Metal-Metallothionein complexes: insights into structural features by Raman spectroscopy.

Metallothioneins (MTs) are low molecular weight, cysteine-rich proteins with an exceptional heavy metal coordination capacity. Because of their ability to bind metals and to scavenge oxidant radicals, MTs are considered to play a role in metal homeostasis, metal detoxificalion and control of the oxidative stress. Although their high heterogeneity on the expression patterns, metal binding abilities and primary structure suggest very diverse functional specializations, the structural and functional studies have been mainly devoted to vertebrate and fungal MTs. Participation of metal ligands other than the cysteines and the presence of secondary structure elements in metal-MT complexes are fairly unknown, especially in non-vertebrate MTs. Recently, it has been shown that ligands other than Cys can participate in the coordination sphere of metals in MTs. Two main types have been identified: endogenous ligands such as imidazole moiety of His residues and /or exogenous ligands such as inorganic ions (i.e. sulfide or chloride ions).