, LtEc, and GdHb, respectively) from crude solutions was developed. Although several metal ions were able to selectively precipitate LtEc, Zn(2+) and Ni(2+) provided the lowest heme oxidation and highest overall yield of LtEc. In contrast, Zn(2+) was the only metal ion that completely precipitated HbA and GdHb. Polyacrylamide gel electrophoresis (PAGE) analysis shows that metal precipitation removes several impurities to provide highly pure hemoglobin samples. Heme oxidation levels were relatively low for Zn(2+)-purified HbA and LtEc (2.4±1.3% and 5.3±2.1%, respectively), but slightly higher for Ni(2+)-purified LtEc (8.4±1.2%). The oxygen affinity and cooperativity of the precipitated samples are also identical to samples purified with tangential flow filtration (TFF) alone, indicating the metal precipitation does not significantly affect the function of the hemoglobins. Overall, these results show that hemoglobins from several different species can be highly purified using a combination of metal (Zn(2+)) precipitation and tangential flow filtration.

Mitochondrial depolarization following hydrogen sulfide exposure in erythrocytes from a sulfide-tolerant marine invertebrate

Sulfide-tolerant marine invertebrates employ a variety of mechanisms to detoxify sulfide once it has entered their bodies, but their integumentary,respiratory epithelium and circulatory cells may still be exposed to toxic sulfide concentrations. To investigate whether sulfide exposure is toxic to mitochondria of a sulfide-tolerant invertebrate, we used the fluorescent dyes JC-1 and TMRM to determine the effect of sulfide exposure on mitochondrial depolarization in erythrocytes from the annelid Glycera dibranchiata. In erythrocytes exposed to 0.11-1.9 mmol l-1 sulfide for 1 h, the dyes showed fluorescence changes consistent with sulfide-induced mitochondrial depolarization. At the highest sulfide concentration, the extent of depolarization was equivalent to that caused by the mitochondrial uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP). Even when induced by as little as 0.3 mmol l-1 sulfide, the depolarization was not reversible over a subsequent 5 h recovery period. The mechanism of toxicity was likely not via inhibition of cytochrome c oxidase (COX),since other COX inhibitors and other mitochondrial electron transport chain inhibitors did not produce similar effects. Furthermore, pharmacological inhibition of the mitochondrial permeability transition pore failed to prevent sulfide-induced depolarization. Finally, increased oxidation of the free radical indicators H2DCFDA and MitoSOX™ in erythrocytes exposed to sulfide suggests that sulfide oxidation increased oxidative stress and superoxide production, respectively. Together, these results indicate that sulfide exposure causes mitochondrial depolarization in cells of a sulfide-tolerant annelid, and that this effect, which differs from the actions of other COX inhibitors, may be via increased free radical damage.

Crystal structures of unligated and CN-ligated Glycera dibranchiata monomer ferric hemoglobin components III and IV

Erythrocytes of the marine annelid, Glycera dibranchiata, contain a mixture of monomeric and polymeric hemoglobins. There are three major monomer hemoglobin components, II, III, IV (also called GMH2, 3, and 4), that have been highly purified and well characterized. We have now crystallized GMH3 and GMH4 and determined their structures to 1.4-1.8 A resolution. The structures were determined for these two monomer hemoglobins in the oxidized (Fe3+, ferric, or met-) forms in both the unligated and cyanide-ligated states. This work differs from two published, refined structures of a Glycera dibranchiata monomer hemoglobin, which has a sequence that is substantially different from any bona fide major monomer hemoglobins (GMH2, 3, or 4). The high-resolution crystal structures (presented here) and the previous NMR structure of CO-ligated GMH4, provide a basis for interpreting structure/function details of the monomer hemoglobins. These details include: (1) the strong correlation between temperature factor and NMR dynamics for respective protein forms; (2) the unique nature of the HisE7Leu primary sequence substitutions in GMH3 and GMH4 and their impact on cyanide ion binding kinetics; (3) the LeuB10Phe difference between GMH3 and GMH4 and its impact on ligand binding; and (4) elucidation of changes in the structural details of the distal and proximal heme pockets upon cyanide binding.

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.

Complete amino acid sequence of the Glycera dibranchiata monomer hemoglobin component IV: structural implications

The globin derived from the monomer Component IV hemoglobin of the marine amnelid, Glycera dibranchiata, has been completely sequenced, and the resulting information has been used to create a structural model of the protein. The most important result is that the consensus sequence of Component IV differs by 3 amino acids from a cDNA-predicted amino acid sequence thought earlier to encode the Component IV hemoglobin. This work reveals that the histidine (E7), typical of most heme-containing globins, is replaced by leucine in Component IV. Also significant is that this sequence is not identical to any of the previously reported Glycera dibranchiata monomer hemoglobin sequences, including the sequence from a previously reported crystal structure, but has high identity to all. A three-dimensional structural model for monomer Component IV hemoglobin was constructed using the published 1.5 A crystal structure of a monomer hemoglobin from Glycera dibranchiata as a template. The model shows several interesting features: (1) a Phe31 (B10) that is positioned in the active site; (2) a His39 occurs in an interhelical region occupied by Pro in 98.2% of reported globin sequences; and (3) a Met41 is found at a position that emerges from this work as a previously unrecognized heme contact.

Adventitious variability? The amino acid sequences of nonvertebrate globins

1. The more than 140 amino acid sequences of non-vertebrate hemoglobins (Hbs) and myoglobins (Mbs) that are known at present, can be divided into several distinct groups: (1) single-chain globins, containing one heme-binding domain; (2) truncated, single-chain, one-domain globins; (3) chimeric, one-domain globins; (4) chimeric, two-domain globins; and (5) chimeric multi-domain globins. 2. The crystal structures of eight nonvertebrate Hbs and Mbs are known, all of them monomeric, one-domain globin chains. Although these molecules represent plants, prokaryotes and several metazoan groups, and although the inter-subunit interactions in the dimeric and tetrameric molecules differ from the ones observed in vertebrate Hbs, the secondary structures of all seven one-domain globins retain the characteristic vertebrate "myoglobin fold". No crystal structures of globins representing the other four groups have been determined. 3. Furthermore, a number of the one-, two- and multi-domain globin chains participate in a broad variety of quaternary structures, ranging from homo- and heterodimers to highly complex, multisubunit aggregates with M(r) > 3000 kDa (S. N. Vinogradov, Comp. Biochem. Physiol. 82B, 1-15, 1985). 4. (1) The single-chain, single-domain globins are comparable in size to the vertebrate globins and exhibit the widest distribution. (A) Intracellular Hbs include: (i) the monomeric and polymeric Hbs of the polychaete Glycera; (ii) the tetrameric Hb of the echiuran Urechis; (iii) the dimeric Hbs of echinoderms such as Paracaudina and Caudina; and (iv) the dimeric and tetrameric Hbs of molluscs, the bivalves Scapharca, Anadara, Barbatia and Calyptogena. (B) Extracellular Hbs include: (i) the multiple monomeric and dimeric Hbs of the larva of the insect Chironomus; (ii) the Hbs of nematodes such as Trichostrongylus and Caenorhabditis; (iii) the globin chains forming tetramers and dodecamers and comprising approximately 2/3 of the giant (approximately 3600 kDa), hexagonal bilayer (HBL) Hbs of annelids, e.g. the oligochaete Lumbricus and the polychaete Tylorrhynchus and of the vestimentiferan Lamellibrachia; and (iv) the globin chains comprising the ca 400 kDa Hbs of Lamellibrachia and the pogonophoran Oligobrachia. (C) Cytoplasmic Hbs include: (i) the Mbs of molluscs, the gastropods Aplysia, Bursatella, Cerithedea, Nassa and Dolabella and the chiton Liolophura; (ii) the three Hb of the symbiont-harboring bivalve Lucina; (iii) the dimeric Hb of the bacterium Vitreoscilla; and (iv) plant Hbs, including the Hbs of symbiont-containing legumes (Lgbs), the Hbs of symbiont-containing non-leguminous plants and the Hbs in the roots of symbiont-free plants.(ABSTRACT TRUNCATED AT 400 WORDS)

The heterogeneity of the polymeric intracellular hemoglobin of Glycera dibranchiata and the cDNA-derived amino acid sequence of one component

The erythrocytes of the marine polychaete Glycera dibranchiata contain a number of different, single-chain hemoglobins, some of which self-associate into a 'polymeric' fraction. An oligodeoxynucleotide probe was synthesized based on partial amino acid sequences determined by chemical methods, and used to screen a cDNA library constructed from the poly(A+)mRNA of Glycera erythrocytes (Simons, P.C. and Satterlee, J.D. (1989) Biochemistry 28, 8525-8530). The longest positive inserts found were sequenced using the dideoxy nucleotide chain termination method. One complete clone was obtained: clone 5A, 816 bases long, contained 59 bases of 5'-untranslated RNA, an open reading frame of 441 bases coding for 147 amino acids and a 3'-untranslated region of 316 bases. The derived amino acid sequence of Glycera globin P1 was in agreement with the partial amino acid sequences obtained by chemical methods. Three additional inserts obtained in the screening were also sequenced: the inferred amino acid sequences proved to be partial globin sequences which were different from each other and from the sequence of P1. Thus, the 'polymeric' fraction of the intracellular hemoglobin of Glycera probably consists of at least four different globin chains much like the 'monomeric' fraction. Comparison of the 'polymeric' sequence with the two known 'monomeric' sequences, M-II and M-IV, shows that they share 54 identical residues. At 74 positions, the identical residues in M-II and M-IV differ from the corresponding residue in P1, including at E-7, where P1 has a distal His, in contrast to Leu in M-II and M-IV. The alignment of Bashford et al. ((1987) J. Mol. Biol. 196, 199-216) and their templates were used to examine the principal differences between the two types of Glycera globin sequences. They appear to consist of uncommon surface amino acid residues at positions C6 (Phe vs. Ala), E10 (Val vs. Lys), E17 (Lys vs. Val), G1 (Arg vs. Lys), G10 (Met vs. Ala) and H5 (Arg vs. Lys). One or more of these residues could be responsible for the self-association exhibited by the 'polymeric' Glycera globins.

Glycera dibranchiata hemoglobin. Structure and refinement at 1.5 A resolution

The coelomic cells of the common marine bloodworm Glycera dibranchiata contain several hemoglobin monomers and polydisperse polymers. We present the refined structure of one of the Glycera monomers at 1.5 A resolution. The molecular model for protein and ordered solvent for the deoxy form of the Glycera monomer has been refined to a crystallographic R-factor of 12.7% against an X-ray diffraction dataset at 1.5 A resolution. The positions of 1095 protein atoms have been determined with a maximum root-mean-square (r.m.s.) error of 0.13 A, and the r.m.s. deviation from ideal bond lengths is 0.015 A and from ideal bond angles is 1.0 degree. The r.m.s. deviation of planar groups from their least-squares planes is 0.007 A, and the r.m.s. deviation for torsion angles is 1.2 degrees for peptide groups and 16.8 degrees for side-chains. A total of 153 water molecules has been located, and they have been refined to a final average occupancy of 0.80. Multiple conformations have been found for five side-chains, and a change has been suggested for the sequence at five residues. The heme group is present in the "reverse" orientation that differs only in the positions of the vinyl beta-carbons from the "normal" orientation. The doming of the heme towards the proximal side, and the bond distances and angles of the heme and proximal histidine are typical of most deoxy globin structures. The substitution of leucine for the distal histidine residue (E7) creates an unusually hydrophobic heme pocket.

Anadara ovalis hemoglobins: distinct dissociation and ligand binding characteristics

The red cells of the arcid clam Anadara ovalis contain two electrophoretically distinct hemoglobins: Hb Major (Hb Ma) and Hb Minor (Hb Mi). The major component consists of two electrophoretically indistinguishable tetramers each composed of two heterodimers; the minor hemoblogin is a homodimer whose subunits are different from the tetramer. Functionally, Hb Ma has a higher P50, exhibits a concentration dependent oxygen affinity, has significant ligand cooperativity (n = 2.0), lacks a Bohr effect and is unaffected by ATP. HB Mi has a P50 which is lower and independent of hemoglobin concentration, shows appreciable cooperativity (n = 1.4) and exhibits no heterotropic effects. Both Hb Ma and Mi are resistant to dissociation in the presence of 1.0 M NaI, NaCl and guanidine-HCl but dissociate to monomers when converted to the aquamet but not the cyanmet derivative. The dissociation is completely inhibited by mercaptoethanol. The large number of reactive -SH groups (10-13 per tetramer) suggests that the monomerization is mediated by intra-subunit disulfide bridge formation.

Solution studies on heme proteins. Circular dichroism and optical rotation of Glycera dibranchiata hemoglobins

Circular dichroism (CD) and optical rotatory dispersion (ORD) spectra of several liganded derivatives of the monomer and polymer hemoglobin components of the marine annelid, Glycera dibranchiata were measured over the wavelength range 650--195 nm. The differences observed between the monomer and polymer components for the heme dichroic bands in the visible, Soret and ultraviolet wavelength regions seem to result from changes in the heme environment, geometry and coordination state of the central heme iron in these proteins. Within the Soret region, the liganded derivatives of the monomer hemoglobin exhibit predominantly negative circular dichroic bands. The heme band at 260 nm is also absent for the monomer hemoglobin. The ORD and CD spectra in the far-ultraviolet, peptide absorbing region suggest also differences in the alpha-helix content of the monomer and polymer hemoglobins. The values for the single-chain G. dibranchiata hemoglobin are in the expected range (about 70% alpha-helix) as predicted by the X-ray structure of this protein. The lower estimates of the alpha-helix content for the polymer hemoglobin (approx. 50%), may reflect the differences in amino acid composition, primary structure and polypeptide chain foldings. Changes in oxidation state and ligand binding appears to have no pronounced effect on the helicity of either the monomer or polymer hemoglobins. The removal of the heme moiety from the monomer hemoglobin did result in a major decrease in its helix content similar to the loss of heme from myoglobin.