A protein-sequence similarity insight into the Zn requirement for the in vivo folding of copper metallothioneins

Metallothioneins (MT) are small proteins with a high Cys content, characterised by their extreme ability to bind both essential -Zn(II) and Cu(I)- and toxic -Cd(II) and Hg(II)- heavy metal ions. Structural analysis of Homarus americanus
MT (MTH) and its two [3]3MTH and [3ccMTH domains by recombinant synthesis in E.coli cells grown in Zn- and Cusupplemented media J, has led to the conclusion that MTH requires the presence of Zn(II) in Cu-MT species folded in
vivo. This metal binding behaviour is similar to that of mouse MT1 and its cc fragment 2, and different from Drosophila MTN 3 and the 13 fragment of mouse MT1 4, whose in-vivo-folded copper clusters do not include zinc. By using a proteinsequence similiraty approach (ClustalW) we obtained a multiple sequence alignment for Arthropoda MT peptides, also including the yeast copper-MT(CUP1). Tree constructed from sequence distances, measured by Protdist-Fitch (Phylip)
showed that protein sequences with the same metal preferences clustered together, independently of the taxonomic situation of the corresponding organisms. These results constitute the first attempt to reveal MT sequence constraints
associatted to the preferent chelation of a given physiological metal.