NMR structure of the sea urchin (Strongylocentrotus purpuratus) metallothionein MTA

The three-dimensional structure of [Cd-113(7)]-metallothionein-A (MTA) of t he sea urchin Strongylocentrotus purpuratus was determined by homonuclear H -1 NMR experiments and heteronuclear [H-1,Cd-113]-correlation spectroscopy. MTA is composed of two globular domains, an N-terminal four-metal domain o f the amino acid residues 1 to 36 and a Cd(4)Cys(11) cluster, and a C-termi nal three-metal domain including the amino acid residues 37 to 65 and a Cd( 3)Cys(9) cluster. The structure resembles the known mammalian and crustacea n metallothioneins, but has a significantly different connectivity pattern of the Cys-metal co-ordination bonds and concomitantly contains novel local folds of some polypeptide backbone segments. These differences can be rela ted to variations of the Cys sequence positions and thus emphasize the spec ial role of the cysteine residues in defining the structure of metallothion eins, both on the level of the domain architecture and the topology of the metal-thiolate clusters. (C) 1999 Academic Press.