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Primary structure of a dimeric haemoglobin from the deep-sea cold-seep clam Calyptogena soyoae.

ABSTRACT: The heterodont clam Calyptogena soyoae, living in the cold-seep area of the upper bathyal depth of Sagami Bay, Japan, has two homodimeric haemoglobins (Hb I and Hb II) in erythrocytes. The complete amino acid sequence of 136 residues of C. soyoae Hb II was determined. The sequence showed low homology with any other globins (at most 20% identity) and lacked the N-terminal extension of seven to nine amino acid residues characteristic of all the molluscan haemoglobins sequenced hitherto. Although the subunit assembly of molluscan haemoglobin is known to be 'back-to-front' relative to vertebrate haemoglobin, C. soyoae Hb II is unlikely to undergo such a subunit assembly because it lacks homology in the sequence involving subunit interaction. These structural features suggest that C. soyoae haemoglobin may have accomplished a unique molecular evolution. The distal (E7) histidine residue of C. soyoae Hb II is unusually replaced by glutamine. However, the oxyhaemoglobin is stable enough to act as an O2 carrier, since the autoxidation rate at near physiological temperature (3 degrees C) is about 3 times lower than that of human haemoglobin at 37 degrees C. H.p.l.c. patterns of peptides (Figs. 5-7), amino acid compositions of intact protein and peptides (Table 1) and amino acid sequences of intact protein and peptides (Tables 2 and 3) have been deposited as Supplementary Publication SUP 50150 (11 pages) at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms indicated in Biochem. J. (1989) 257, 5.

SUBMITTER: Suzuki T

PROVIDER: S-EPMC1138642 | biostudies-other | 1989 May

REPOSITORIES: biostudies-other

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Project description:The deep-sea tube worm Lamellibrachia, belonging to the Phylum Vestimentifera, contains two giant extracellular haemoglobins, a 3000 kDa haemoglobin and a 440 kDa haemoglobin. The former consists of four haem-containing chains (AI-AIV) and two linker chains (AV and AVI) for the assembly of the haem-containing chains [Suzuki, Takagi & Ohta (1988) Biochem. J. 255, 541-545]. The tube-worm haemoglobins are believed to have a function of transporting sulphide (H2S) to internal bacterial symbionts, as well as of facilitating O2 transport [Arp & Childress (1983) Science 219, 295-297]. We have determined the complete amino acid sequence of Lamellibrachia chain AIII by automated or manual Edman sequencing. The chain is composed of 144 amino acid residues, has three cysteine residues at positions 3, 74 and 133, and has a molecular mass of 16,620 Da, including a haem group. The sequence showed significant homology (30-50% identity) with those of haem-containing chains of annelid giant haemoglobins. Two of the three cysteine residues are located at the positions where an intrachain disulphide bridge is formed in all annelid chains, but the remaining one (Cys-74) was located at a unique position, compared with annelid chains. Since the chain AIII was shown to have a reactive thiol group in the intact 3000 kDa molecule by preliminary experiments, the cysteine residue at position 74 appears to be one of the most probable candidates for the sulphide-binding sites. A phylogenetic tree was constructed from nine chains of annelid giant haemoglobins and one chain of vestimentiferan tube-worm haemoglobin now determined. The tree clearly showed that Lamellibrachia chain AIII belongs to the family of strain A of annelid giant haemoglobins, and that the two classes of Annelida, polychaete and oligochaete, and the vestimentiferan tube worm diverged at almost the same time. H.p.l.c. patterns of peptides (Figs. 4-7), amino acid compositions of peptides (Table 2) and amino acid sequences of intact protein and peptides (Table 3) have been deposited as Supplementary Publication SUP 50154 (13 pages) at the British Library Document Supply Centre, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1990) 265, 5.

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Primary structure of a dimeric haemoglobin from the deep-sea cold-seep clam Calyptogena soyoae.

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