Metallothionein dimers studied by nano-spray mass spectrometry

Both transient and stable dimers of metallothionein have been characterized, based on earlier studies using NMR, circular dichroism and size-exclusion chromatography. Here additional characterization is provided by nanospray mass spectrometry. Rapid redistribution of metal ions between monomeric Cd-7- and Zn-7-metallothionein 2a is monitored by nanospray. An experiment in which theses two forms of the monomeric protein are separated by a dialysis membrane, which will pass metal ions but not proteins, confirms that a transient dimer must form for metal ions to be redistributed. On the other hand, size-exclusion chromatography of reconstituted Zn-7- or Cd-7-metallothionein revealed the presence of monomeric and dimeric species. These dimers do not equilibrate readily to form monomers and they are shown to be covalent. (C) 2002 Elsevier Science B V All rights reserved.