Prion protein and its interactions with metal ions (Cu2+, Zn2+, and Cd2+) and metallothionein 3

Abstract

The effects of heavy metals (Zn2+, Cu2+, and/or Cd2+) on Escherichia coli expressing either prion (hPrPC ) or metallothionein 3 (MT-3) brain proteins capable of binding these metals were investigated. The expression of hPrPC 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 Zn2+ in comparison with wild-type bacteria and bacteria expressing MT-3. The addition of Cd2+ and Cu2+ 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 Cd2+ were observed. MT expression pattern in hPrPC transformed cells was different. After application of Cu2+ an increase in MT expression continued also at higher metal concentrations; and after application of Cd2+ and Zn2+ no decrease in MT expression at higher metal concentrations was observed.