Portal de Periódicos da CAPES

Brain-Specific Metallothionein-3 Has Higher Metal-Binding Capacity than Ubiquitous Metallothioneins and Binds Metals Noncooperatively

2002; American Chemical Society; Volume: 41; Issue: 19 Linguagem: Inglês

10.1021/bi025664v

1943-295X

Peep Palumaa, Elo Eriste, Olga Njunkova, Lesja Pokras, Hans Jörnvall, Rannar Sillard,

Alzheimer's disease research and treatments

Zinc metabolism in the cells is largely regulated by ubiquitous small proteins, metallothioneins (MT). Metallothionein-3 is specifically expressed in the brain and is down regulated in Alzheimer's disease. We demonstrate by mass spectrometry that MT-3, in contrast to common MTs, binds Zn2+ and Cd2+ in a noncooperative manner and can also bind higher stoichiometries of metals than seven. MT-3 reconstituted with seven metals exists in a dynamic equilibrium of different metalloforms, where the prevalent metalloform is Me7MT-3, but metalloforms with 6, 8, and even 9 metals are also present. The results from pH and stability studies demonstrate that the heterogeneity of metalloforms originates from the N-terminal β-cluster, whereas the C-terminal α-cluster of MT-3 binds four metal ions such as that of common MTs. Experiments with EDTA demonstrate that the β-cluster of ZnMT-3 has a higher metal transfer potential than the β-cluster of Zn7MT-2. Moreover, ZnMT-3 loses metals during ultrafiltration. MT-3, reconstituted with an excess of Zn2+ or Cd2+, exists as a dynamic mixture of metalloforms with higher than 7 metal stoichiometries (8−11). Such forms of ZnMT-3 are unstable and decompose partly already during a rapid gel filtration, whereas CdMT-3 forms are more stable. Extra metal ions may bind to the β-cluster region as well as to the carboxylates of MT-3. The specific metal-binding properties of MT-3 could be functionally implemented for buffering of fluctuating concentrations of zinc in zincergic neurons and for transfer of zinc to synaptic vesicles.