title: Physiological relevance and contribution to metal balance of specific and non-specific Metallothionein isoforms in the garden snail, Cantareus aspersus.
abstract: Variable environmental availability of metal ions represents a constant challenge for most organisms, so that during evolution, they have optimised physiological and molecular mechanisms to cope with this particular requirement. Metallothioneins (MTs) are proteins that play a major role in metal homeostasis and as a reservoir. The MT gene/protein systems of terrestrial helicid snails are an invaluable model for the study of metal-binding features and MT isoform-specific functionality of these proteins. In the present study, we characterised three paralogous MT isogenes and their expressed products in the escargot (Cantareus aspersus). The metal-dependent transcriptional activation of the three isogenes was assessed using quantitative Real Time PCR. The metal-binding capacities of the three isoforms were studied by characterising the purified native complexes. All the data were analysed in relation to the trace element status of the animals after metal feeding. Two of the three C.                         aspersus MT (CaMT) isoforms appeared to be metal-specific, (CaCdMT and CaCuMT, for cadmium and copper respectively). A third isoform (CaCd/CuMT) was non-specific, since it was natively recovered as a mixed Cd/Cu complex. A specific role in Cd detoxification for CaCdMT was revealed, with a 80-90% contribution to the Cd balance in snails exposed to this metal. Conclusive data were also obtained for the CaCuMT isoform, which is involved in Cu homeostasis, sharing about 30-50% of the Cu balance of C. aspersus. No apparent metal-related physiological function was found for the third isoform (CaCd/CuMT), so its contribution to the metal balance of the escargot may be, if at all, of only marginal significance, but may enclose a major interest in evolutionary studies.
authors.affiliation: Institute of Zoology, University of Innsbruck, Innsbruck, Austria.
authors.forename: Martina
authors.initials: M
authors.lastname: Höckner
authors.forename: Karin
authors.initials: K
authors.lastname: Stefanon
authors.forename: Annette
authors.initials: A
authors.lastname: de Vaufleury
authors.forename: Freddy
authors.initials: F
authors.lastname: Monteiro
authors.forename: Sílvia
authors.initials: S
authors.lastname: Pérez-Rafael
authors.forename: Oscar
authors.initials: O
authors.lastname: Palacios
authors.forename: Mercè
authors.initials: M
authors.lastname: Capdevila
authors.forename: Sílvia
authors.initials: S
authors.lastname: Atrian
authors.forename: Reinhard
authors.initials: R
authors.lastname: Dallinger
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002104:Cadmium / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003300:Copper / Q000378:metabolism*; D006372:Helix, Snails / Q000033:anatomy & histology / Q000235:genetics / Q000378:metabolism*; D013058:Mass Spectrometry / Q000379:methods; D008668:Metallothionein / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D014158:Transcription, Genetic
chemical_list: D020033:Protein Isoforms; D011994:Recombinant Proteins; D002104:Cadmium; D003300:Copper; D008668:Metallothionein