Investigation of the Copper (Cu) Binding Site on the Amyloid beta 1-16 (Aβ16) Monomer and Dimer Using Collision-induced Dissociation with Electrospray Ionization Tandem Mass Spectrometry

Abstract

The copper ion, Cu(II), binding sites for amyloid fragment AI31-16 (=AI316 ) were investigated to explain the biological activity difference in the AI316 aggregation process. The [M+Cu+(z-2)H](z+) (z = 2, 3 and 4, M = AI316 monomer) and [D+Cu+(z-2)H](z+) (z = 3 and 5, D = AI316 dimer) structures were investigated using electrospray ionization (ESI) mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Fragment ions of the [M+Cu+(z-2)H](z+) and [D+Cu+(z-2)H](z+) complexes were observed using collision-induced dissociation MS/MS. Three different fragmentation patterns (fragment "a", "b", and "y" ion series) were observed in the MS/MS spectrum of the (AI316 monomer or dimer-Cu) complex, with the "b" and "y" ion series regularly observed. The "a" ion series was not observed in the MS/MS spectrum of the [M+Cu+2H](4+) complex. In the non-covalent bond dissociation process, the [D+Cu+3H](5+) complex separated into three components ([M+Cu+H](3+), M3+, and M2+), and the [M+Cu](2+) subunit was not observed. The {M + fragment ion of [M+Cu+H](3+)} fragmentation pattern was observed during the covalent bond dissociation of the [D+Cu +3H](5+) complex. The {M + [M+Cu+H](3+)} complex geometry was assumed to be stable in the [D+Cu+3H](5+) complex. The {M + fragment ion of [M+Cu](2+)} fragmentation pattern was also observed in the MS/MS spectrum of the [D+Cu+H](3+) complex. The {M + [y(9)+Cu](1+)} fragment ion was the characteristic fragment ion. The [D+Cu+H](3+) and [D+Cu+3H](5+)complexes were likely to form a monomer-monomer-Cu (M-M-Cu) structure instead of a monomer-Cu-monomer (M-Cu-M) structure.