Molecular cloning and evolution of lobster hemocyanin.
In the American lobster, Homarus americanus, oxygen is transported by a hemocyanin that is composed 2 x 6 subunits. N-terminal sequencing show the presence of three distinct subunit types (alpha, beta and gamma). We cloned the cDNA of one of these subunits that belong to the alpha-type. It encodes a hemocyanin subunit of 654 amino acids with a molecular mass of 84.8 kDa, which is synthesized in the hepatopancreas. Phylogenetic analyses of the crustacean hemocyanin sequences show two well-separated clades, which correspond to the alpha and gamma-type subunits. Sequences of beta-type subunits are still unknown. The gamma-sequences have evolved about 15% faster than the alpha-subunits, consistent with the proposed conservative function of the latter. Under the assumption of a molecular clock we calculated that alpha- and gamma-subunits split about 214 +/- 14 million years ago, suggesting their divergence only in the decapod Crustacea.
Kusche
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Institute of Zoology, University of Mainz, Müllerweg 6, Mainz, D-55099, Germany.
Burmester
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T
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D006433:Hemocyanins / Q000096:biosynthesis / Q000235:genetics*; D008969:Molecular Sequence Data; D008121:Nephropidae / Q000235:genetics*; D010802:Phylogeny; D021122:Protein Subunits; D012333:RNA, Messenger / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution
D021122:Protein Subunits; D012333:RNA, Messenger; C427483:hemocyanin A, lobster; D006433:Hemocyanins