Hydrogen Exchange-Mass Spectrometry Analysis of β-Amyloid Peptide Structure

Abstract

beta-Amyloid peptide (A beta) is the primary protein component of senile plaques in Alzheimer's disease and is believed to be responsible for the neurodegeneration associated with the disease. A beta has proven to be toxic only when aggregated; however, the structure of the aggregated species associated with toxicity is unknown. In the present study, we use hydrogen-deuterium isotope exchange (HX)-electrospray ionization mass spectrometry (MS) along with enzymatic digestion as a tool to examine at near residue level, the changes in A beta structure associated with aggregation to a fibril form. Our results show that the structure of A beta intermediate species formed early in the course of fibrillogenesis is dependent upon solvent conditions. Additionally, the HX-MS data of peptic A beta fragments suggest that the C-terminal segment of the peptide is approximately 35% protected from exchange in fibril-containing samples, relative to monomeric A beta species prepared in DMSO/H(2)O. The N-terminus (residues 1-4) is completely unprotected from exchange, and the fragment containing residues 5-19 is over 50% protected from exchange in the fibril-containing samples. This work contributes to our understanding of A beta structure associated with aggregation and toxicity and further application of this approach may aid in the design of agents that intervene in the A beta aggregation processes associated with neurotoxicity.

Solid-support Electron Paramagnetic Resonance (EPR) Studies of Aβ40 Monomers Reveal a Structured State with Three Ordered Segments

“…For example, if multiple states give rise to different chemical shifts and the interconversion between different states is slow on NMR timescale, NMR is able to detect multiple structural states. Hydrogen exchange combined with mass spectrometry has also been shown to detect multiple structural states if different structural states have difference in their amide proton exchange rates (48). Other ensemble-based spectroscopic methods such as circular dichroism may not be able to resolve different structural states.…”

Experimental Constraints on Quaternary Structure in Alzheimer's β-Amyloid Fibrils

“…Experimental determination of secondary structure in amyloid fibrils therefore consists of the identification of structurally ordered and disordered segments, and the identification of β-strand and non-β-strand segments (i.e., loops, bends, or turns). Solid state nuclear magnetic resonance (NMR) (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19), hydrogen/deuterium (H/D) exchange (14,(20)(21)(22)(23)(24)(25)(26)(27), proline-scanning mutagenesis (28,29), electron paramagnetic resonance (EPR) (30)(31)(32), and infrared and Raman spectroscopies (33,34) have been applied to the problem of secondary structure determination. Tertiary structure in amyloid fibrils can be defined as the organization of β-strand segments into parallel or antiparallel β-sheets, with a specific registry of inter-strand hydrogen bonds within the β-sheets.…”

Molecular simulations of beta-amyloid protein near hydrated lipids (PECASE).

“…Research has been done on the structure and aggregation of Aβ experimentally (Lee et al, 1999;Mansfield et al, 1998;Mason et al, 1996;Pallitto et al, 1999;Terzi et al, 1997;Wang et al, 2003). Researchers pointed out that Aβ(17-21) fragment is critical in the aggregation of Aβ peptide (Mansfield et al, 1998;Pallitto et al, 1999).…”

“…Researchers pointed out that Aβ(17-21) fragment is critical in the aggregation of Aβ peptide (Mansfield et al, 1998;Pallitto et al, 1999). Good and coworkers reported important data on the fibril formation of Aβ (Lee et al, 2005;Wang et al, 2003). Hydrogen exchange-mass spectrometry(HX-MS) experiment revealing the distribution of species suggests that the N-terminus of the peptide does not participate in fibril formation, while the Cterminus is found to be important in fibril formation (Wang et al, 2003).…”

“…Good and coworkers reported important data on the fibril formation of Aβ (Lee et al, 2005;Wang et al, 2003). Hydrogen exchange-mass spectrometry(HX-MS) experiment revealing the distribution of species suggests that the N-terminus of the peptide does not participate in fibril formation, while the Cterminus is found to be important in fibril formation (Wang et al, 2003). Moreover, Hsp20, a novel α-crystalline protein, was found to drastically reduce Aβ toxicity to two different cells and the prevention of Aβ fibril formation was confirmed by electron microscopy in recent publication (Lee et al, 2005) .…”