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Noncooperative cadmium(II) binding to human metallothionein 1a

Authors
Journal
Biochemical and Biophysical Research Communications
0006-291X
Publisher
Elsevier
Publication Date
Volume
372
Issue
4
Identifiers
DOI: 10.1016/j.bbrc.2008.05.142
Keywords
  • Human Metallothionein
  • Metal-Binding Domains
  • Cysteine Redox Chemistry
  • Cooperative Metallation
  • Metal-Induced Protein Folding
  • Partial Metallation
  • Cadmium Binding
  • Zinc Binding
  • Toxic Metal Detoxification
  • Metallation Mechanism
Disciplines
  • Biology

Abstract

Abstract The two-domain (βα) mammalian metallothionein binds seven divalent metals, however, the binding mechanism is not well characterized and recent reports require the presence of the partially metallated protein. In this paper, step-wise metallation of the metal-free, two-domain βα-rhMT and the isolated β-rhMT using Cd(II) is shown to proceed in a noncooperative manner by analysis of electrospray ionization mass spectrometric data. Under limiting amounts of Cd(II), all intermediate metallation states up to the fully metallated Cd 3-β-rhMT and Cd 7-βα-rhMT were observed. Addition of excess Cd(II), resulted in formation of the supermetallated (metallation in excess of normal levels) Cd 4-β- and Cd 8-βα-metallothionein species. These data establish that noncooperative cadmium metallation is a property of each isolated domain and the complete two-domain protein. Our data now also establish that supermetallation is a property that may provide information about the mechanism of metal transfer to other proteins.

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