Complete amino acid sequence of the myoglobin from the Pacific spotted dolphin, Stenella attenuata graffmani

Isolation of heat-tolerant myoglobin from Asian swamp eel Monopterus albus

Myoglobin from Asian swamp eel Monopterus albus was purified from fish muscle using salt fractionation followed by column chromatography and molecular filtration. The purified Mb of 0.68 mg/g wet weight of muscle was determined for its molecular mass by MALDI-TOF-MS to be 15,525.18 Da. Using isoelectric focusing technique, the purified Mb showed two derivatives with pI of 6.40 and 7.12. Six peptide fragments of this protein identified by LC-MS/MS were homologous to Mbs of sea raven Hemitripterus americanus, yellowfin tuna Thunnus albacores, blue marlin Makaira nigicans, common carp Cyprinus carpio, and goldfish Carassius auratus. According to the Mb denaturation, the swamp eel Mb had thermal stability higher than walking catfish Clarias batrachus Mb and striped catfish Pangasius hypophthalmus Mb, between 30 and 60 (°)C. For the thermal stability of Mb, the swamp eel Mb showed a biphasic behavior due to the O(2) dissociation and the heme orientation disorder, with the lowest increase in both Kd(f) and Kd(s). The thermal sensitivity of swamp eel Mb was lower than those of the other Mbs for both of fast and slow reaction stages. These results suggest that the swamp eel Mb globin structure is thermally stable, which is consistent with heat-tolerant behavior of the swamp eel particularly in drought habitat.

cDNA-derived amino acid sequences of myoglobins from nine species of whales and dolphins

We determined the myoglobin (Mb) cDNA sequences of nine cetaceans, of which six are the first reports of Mb sequences: sei whale (Balaenoptera borealis), Bryde's whale (Balaenoptera edeni), pygmy sperm whale (Kogia breviceps), Stejneger's beaked whale (Mesoplodon stejnegeri), Longman's beaked whale (Indopacetus pacificus), and melon-headed whale (Peponocephala electra), and three confirm the previously determined chemical amino acid sequences: sperm whale (Physeter macrocephalus), common minke whale (Balaenoptera acutorostrata) and pantropical spotted dolphin (Stenella attenuata). We found two types of Mb in the skeletal muscle of pantropical spotted dolphin: Mb I with the same amino acid sequence as that deposited in the protein database, and Mb II, which differs at two amino acid residues compared with Mb I. Using an alignment of the amino acid or cDNA sequences of cetacean Mb, we constructed a phylogenetic tree by the NJ method. Clustering of cetacean Mb amino acid and cDNA sequences essentially follows the classical taxonomy of cetaceans, suggesting that Mb sequence data is valid for classification of cetaceans at least to the family level.

Molecular charge and electrophoretic mobility in cetacean myoglobins of known sequence

Fourteen myoglobins of known sequence were examined by polyacrylamide gel electrophoresis at five pH values. Gels at each pH divided the sequences into six to eight distinct classes, while the combination of the results of three gels at different pH levels distinguished 13 of 14, or 93%, of the sequences. The relative mobility of the myoglobins in the gels is significantly correlated with the charges of the proteins calculated from the pK values of the ionized groups. Major differences in mobility corresponded to expected differences in charge due to the amino acid substitutions between sequences. In addition to sequences differing in the total number of acidic and basic residues, those differing from each other in the total number of histidines were distinguished on low-pH gels. One pair of sequences differing by the exchange of lysine for arginine was separated on high-pH gels, as predicted from the differences in ionization of these two amino acids. On gels at pH 10.4, there was greater deviation of electrophoretic mobility from charge than on other gels, possibly due to the influence of amino acid substitutions in the neighborhood of lysine residues. Manipulation of the concentration and composition of the gels did not change the separation of the sequences from each other. Examination of myoglobins by gel electrophoresis at a wide range of pH values allows discrimination of nearly all amino acid substitutions and demonstrates the close relationship between titration and relative electrophoretic mobility.

Reassignment of residue 122 in the myoglobin from the killer whale, Orcinus orca

The complete amino acid sequence of the major component myoglobin from killer whale, Orcinus orca, was determined by automated Edman degradation. In this study residue 122 was found to be glutamic acid instead of glutamine as was originally reported (Castillo et al. 1977). This reassignment affects the phylogenetic relationship of killer whale myoglobin with the myoglobins from other closely related cetacean species and also affects studies concerned with the physical parameters of the protein.

Complete amino acid sequence of the major component myoglobin from the goose-beaked whale, Ziphius cavirostris

The complete primary structure of the major component myoglobin from the goose-beaked whale, Ziphius cavirostris, was determined by specific cleavage of the protein to obtain large peptides which are readily degraded by the automatic sequencer. Over 80% of the amino acid sequence was established from the three peptides resulting from the cleavage of the apomyoglobin at its two methionine residues with cyanogen bromide along with the four peptides resulting from the cleavage with trypsin of the citraconylated apomyoglobin at its three arginine residues. Further digestion of the central cyanogen bromide peptide with S. aureus strain V8 protease and the 1,2-cyclohexanedione-treated central cyanogen bromide peptide with trypsin enabled the determination of the remainder of the covalent structure. This myoglobin differs from the cetacean myoglobins determined to date at 12 to 17 positions. These large sequence differences reflect the distant taxonomic relationships between the goose-beaked whale and the other species of Cetacea the myoglobin sequences of which have previously been determined.

Complete amino acid sequence of the major component myoglobin from Hubb's beaked whale, Mesoplodon carlhubbsi

The complete primary structure of the major component myoglobin from Hubb's beaked whale, Mesoplodon carlhubbsi, was determined by specific cleavage of the protein to obtain large peptides which are readily degraded by the automatic sequencer. In all experiments a Beckman 890C automatic sequencer was used to degrade the peptides. A cyanogen bromide digest was used to fragment the protein at its two methionine residues into three fragments which were separated by gel filtration. In a similar pattern the protein was citraconylated to protect the lysine residues and the modified protein fragmented at its arginine residues with trypsin. The three peptides obtained here were also purified by gel filtration. Sequencer analysis of the whole apoprotein, cyanogen bromide fragments and the peptides cleaved at the arginine residues with trypsin provided 80% of the completed sequence. The remainder of the sequence was obtained by digesting the middle cyanogen bromide fragment with staphylococcal protease and by total tryptic digestion of the whole apoprotein and isolating the resulting peptides by ion-exchange chromatography. The primary structure of the Mesoplodon carlhubbsi myoglobin represents a sequence which may be closey related to the ancestral sequence of all cetacean myoglobins.

Evolution of the amino acid substitution in the mammalian myoglobin gene

Multivariate statistical analyses were applied to 16 physical and chemical properties of amino acids. Four of these properties; volume, polarity, isoelectric point (charge), and hydrophobicity were found to explain adequately 96% of the total variance of amino acid attributes. Using these four quantitative measures of amino acid properties, a structural discriminate function in the form of a weighted difference sum of squares equation was developed. The discriminate function is weighted by the location of each particular residue within a given tertiary structure and yields a numerical discriminate or difference value for the replacement of these residues by different amino acids. This resulting discriminate value represents an expression of the perturbation in the local positional environment of a protein when an amino acid substitution occurs. With the use of this structural discriminate function, a residue by residue comparison of the known mammalian myoglobin sequences was carried out in an attempt to elucidate the positions of possible deviations from the known tertiary structure of sperm whale myoglobin. Only 11 of the 153 residue positions in myoglobin demonstrated possible structural deviations. From this analysis, indices of difference were calculated for all amino acid exchanges between the various myoglobins. All comparisons yielded indices of difference that were considerably lower than would be expected if mutations had been fixed at random, even if the organization of the genetic code is taken into consideration. On the basis of these results, it is inferred that some form of selection has acted in the evolution of mammalian myoglobins to favor amino acid substitutions that are compatible with the retention of the original conformation of the protein.

Complete amino acid sequence of the myoglobin from the Pacific sei whale, Balaenoptera borealis

The complete amino acid sequence of the major component myoglobin from Pacific sei whale, Balaenoptera borealis, was determined by specific cleavage of the protein to obtain large peptides which are readily degraded by the automatic sequencer. The acetimidated apomyoglobin was selectively cleaved at its two methionyl residues with cyanogen bromide and at its three arginyl residues by trypsin. From the sequence analysis of four of these peptides and the apomyoglobin, over 75% of the covalent structure of the protein was obtained. The remainder of the primary structure was determined by the sequence analysis of peptides that resulted from further digestion of the amino-terminal and central cyanogen bromide fragments. The amino-terminal fragment was specifically cleaved at its two tryptophanyl residues with N-chlorosuccinimide and the central cyanogen bromide fragment was cleaved at its glutamyl residues with staphylococcal protease and at its single tyrosyl residue with N-bromosuccinimide. The primary structure of this myoglobin proved identical with that from the gray whale but differs from that of the finback whale at four positions, from that of the minke whale at three positions and from the myoglobin of the humpback whale at one position. The above sequence identities and differences reflect the close taxonomic relationship of these five species of Cetacea.