Localization and Spectroscopic Analysis of the Cu(I) Binding Site in Wheat Metallothionein E sub(c)-1

• Published in: International journal of molecular sciences 2016-03, Vol.17 (3), p.371-371
• Main Authors: Tarasava, Katsiaryna, Loebus, Jens, Freisinger, Eva
• Format: Article
• Language: English
• Subjects: Triticum; Triticum aestivum
• ISSN: 1422-0067
• DOI: 10.3390/ijms17030371

The early cysteine-labeled metallothionein (MT) from Triticum aestivum(common wheat), denoted E sub(c)-1, features two structurally well-defined domains, gamma and beta sub(E), coordinating two and four Zn(II) ions, respectively. While the protein is currently assumed to function mainly in zinc homeostasis, a low amount of copper ions was also recently detected in a native E sub(c)-1 sample. To evaluate the observed copper binding in more detail, the recombinant Zn sub(6) E sub(c)-1 form was exposed to different amounts of Cu(I) ions and the resulting species characterized with spectroscopic methods. Data reveal that the first Cu(I) equivalent coordinates exclusively to the N-terminal gamma -domain of the protein and replaces one Zn(II) ion. To analyze the ability of the gamma -domain for coordination of monovalent metal ions in more detail, the gamma -E sub(c)-1 peptide fragment was incubated with increasing amounts of Cu(I) and the process monitored with UV-VIS, circular dichroism, and luminescence spectroscopy. Closely similar spectra are observed regardless if the apo- or the metal ion-loaded and, hence, pre-folded forms, were used for the titration experiments with Cu(I). The results indicate that low amounts of Cu(I) ions displace the two metal ions subsequently and stoichiometrically, despite the different coordination geometry requirements of Cu(I) and Zn(II).