Prion protein and its interactions with metal ions (Cu, Zn, and Cd) and metallothionein 3

The effects of heavy metals (Zn 2+ , Cu 2+ , and/or Cd 2+ ) on Escherichia coli expressing either prion (hPrP C ) or metallothionein 3 (MT-3) brain proteins capable of binding these metals were investigated. The expression of hPrP C or MT-3 in E.coli was confirmed using western-blot and dot-blot methods. After analyzing growth curves, we found that bacteria expressing prion protein better tolerated the presence of Zn 2+ in comparison with wild-type bacteria and bacteria expressing MT-3. The addition of Cd 2+ and Cu 2+ was well tolerated by bacteria expressing MT-3, whereas the bacteria expressing prion protein displayed slower growth when compared to the wild-type. We subsequently determined total content of the MT in bacteria using differential pulsed voltammetry (DPV), and depending on the treatment of the individual metals. MT expression in MT3 transformed cells as well as in control E.coli cells increased at the lowest metal concentration (25 μM), followed by a decrease at higher metal concentrations (50, 75, and 150 μM). The highest increase by Cd 2+ were observed. MT expression pattern in hPrP C transformed cells was different. After application of Cu 2+ an increase in MT expression continued also at higher metal concentrations; and after application of Cd 2+ and Zn 2+ no decrease in MT expression at higher metal concentrations was observed.