Copper Transporters? Glutathione Reactivity of Products of Cu-Aβ Digestion by Neprilysin.

Aβ is the major subspecies of Aβ peptides characterized by avid Cu(II) binding via the ATCUN/NTS motif. It is thought to be produced proteolytically by neprilysin, but experiments in the presence of Cu(II) ions indicated preferable formation of C-terminally truncated ATCUN/NTS species including CuAβ, CuAβ, and also CuAβ, all with nearly femtomolar affinities at neutral pH. Such small complexes may serve as shuttles for copper clearance from extracellular brain spaces, on condition they could survive intracellular conditions upon crossing biological barriers. In order to ascertain such possibility, we studied the reactions of CuAβ, CuAβ, CuAβ, and CuAβ with reduced glutathione (GSH) under aerobic and anaerobic conditions using absorption spectroscopy and mass spectrometry. We found CuAβ and CuAβ to be strongly resistant to reduction and concomitant formation of Cu(I)-GSH complexes, with reaction times ∼10 h, while CuAβ was reduced within minutes and CuAβ within seconds of incubation. Upon GSH exhaustion by molecular oxygen, the CuAβ complexes were reformed with no concomitant oxidative damage to peptides. These finding reinforce the concept of Aβ peptides as physiological trafficking partners of brain copper.