Structural characterization and thermal stability of Notothenia coriiceps metallothionein

Fish and mammalian metallothioneins (MTs) differ in the amino acid residues placed between their conserved cysteines. We have expressed the MT of an A ntarctic fish, Notothenia coriiceps, and characterized it by means of multi nuclear NMR spectroscopy. Overall, the architecture of the fish MT is very similar to that of mammalian MTs, However, NMR spectroscopy shows that the dynamic behaviour of the two domains is markedly different. With the aid of absorption and CD spectroscopies, we studied the conformational and electr onic features of fish and mouse recombinant Cd-MT and the changes produced in these proteins by heating. When the temperature was increased from 20 to 90 degreesC, the Cd-thiolate chromophore absorbance at 254 nm of mouse MT was not modified up to 60 degreesC, whereas the absorbance of fish MT decre ased significantly starting from 30 degreesC. The CD spectra also changed q uite considerably with temperature, with a gradual decrease of the positive band at 260 nm that was more pronounced for fish than for mouse MT. The di fferential effect of temperature on fish and mouse MTs may reflect a differ ent stability of metal-thiolate clusters of the two proteins. Such a conclu sion is also corroborated by results showing differences in metal mobility between fish and mouse Zn-MT.