title: Metagenomics analysis reveals a new metallothionein family: Sequence and metal-binding features of new environmental cysteine-rich proteins.
abstract: Metallothioneins are cysteine-rich proteins, which function as (i) metal carriers in basal cell metabolism and (ii) protective metal chelators in conditions of metal excess. Metallothioneins have been characterized from different eukaryotic model and cultivable species. Presently, they are categorized in 15 families but evolutionary relationships between these metallothionein families remain unresolved. Several cysteine-rich protein encoding genes that conferred Cd-tolerance in Cd-sensitive yeast mutants have previously been isolated from soil eukaryotic metatranscriptomes. They were called CRPs for "cysteine-rich proteins". These proteins, of unknown taxonomic origins, share conserved cysteine motifs and could be considered as metallothioneins. In the present work, we analyzed these CRPs with respect to their amino acid sequence features and their metal-binding abilities towards Cd, Zn and Cu metal ions. Sequence analysis revealed that they share common features with different known metallothionein families, but also exhibit unique specific features. Noticeably, CRPs display two separate cysteine-rich domains which, when expressed separately in yeast, confer Cd-tolerance. The N-terminal domain contains some conserved atypical Cys motifs, such as one CCC and two CXCC ones. Five CRPs were expressed and purified as recombinant proteins and their metal-binding characteristics were studied. All these CRPs chelated Cd(II), Zn(II) and Cu(I), although displaying a better capacity for Zn(II) coordination. All CRPs are able to confer Cd-tolerance, and four of them confer Zn-tolerance in the Zn-sensitive zrc1Δ yeast mutant. We designated these CRPs as environmental metallothioneins belonging to a new formerly undescribed metallothionein family.
authors.affiliation: Microbial Ecology, CNRS UMR 5557, INRA UMR 1418, Université Lyon 1, Université de Lyon, F-69622 Villeurbanne, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Ziller
authors.affiliation: Microbial Ecology, CNRS UMR 5557, INRA UMR 1418, Université Lyon 1, Université de Lyon, F-69622 Villeurbanne, France.
authors.forename: Rajiv Kumar
authors.initials: RK
authors.lastname: Yadav
authors.affiliation: Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Barcelona, Spain.
authors.forename: Mercè
authors.initials: M
authors.lastname: Capdevila
authors.affiliation: Thapar University, Department of Biotechnology, Bhadson Road, Patiala 147 004, India.
authors.forename: Mondem Sudhakara
authors.initials: MS
authors.lastname: Reddy
authors.affiliation: Microbial Ecology, CNRS UMR 5557, INRA UMR 1418, Université Lyon 1, Université de Lyon, F-69622 Villeurbanne, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Vallon
authors.affiliation: Microbial Ecology, CNRS UMR 5557, INRA UMR 1418, Université Lyon 1, Université de Lyon, F-69622 Villeurbanne, France.
authors.forename: Roland
authors.initials: R
authors.lastname: Marmeisse
authors.affiliation: Departament de Genètica, Microbiologia i Estadística, Facultat de Biologia, Universitat de Barcelona, Av. Diagonal 643, E-08028 Barcelona, Spain.
authors.forename: Silvia
authors.initials: S
authors.lastname: Atrian
authors.affiliation: Departament de Química, Facultat de Ciències, Universitat Autònoma de Barcelona, E-08193 Cerdanyola del Vallès, Barcelona, Spain.
authors.forename: Òscar
authors.initials: Ò
authors.lastname: Palacios
authors.affiliation: Microbial Ecology, CNRS UMR 5557, INRA UMR 1418, Université Lyon 1, Université de Lyon, F-69622 Villeurbanne, France. Electronic address: fraissin@univ-lyon1.fr.
authors.forename: Laurence
authors.initials: L
authors.lastname: Fraissinet-Tachet
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D054892:Metagenome; D056186:Metagenomics; D008668:Metallothionein / Q000737:chemistry / Q000235:genetics; D019216:Metals, Heavy / Q000737:chemistry*; D008969:Molecular Sequence Data
chemical_list: D019216:Metals, Heavy; D008668:Metallothionein
keywords: Cysteine-rich protein; Environmental genomics; Metal-binding protein; Metallothionein; Metatranscriptomics