Metallothioneins are characterized as a group of small proteins with low molecular weight and high content of cysteinyl residues and their synthesis is induced by metal ions (e.g., Zn or Cd). The physicochemical properties of Zn-, Cd-, and Cu-containing MTs have been studied. However, copper metallothioneins (CuOMTs) have been examined less intensively, with only two MTs containing Cu(I) having been structurally characterized to date i.e., yeast MT and Neurospora crassa MT. The present study focuses on the stoichiometry and structural effects of binding of Cu(I) to the natively zinc binding MT (SmtA) from the cyanobacterium Synechococcus elongatus PCC7942. For this purpose, a Cu(I) titration study of Zn4SmtA was anaerobically performed utilizing the collective detection of ESIOMS, UV-Vis absorbance and 1H-15N NMR spectroscopy, and fully exchanged Cu(I)-SmtA was also generated from the apoOprotein. ESIOMS data confirmed the presence of predominantly monomeric Cu7SmtA. UV-vis titrations of Zn4SmtA showed that up to 7 Cu(I) displace Zn(II) from the protein, which was further studied in more detail by Cu(I) titrations of Zn4SmtA monitored with 1H-15N and 111Cd-15H NMR spectroscopy. The extensive NMR analysis showed the unfolding of protein on Cu(I) addition with absence of inertness towards Cu(I) exchange and that the protein undergoes significant conformational changes on Cu(I) addition. Preliminary characterization of MymT from Mycobacterium tuberculosis was also done and the composition of the metal cluster in the dominant Cu5MymT species was proposed and cooperativity was established by ESIOMS analyses, although structural characterisation was impeded by the highly dynamic nature of the protein.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:635621 |
| Date | January 2014 |
| Creators | Tareen, Maria |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/66365/ |
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