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Shaping mechanisms of metal specificity in a family of metazoan metallothioneins : evolutionary differentiation of mollusc metallothioneins
Palacios Bonilla, Òscar (Universitat Autònoma de Barcelona. Departament de Química)
Pagani, Ayelen (Universitat de Barcelona. Departament de Genètica)
Pérez Rafael, Sílvia (Universitat Autònoma de Barcelona. Departament de Química)
Egg, Margit (University of Innsbruck. Institute of Zoology and Center of Molecular Biosciences)
Höckner, Martina (University of Innsbruck. Institute of Zoology and Center of Molecular Biosciences)
Brandstätter, Anita (Innsbruck Medical University. Department of Medical Genetics)
Capdevila Vidal, Mercè (Universitat Autònoma de Barcelona. Departament de Química)
Atrian i Ventura, Sílvia (Universitat de Barcelona. Departament de Genètica)
Dallinger, Reinhard (University of Innsbruck. Institute of Zoology and Center of Molecular Biosciences)

Data: 2011
Resum: Background: The degree of metal binding specificity in metalloproteins such as metallothioneins (MTs) can be crucial for their functional accuracy. Unlike most other animal species, pulmonate molluscs possess homometallic MT isoforms loaded with Cu+ or Cd2+. They have, so far, been obtained as native metal-MT complexes from snail tissues, where they are involved in the metabolism of the metal ion species bound to the respective isoform. However, it has not as yet been discerned if their specific metal occupation is the result of a rigid control of metal availability, or isoform expression programming in the hosting tissues or of structural differences of the respective peptides determining the coordinative options for the different metal ions. In this study, the Roman snail (Helix pomatia) Cu-loaded and Cd-loaded isoforms (HpCuMT and HpCdMT) were used as model molecules in order to elucidate the biochemical and evolutionary mechanisms permitting pulmonate MTs to achieve specificity for their cognate metal ion. Results: HpCuMT and HpCdMT were recombinantly synthesized in the presence of Cd2+, Zn2+ or Cu2+ and corresponding metal complexes analysed by electrospray mass spectrometry and circular dichroism (CD) and ultra violet-visible (UV-Vis) spectrophotometry. Both MT isoforms were only able to form unique, homometallic and stable complexes (Cd6-HpCdMT and Cu12-HpCuMT) with their cognate metal ions. Yeast complementation assays demonstrated that the two isoforms assumed metal-specific functions, in agreement with their binding preferences, in heterologous eukaryotic environments. In the snail organism, the functional metal specificity of HpCdMT and HpCuMT was contributed by metal-specific transcription programming and cell-specific expression. Sequence elucidation and phylogenetic analysis of MT isoforms from a number of snail species revealed that they possess an unspecific and two metal-specific MT isoforms, whose metal specificity was achieved exclusively by evolutionary modulation of non-cysteine amino acid positions. Conclusion: The Roman snail HpCdMT and HpCuMT isoforms can thus be regarded as prototypes of isoform families that evolved genuine metal-specificity within pulmonate molluscs. Diversification into these isoforms may have been initiated by gene duplication, followed by speciation and selection towards opposite needs for protecting copper-dominated metabolic pathways from nonessential cadmium. The mechanisms enabling these proteins to be metal-specific could also be relevant for other metalloproteins.
Ajuts: Ministerio de Ciencia e Innovación BIO2009-12513-C02-01
Ministerio de Ciencia e Innovación BIO2009-12513-C02-02
Agència de Gestió d'Ajuts Universitaris i de Recerca 2014/SGR-1457
Drets: Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original. Creative Commons
Llengua: Anglès
Document: Article ; recerca ; Versió publicada
Publicat a: BMC biology, Vol. 9, Núm. 4 (January 2011) , p. 1-20, ISSN 1741-7007

DOI: 10.1186/1741-7007-9-4
PMID: 21255385

20 p, 2.3 MB

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