The sequence of a gastropod hemocyanin (HtH1 from Haliotis tuberculata).
The eight functional units (FUs), a-h, of the hemocyanin isoform HtH1 from Haliotis tuberculata (Prosobranchia, Archaeogastropoda) have been sequenced via cDNA, which provides the first complete primary structure of a gastropod hemocyanin subunit. With 3404 amino acids (392 kDa) it is the largest polypeptide sequence ever obtained for a respiratory protein. The cDNA comprises 10,758 base pairs and includes the coding regions for a short signal peptide, the eight different functional units, a 3'-untranslated region of 478 base pairs, and a poly(A) tail. The predicted protein contains 13 potential sites for N-linked carbohydrates (one for HtH1-a, none for HtH1-c, and two each for the other six functional units). Multiple sequence alignments show that the fragment HtH1-abcdefg is structurally equivalent to the seven-FU subunit from Octopus hemocyanin, which is fundamental to our understanding of the quaternary structures of both hemocyanins. Using the fossil record of the gastropod-cephalopod split to calibrate a molecular clock, the origin of the molluscan hemocyanin from a single-FU protein was calculated as 753 +/- 68 million years ago. This fits recent paleontological evidence for the existence of rather large mollusc-like species in the late Precambrian.
Lieb
B
B
Institute of Zoology, Johannes Gutenberg University of Mainz, D-55099 Mainz, Germany.
Altenhein
B
B
Markl
J
J
D000595:Amino Acid Sequence; D000818:Animals; D003198:Computer Simulation; D018076:DNA, Complementary / Q000378:metabolism; D019143:Evolution, Molecular; D015723:Gene Library; D006433:Hemocyanins / Q000031:analogs & derivatives* / Q000737:chemistry / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008974:Mollusca / Q000737:chemistry* / Q000235:genetics; D049831:Octopodiformes / Q000737:chemistry; D010802:Phylogeny; D011485:Protein Binding; D020033:Protein Isoforms; D017386:Sequence Homology, Amino Acid
D018076:DNA, Complementary; D020033:Protein Isoforms; C121185:hemocyanin type 1, abalone; D006433:Hemocyanins