Metal Ion Binding to the Amyloid β Monomer Studied by Native Top-Down FTICR Mass Spectrometry

Abstract

Native top-down mass spectrometry is a fast, robust biophysical technique that can provide molecular-scale information on the interaction between proteins or peptides and ligands, including metal cations. Here we have analyzed complexes of the full-length amyloid β (1-42) monomer with a range of (patho)physiologically relevant metal cations using native Fourier transform ion cyclotron resonance mass spectrometry and three different fragmentation methods—collision-induced dissociation, electron capture dissociation, and infrared multiphoton dissociation—all yielding consistent results. Amyloid β is of particular interest as its oligomerization and aggregation are major events in the etiology of Alzheimer’s disease, and it is known that interactions between the peptide and bioavailable metal cations have the potential to significantly damage neurons. Those metals which exhibited the strongest binding to the peptide (Cu2+, Co2+, Ni2+) all shared a very similar binding region containing two of the histidine residues near the N-terminus (His6, His13). Notably, Fe3+ bound to the peptide only when stabilized toward hydrolysis, aggregation, and precipitation by a chelating ligand, binding in the region between Ser8 and Gly25. We also identified two additional binding regions near the flexible, hydrophobic C-terminus, where other metals (Mg2+, Ca2+, Mn2+, Na+, and K+) bound more weakly—one centered on Leu34, and one on Gly38. Unexpectedly, collisional activation of the complex formed between the peptide and [CoIII(NH3)6]3+ induced gas-phase reduction of the metal to CoII, allowing the peptide to fragment via radical-based dissociation pathways. This work demonstrates how native mass spectrometry can provide new insights into the interactions between amyloid β and metal cations. Electronic supplementary materialThe online version of this article (10.1007/s13361-019-02283-7) contains supplementary material, which is available to authorized users.

Metal ions shape α-synuclein

“…This illustrates the difficulty of predicting protein-metal ion interactions, particularly for a protein with an undefined structure and the need for more insight into these molecular mechanisms. There are also promising top-down MS/MS fragmentation approaches which can identify binding sites of metal ions in proteins, namely electron transfer dissociation (ETD), electron capture dissociation (ECD) and ultraviolet photodissociation (UVPD), but the challenge here is that the fragment-level binding data should be linked with a specific conformational state of the protein 45,80 .…”

A Probeless Capacitive Biosensor for Direct Detection of Amyloid Beta 1-42 in Human Serum Based on an Interdigitated Chain-Shaped Electrode

“…The direct detection of aβ with no redox probe is performed by non-Faradaic capacitive measurement, which is greatly different from the Faradaic measurement of the charge transfer resistance of the redox probe. The novelty and difference of non-Faradaic capacitive measurement in this report, as compared to the impedance detection of the charge transfer redox probe couple, in previous studies including our article [ 18 , 20 , 27 , 33 ], is the direct detection of aβ with no redox probe, which can avoid the denaturation of protein caused by the metallization (binding of aβ to metal ion Fe which is presented in the redox couple) [ 29 , 30 , 31 ].…”

“…In contrast with the Faradaic detection of aβ (with the presence of a redox probe couple (Fe(CN) 6 ) 3-/4- in phosphate buffer saline), using the change of the charge-transfer resistance as a parameter for the detection in the recent publication [ 27 ], the non-Faradaic detection of aβ is the direct detection in only phosphate buffer saline (PBS, pH 7.4) solution (without the addition of any redox probe couple (Fe(CN) 6 ) 3−/4− ) is the sensing mechanism, and the change in interfacial capacitance (dielectric layers at the electrode/solution interface) [ 25 ] at a single frequency was used as a parameter for detection of aβ in this report, the comparison of 2 sensing mechanism for non-Faradaic and Faradaic detection was shown in Figure 1 and Figure 2 . By removing the redox probe couple (Fe(CN) 6 ) 3−/4− in the measurement, we can avoid the binding of aβ peptide to metal ion Fe which is presented in the redox couple, forming the metal ion complexed aβ which is the cause of the denaturation of aβ peptide, giving disadvantage issues during the measurement [ 29 , 30 , 31 ]. Moreover, the experimental process become simpler and more suitable for point of care diagnosis without the application of redox probe.…”

Interactions of Whey Proteins with Metal Ions

“…In addition, Allen et al studied the effects of polarity on the structures and charge states of native-like proteins and complexes in the gas phase by ESI-MS and ion-mobility mass spectrometry [100]. Additionally, Lermyte et al studied metal ion binding to the β-amyloid monomer by native FT-ICR mass spectrometry [101] and effects of transition metals in proteinopathies by ESI-MS [98].…”