Structural and functional studies of vertebrate metallothioneins: Cross-talk between domains in the absence of physical contact

In previous studies, we showed that the chemical and dynamical properties of fish and mouse MT present a number of distinctive differences linked to their primary structure and that phylogenetic relationships of mammal and fish MTs correlate with their three-dimensional structures. The different behavior of MTs may also be linked to the interaction between their two domains. In the present paper, we have compared the physico-chemical properties of the isolated recombinant domains constituting N. coriiceps and mouse MTs, and compared them with those of the corresponding whole MTs. NMR spectra of the separated domains of N. coriiceps are almost superimposable to those of the parent MT, suggesting an apparent lack of interaction between the two domains in the protein. However, certain dynamic and physico-chemical features of the isolated domains are unlike those of the whole protein. In particular, the temperature-induced changes in the chiroptical properties, sulphydryl reactivity of the Zn-MT domains and the Zn 2+/Cd 2+ rate of exchange are different for the two domains and with respect to the whole protein. Taken together, these results provide a strong argument in favor of the interaction of the two domains in the MT molecule, in spite of the elusive evidence brought by the structural analyses.