Suppression of Copper-Induced Cellular Damage by Copper Sequestration with S100b Protein

We previously reported that S100b protein (homodimer of S100β subunit) can bind copper ions with a submicromolar dissociation constant (T. Nishikawaet al., J. Biol. Chem.272, 23037–23041, 1997). In this study, a question was addressed as to whether this protein can sequester copper ions in anin vivosituation.Escherichia colicells that had been rendered able to produce a fusion protein of rat S100β subunit with glutathioneS-transferase displayed a marked resistance to cellular damage induced by copper alone or its combination with H2O2, compared with control cells expressing the transferase moiety only. A study by gel chromatography showed that about half of the expressed S100β fusion protein in the cytosol of copper-treated cells was eluted in the void volume fraction (molecular mass > 200 kDa), which contained most of the copper incorporated. The S100β fusion protein purified from the void volume fraction was found to contain 82% of the total copper in the fraction, while in a parallel experiment with the control cells, the glutathioneS-transferase eluted in the void volume fraction contained only 18% of the total copper. Thus, it is clear that extraneously expressed S100b protein can acts as a “copper sink,” thereby protectingE. colicells from copper-induced cellular damage.