Multiple quantum solid-state NMR indicates a parallel, not antiparallel, organization of β-sheets in Alzheimer's β-amyloid fibrils

Abstract

Senile plaques associated with Alzheimer's disease contain deposits of fibrils formed by 39-to 43-residue ␤-amyloid peptides with possible neurotoxic effects. X-ray diffraction measurements on oriented fibril bundles have indicated an extended ␤-sheet structure for Alzheimer's ␤-amyloid fibrils and other amyloid fibrils, but the supramolecular organization of the ␤-sheets and other structural details are not well established because of the intrinsically noncrystalline, insoluble nature of amyloid fibrils. Here we report solid-state NMR measurements, using a multiple quantum (MQ) 13 C NMR technique, that probe the ␤-sheet organization in fibrils formed by the full-length, 40-residue ␤-amyloid peptide (A␤1-40). Although an antiparallel ␤-sheet organization often is assumed and is invoked in recent structural models for full-length ␤-amyloid fibrils, the MQNMR data indicate an in-register, parallel organization. This work provides site-specific, atomic-level structural constraints on full-length ␤-amyloid fibrils and applies MQNMR to a significant problem in structural biology.A variety of peptides and proteins form amyloid fibrils, including those involved in amyloid diseases such as Alzheimer's disease, type II diabetes, and spongiform encephalopathies (1, 2), as well as proteins that are studied primarily as models for the elucidation of fundamental aspects of protein biophysics (3, 4). Compared with monomeric or oligomeric forms of peptides and proteins, relatively little is known definitively about the molecular structure and supramolecular organization of amyloid fibrils. All amyloid fibrils exhibit similar morphologies in electron micrographs (Fig. 1A), despite their diversity of amino acid sequences and sequence lengths. X-ray diffraction measurements on oriented amyloid fibril bundles show a characteristic ''cross-␤'' pattern (2, 5-8), implying an extended ␤-sheet structure with polypeptide chains running roughly perpendicular to the long axis of the fibril and interchain hydrogen bonds roughly parallel to this axis. This ␤-sheet structure is supported by recent cryo-electron microscopy measurements (9). Finer structural details are generally not well established because amyloid fibrils are not amenable to structural characterization by single-crystal diffraction and highresolution, liquid-state NMR techniques.Amyloid fibrils that form senile plaques in Alzheimer's disease are comprised of ␤-amyloid (A␤) peptides that range in length from 39 to 43 residues (10-12). Various shorter fragments of the full-length A␤ peptides are also known to fibrillize in vitro (13)(14)(15)(16)(17)(18)(19)(20)(21). A number of structural models for full-length A␤ fibrils (8,(22)(23)(24)(25) and fibrils formed by A␤ fragments (13-16, 21) have been proposed, most (16,(21)(22)(23)(24)(25)(26), but not all (13-15), of which are based on an antiparallel ␤-sheet organization. Here we present solid-state 13 C NMR data, obtained with multiple quantum (MQ) NMR techniques based on time-reversal principles (27-32), which support an exte...

Spontaneous Fibril Formation by Polyalanines; Discontinuous Molecular Dynamics Simulations

“…The fibrils observed in our simulations mimic the structural characteristics observed in experiments in that most peptides within a β-sheet in our fibrils are highly parallel to one other [129][130][131] and moderately anti-parallel to peptides within neighboring β-sheets, the intrasheet (C α to C α ) distance is 5.05Å (±0.07) (compared to experimental values of 4.7-4.8Å 11,134,135 ), the inter-sheet (C α to C α ) distance is 7.5Å (±0.5) (compared to experimental values of 8-10Å 11,[134][135][136] ), and our fibrils contain about six β-sheets with each containing multiple peptides 11,[99][100][101] . Finally, we find that when the strength of the hydrophobic interaction between non-polar sidechains is high compared to the strength of the hydrogen bond interaction, amorphous rather than fibrillar aggregates are formed.…”

Solid-State Nuclear Magnetic Resonance Evidence for Parallel and Antiparallel Strand Arrangements in the Membrane-Associated HIV-1 Fusion Peptide

“…In amyloid, a single peptide sequence appears to form either a parallel or an antiparallel strand arrangement (65,(108)(109)(110).…”

Sensitivity enhancement in 13C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing 1H T1 relaxation

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Particularly, use of protein micro-/nano-crystals [17] has significantly improved resolution in high-resolution SSNMR of dilute spins such as 13 C and 15 N, permitting signal assignment and structural determination of various uniformly 13 C and/or 15 N-labeled proteins by SSNMR. [18][19][20][21][22][23][24][25] However, restricted sensitivity in 13 C and 15 N SSNMR has been still one of the major limiting factors in SSNMR analysis of proteins.…”