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Protein and metal cluster structure of the wheat metallothionein domain -Ec-1: the second part of the puzzle

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2011
Author Loebus Jens, Peroza Estevao A., Blüthgen Nancy, Fow Thomas, Meyer-Klaucke Wolfram, Zerbe Oliver, Freisinger Eva,
Project A. Structures and properties of plant metallothioneins and related artificial proteins - B. Site specific modifications of larger nucleic acids
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Original article (peer-reviewed)

Journal J. Biol. Inorg. Chem.
Volume (Issue) 16
Page(s) 683 - 694
Title of proceedings J. Biol. Inorg. Chem.
DOI 10.1007/s00775-011-0770-2

Abstract

Metallothioneins (MTs) are small cysteine-rich proteins coordinating various transition metal ions, including ZnII, CdII, and CuI. MTs are ubiquitously present in all phyla, indicating a successful molecular concept for metal ion binding in all organisms. The plant MT Ec-1 from Triticum aestivum, common bread wheat, is a ZnII- binding protein that comprises two domains and binds up to six metal ions. The structure of the C-terminal four metal ion binding bE domain was recently described. Here we present the structure of the N-terminal second domain, c-Ec-1, determined by NMR spectroscopy. The c-Ec-1 domain enfolds an M2 IICys6 cluster and was characterized as part of the full-length Zn6Ec-1 protein as well as in the form of the separately expressed domain, both in the ZnII- containing isoform and the CdII-containing isoform. Extended X-ray absorption fine structure analysis of Zn2c- Ec-1 clearly shows the presence of a ZnS4 coordination sphere with average Zn–S distances of 2.33 A ° . 113Cd NMR experiments were used to identify the MII-Cys connectivity pattern, and revealed two putative metal cluster conformations. In addition, the general metal ion coordination abilities of c-Ec-1 were probed with CdII binding experiments as well as by pH titrations of the ZnII and CdII forms, the latter suggesting an interaction of the c domain and the bE domain within the full-length protein.
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