Binding of excess cadmium(II) to Cd-7-metallothionein from recombinant mouse Zn-7-metallothionein 1. UV-VIS absorption and circular dichroism studies and theoretical location approach by surface accessibility analysis

作者：Cols N; RomeroIsart N; Capdevila M; Oliva B; GonzalezDuarte P; GonzalezDuarte R; Atrian S

来源：Journal of Inorganic Biochemistry, 1997, 68(3): 157-166.

DOI：10.1016/S0162-0134(97)00085-8

A mouse metallothionein (MT) 1 expression system has been constructed that renders recombinant MT as a high parity Zn-coordinated protein. Spectral changes in absorption and circular dichroism following the addition of up to 7 mol equivalents of Cd2+ to recombinant Zn-7-MT showed that it behaves like the native protein. Exposure of Cd-7-MT to Cd2+ resulted in further binding of these ions to the protein, although saturation was not achieved on the addition of up to 22 mol equivalents of Cd2+ to Zn-7-MT. Spectral data are compatible with a model in which the first four additional Cd ions are bound to Cd-7-MT via sulfur atoms, and indicate that no further thiol groups are involved in the binding of the excess Cd(II) over 11. Cd2+ ions bound in excess to Cd-7-MT appear to have lower binding constants as exposure of Cd-n-MT (n > 7) species to Chelex-100 retrieved Cd-7-MT. Based on the X-ray data, the accessible surface areas of sulfur atoms in Cd-5, Zn-2-MT 2 were calculated. This led us to propose that the coordination of the first three additional Cd(II) ions to Cd-7-MT proceeds by means of S-Met1-0-Met1, S-Cys7-S-Cys13 and S-Cys5-S-Cys26 pairs. Finally, comparison of the behavior of the entire MT with that of the recombinant alpha MT and beta MT subunits indicates that mutual influences may not be negligible.

• 出版日期1997-11-15