Interaction of copper-metallothionein from the American lobster, Homarus americanus, with glutathione.
Organisms have harnessed the unique chemistry of copper for a variety of purposes. However, that same chemistry makes this essential metal toxic at elevated concentrations. Metallothioneins (MTs), a family of small metal-binding proteins, are thought to play a crucial role in the regulation of this reactive ion. Here we report that copper-metallothioneins from the American lobster, Homarus americanus, interact with the tripeptide glutathione (gamma-Glu-Cys-Gly). Glutathione in the cytosolic fraction prepared from the digestive gland of the American lobster coelutes with copper-metallothionein during size-exclusion chromatography. The latter protein can be separated into three isoforms by anion-exchange chromatography. All three isoforms belong to the class I MTs. CuMT-I and -II are very similar, whereas CuMT-III is distinct from isoforms I and II. The interaction between glutathione and MT isoforms was examined by ultrafiltration experiments and size-exclusion HPLC. CuMT-III forms a stable 1:1 complex with glutathione, with a dissociation constant of 1 microM. CuMT-I/II makes a transient complex with glutathione, which releases copper as a copper-glutathione complex. This complex can function as the source of Cu(I) in the restoration of the oxygen-binding capacity of copper-free hemocyanin. These studies suggest that metallothionein and glutathione are intricately linked in the biochemistry of copper regulation.
Brouwer
M
M
Duke University Marine Laboratory, Beaufort, North Carolina 28516.
Brouwer-Hoexum
T
T
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003300:Copper / Q000378:metabolism; D004064:Digestive System / Q000378:metabolism; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism*; D006433:Hemocyanins / Q000378:metabolism; D008668:Metallothionein / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D008121:Nephropidae / Q000378:metabolism*
C007121:copper thionein; D003300:Copper; D006433:Hemocyanins; D008668:Metallothionein; D005978:Glutathione