In vivo copper- and cadmium-binding ability of mammalian metallothionein beta domain

The beta domain of mouse metallothionein 1 (beta MT) was synthesized in Esc herichia coil cells grown in the presence of copper or cadmium. Homogenous preparations of Cu-beta MT and Cd-beta MT were used to characterize the cor responding in vivo-conformed metal-clusters, and to compare them with the s pecies obtained in vitro by metal replacement to a canonical Zn-3-beta MT s tructure. The copper-containing beta MT clusters formed inside the cells we re very stable. In contrast, the nascent beta peptide, although it showed c admium binding ability, produced a highly unstable species, whose stoichiom etry depended upon culture conditions, The absence of beta MT protein in E. coli protease-proficient hosts grown in cadmium-supplemented medium pointed to drastic proteolysis of a poorly folded beta peptide, somehow enhanced b y the presence of cadmium. Possible functional and evolutionary implication s of the bioactivity of mammalian beta MT in the presence of monovalent and divalent metal ions are discussed.