Solution structure of MT-nc, a novel metallothionein from the Antarctic fish Notothenia coriiceps

The structure of [Cd-113(7)]-metallothionein (MT_nc)of the Antarctic fish Notothenia coriiceps, the first three-dimensional structure of a fish metallothionein, was determined by homonuclear H-1 NMR experiments and heteronuclear [H-1, Cd-113]-correlation spectroscopy. MT_nc is composed of an N-terminal beta domain with 9 cysteines and 3 metal ions and a carboxy-terminal alpha-domain with I I cysteines and 4 metal ions. The position of the ninth Cys of the alpha domain of MT_nc is different from the corresponding Cys of mammalian MTs. As a result, the last CXCC motif in the mammalian MT sequence becomes CXXXCC in the fish MT. This difference leads to a structural change of the alpha domain and, in turn, to a different charge distribution with respect to that observed in mammalian metallothioneins.