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

In previous studies, we showed that the chem. and dynamic properties of fish and mouse MTs (metallothioneins) present a no. of distinctive differences linked to their primary structures, and that phylogenetic relationships of mammal and fish MTs correlate with their three-dimensional structures. The different behaviors of MTs may also be linked to the interaction between their two domains. In the present study, we have compared the physicochem. properties of the isolated recombinant domains constituting Notothenia coriiceps and mouse MTs, and compared them with those of the corresponding whole MTs. NMR spectra of the sepd. domains of N. coriiceps are almost superimposable on those of the parent MT, suggesting an apparent lack of interaction between the two domains in the protein. However, certain dynamic and physicochem. features of the isolated domains are unlike those of the whole protein. In particular, the temp.-induced changes in the chiroptical properties, thiol reactivity of the Zn-MT domains and the Zn2+/Cd2+ 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 mol., in spite of the elusive evidence provided by the structural analyses.