title: Cloning and sequencing of cDNAs encoding for a novel copper-specific metallothionein and two cadmium-inducible metallothioneins from the blue crab Callinectes sapidus.
abstract: Metallothioneins (MTs) are cysteine-rich metal-binding proteins found in micro-organisms, plants and all invertebrate and vertebrate animals. Unicellular eukaryotes such as yeast have a copper-MT whose synthesis is induced by a copper-activated transcription factor. Most higher organisms have two major cadmium/zinc MT isoforms, whose synthesis is controlled by a zinc-activated transcription factor. The blue crab, Callinectes sapidus, has two cadmium-inducible isoforms, CdMT-I and CdMT-II, and a third isoform, CuMT-II, which is induced by copper, but not by cadmium. The cDNA sequence of the copper-specific MT, along with those of the two CdMTs, was determined utilizing 3' and 5' rapid amplification of cDNA ends (RACE). CuMT-II cDNA encodes a 63 amino acid protein containing 21 cysteine residues. CdMT-I and CdMT-II cDNA encode a 58 and 57 amino acid protein, respectively, each with 18 cysteines. Molecular phylogeny analysis shows that the CdMT isoforms cluster with other crustacean CdMTs, whereas the copper-specific MT is more closely related to mollusk MTs. CuMT-II shows considerable homology to a copper-specific, non-cadmium inducible, MT from the snail, Helix pomatia. The presence of copper-specific MTs in mollusks and crustaceans, both of which are dependent on hemocyanin for oxygen transport, suggests that CuMT-II is involved in copper homeostasis associated with the synthesis and degradation of hemocyanin.
authors.affiliation: Department of Coastal Sciences, Institute of Marine Sciences, University of Southern Mississippi, 703 East Beach Blvd., Ocean Springs, MS 39564, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Syring
authors.forename: T
authors.initials: T
authors.lastname: Hoexum Brouwer
authors.forename: M
authors.initials: M
authors.lastname: Brouwer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003386:Brachyura / Q000737:chemistry / Q000378:metabolism*; D002104:Cadmium / Q000737:chemistry* / Q000378:metabolism; D003001:Cloning, Molecular; D003300:Copper / Q000737:chemistry* / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D008099:Liver / Q000737:chemistry; D008297:Male; D008668:Metallothionein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D010179:Pancreas / Q000737:chemistry; D010802:Phylogeny; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017385:Sequence Homology
chemical_list: D018076:DNA, Complementary; D020033:Protein Isoforms; D002104:Cadmium; D003300:Copper; D008668:Metallothionein