Single domain metallothioneins: supermetalation of human MT 1a.

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Sutherland DE, Willans MJ, Stillman MJ

Single domain metallothioneins: supermetalation of human MT 1a.

J Am Chem Soc. 2012 Feb 15;134(6):3290-9. doi: 10.1021/ja211767m. Epub 2012 Feb 6.

PubMed ID

22242602 [ View in PubMed

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Abstract

Metallothioneins are a family of small, cysteine rich proteins that have been implicated in a range of roles including toxic metal detoxification, protection against oxidative stress, and as metallochaperones involved in the homeostasis of both essential zinc and copper. We report that human metallothionein 1a, well-known to coordinate 7 Zn(2+) or Cd(2+) ions with 20 cysteinyl thiols, will bind 8 structurally significant Cd(2+) ions, leading to the formation of the supermetalated Cd(8)-betaalpha-rhMT 1a species, for which the structure is a novel single domain. ESI-mass spectrometry was used to determine the exact metalation status of the betaalpha-rhMT. The derivative-shaped CD envelope of Cd(7)-betaalpha-rhMT [peak extrema (+) 260 and (-) 239 nm] changed drastically upon formation of the Cd(8)-betaalpha-rhMT with the appearance of a sharp monophasic CD band centered on 252 nm, a feature indicative of the loss of cluster symmetry. The structural significance of the eighth Cd(2+) ion was determined from a combination of direct and indirect (113)Cd nuclear magnetic resonance (NMR) spectra. In the case of Cd(8)-betaalpha-rhMT, only four peaks were observed in the direct (113)Cd NMR spectrum. Significantly, while both of the isolated domains can be supermetalated forming Cd(4)-beta-rhMT and Cd(5)-alpha-rhMT, Cd(8)-betaalpha-rhMT and not Cd(9)-betaalpha-rhMT was observed following addition of excess Cd(2+). We propose that both domains act in concert to coordinate the eighth Cd(2+) atom, and furthermore that this interaction results in a coalescence of the two domains leading to collapse of the two-domain structure. This is the first report of a possible single-"superdomain" metallothionein structure for Zn(2+) and Cd(2+) binding mammalian proteins. A computational model of a possible single-domain structure of Cd(8)-betaalpha-rhMT is described.

DrugBank Data that Cites this Article

Drug Targets

Drug	Target	Kind	Organism	Pharmacological Action	Actions
Zinc	Metallothionein-1A	Protein	Humans	Unknown	Not Available	Details
Zinc acetate	Metallothionein-1A	Protein	Humans	Unknown	Not Available	Details
Zinc chloride	Metallothionein-1A	Protein	Humans	Unknown	Binder	Details
Zinc sulfate, unspecified form	Metallothionein-1A	Protein	Humans	Unknown	Binder	Details