Notable diversity in hemoglobin expression patterns among species of the deep-sea clam, Calyptogena

Abstract

The deep-sea clams Calyptogena nautilei and C. tsubasa, which live in the cold-seep area at a depth of 3570 m in the Nankai Trough, Japan, have abundant hemoglobins (Hbs) in erythrocytes, similar to other Calyptogena species. We determined the cDNA-derived amino acid sequences of Hbs from two Calyptogena species. C. tsubasa was found to contain two dimeric Hbs, Hb I consisting of 145 amino acid residues and Hb II with 137 residues, similar to known Hbs from C. soyoae and C. kaikoi. Sequence identity was over 90% among the orthologous chains of Calyptogena Hbs. On the other hand, surprisingly, C. nautilei contained two monomeric Hbs, Hb III containing 141 residues and Hb IV with 134 residues. In addition, Hbs III and IV showed only 33-42% sequence identity with Hbs I and II from other Calyptogena species. The distal (E7) histidine, one of the functionally important residues of the heme protein, is replaced by glutamine in all Hb chains of Calyptogena species. A phylogenetic analysis indicated that C. nautilei Hb III is closer to Hb I from other Calyptogena species. We suppose that a Hb gene was duplicated at least three times in an immediate ancestor of Calyptogena and, presumably depending on physiological conditions different Hb sets are being expressed: dimeric Hbs I and II in C. soyoae, C. kaikoi and C. tsubasa, and monomeric Hbs III and IV in C. nautilei.

Globin’s Structure and Function in Vesicomyid Bivalves from the Gulf of Guinea Cold Seeps as an Adaptation to Life in Reduced Sediments

“…Phreagena soyoae, "Phreagena" tsubasa, and Abyssogena kaikoi (formerly Calyptogena soyoae, Calyptogena tsubasa, and Calyptogena kaikoi; Krylova and Sahling 2010;Audzijonyte et al 2012) all have two homodimeric Hbs of 32 kDa, termed HbI and HbII, with more than 90% sequence identity, revealing their close relationship (Kawano et al 2003). In A. kaikoi both Hbs might also appear as homotetramers, presumably when their concentration is large enough .…”

“…Hemolymphs of all five blood clam species analyzed to date contain intracellular hemoglobin (Hb) in erythrocytes (Terwilliger et al 1983;Suzuki et al 1989aSuzuki et al , 1989bSuzuki and Ohta 2000;Zal et al 2000;Kawano et al 2003). The blood clam "Calyptogena" magnifica Boss & Turner 1980, from the hydrothermal vents on the East Pacific Rise, has an intracellular hemoglobin (Hb) of 68 kDa, which transports oxygen to both host and symbionts (Terwilliger et al 1983;Zal et al 2000), while sulfide is carried by a lipoproteic sulfide-binding component dissolved in the hemolymph (Childress et al 1993;Zal et al 2000).…”

Characterisation of Duplicated Haemoglobin Genes in Bivalves

“…Since all blood clams seem to have originated from a common ancestor, globin structural variations and levels of expression is thought to have been influenced directly by the environmental conditions these clam species are subjected to and specifically oxygen concentration and availability (Kawano et al, 2003). The evidence from this study reinforces that greater expression of Hbs in haemolymph confers a physiological advantage in tolerating hypoxia.…”

“…HbII) in erythrocytes but C. nautilei possess two monomeric Hbs (HbIII and HbIV) which show low sequence identity to HbI and HbII (Kawano et al, 2003). The fourth instance is an extracellular Hb found in the heterodont clams Cardita borealis and C. floridana (Manwell, 1963;Terwilliger et al, 1978).…”

“…For example, the clam C. magnifica is found lodged into rock fissures outside hydrothermal vents and exposed to both deep-sea water and vent fluid meaning that it is frequently subject to chronic hypoxia (Berg, 1980). This species possesses an intracellular Hb with high O 2 affinity for carrying and transport required for its sustainability in such a challenging environment (Terwilliger et al, 1983;Scott & Fisher, 1995;Hourdez & Weber, 2005 (Kawano et al, 2003;Suzuki et al, 2000). Arcid bivalves are also frequently found in habitats with low levels of O 2 such as intertidal zones or deep-sea waters and often experience prolonged periods of hypoxia (Arp et al, 1984;Abele-Oeschger & Oeschger, 1995;Terwilliger, 1998;Weber & Vinogradov, 2001).…”