Amyloid Fibril Formation by Aβ<sub>16-22</sub>, a Seven-Residue Fragment of the Alzheimer's β-Amyloid Peptide, and Structural Characterization by Solid State NMR

The HIV-1 fusion peptide serves as a useful model system for understanding viral/target cell fusion, at least to the lipid-mixing stage. Previous solid-state NMR studies have shown that the membranebound HIV-1 fusion peptide adopts an extended conformation in a lipid mixture close to that of host cells of the virus. In the present study, solid-state NMR REDOR methods were applied for detection of oligomeric strand structure. The samples were prepared under fusogenic conditions and contained equimolar amounts of two peptides, one with selective [ 13 C]carbonyl labeling and the other with selective [ 15 N]amide labeling. In the REDOR measurements, observation of reduced 13 C intensity due to hydrogen-bonded amide 15 N provides strong experimental evidence of oligomer formation by the membrane-associated peptide.Comparison of REDOR spectra on samples that were labeled at different residue positions suggests that there are both parallel and antiparallel arrangements of peptide strands. In the parallel arrangement, interpeptide hydrogen bonding decreases toward the C-terminus, while in the antiparallel arrangement, hydrogen bonds are observed along the entire length of residues which was probed (Gly-5 to Gly-16). For the parallel arrangement, these observations are consistent with the model in which the apolar N-terminal and central regions of the peptides penetrate into the membrane and hydrogen bond with one another while the polar C-terminus of the peptide is outside the membrane and hydrogen bonds with water. These measurements show that, at least at the end state of fusion, the peptide can adopt an oligomeric strand structure.Fusion between the membranes of enveloped viruses such as HIV-1 1 and influenza and the membranes of their target host cells is an essential step in infection (1-4). For these viruses, this process is mediated by integral membrane viral envelope proteins which contain N-terminal ∼20-residue apolar fusion peptide domains. For HIV-1 and influenza, the free fusion peptide has also been shown to be a useful model to understand fusion, at least to the lipid-mixing stage. The free peptide causes fusion of liposomes and erythrocytes, and numerous mutational studies have shown strong correlations between fusion peptide-induced liposome fusion and viral/host cell fusion (5-20). Recent studies suggest that envelope protein regions other than the fusion peptide also interact with membranes and play a role in fusion (21-26).There is a crystal structure of the part of the influenza hemagglutinin envelope protein which lies outside the virus and which contains the fusion peptide (27). This "ectodomain" structure corresponds to a prefusogenic conformation. For both the hemagglutinin and the HIV-1 gp41 envelope proteins, there are also atomic resolution structures of the "soluble ectodomains" which do not contain the fusion peptide (28-34). These structures are believed to correspond to the protein conformations after fusion has occurred and perhaps during fusion as well. In each of these soluble...

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

Section: Discussionmentioning

confidence: 99%

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

Yang

Weliky

2003

Biochemistry

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“…The majority of residues exhibit secondary shifts consistent with β-strand conformations, i.e., positive secondary shifts for C β sites and negative secondary shifts for CO and C α sites (16,80). Deviations from this pattern are observed at His18 (for C α ), Ser20 (for CO), Asn21 (for C α and Cβ), Leu27 (for C α and C β ), Ser28 (for C α ), and Asn31 (for C α ).…”

Section: Characterization Of Secondary Structure By 13 C Nmrmentioning

confidence: 99%

“…In light of current knowledge that the ability to form amyloid fibrils is not an unusual property for a peptide (10), the fact that short peptides representing residues 20-29 form fibrils (56,89) does not imply that this segment constitutes the core of full-length amylin fibrils. In fact, the molecular structures of fibrils formed by short peptides can be qualitatively different from the structures of the corresponding segments in the context of full-length peptide fibrils, as demonstrated by findings that certain β-amyloid fragments form antiparallel β-sheets in amyloid fibrils (16,19,24,78), while other fragments (15,26,27) and full-length β-amyloid (15,17,21) form parallel β-sheets. Evidence from Griffiths et al for antiparallel β-sheets in fibrils formed by residues 20-29 of human amylin (25) indicates that, as in the case of β-amyloid fibrils, the molecular structures in fibrils formed by amylin fragments need not reflect the molecular structure of full-length amylin fibrils.…”

mentioning

confidence: 99%

“…From the standpoint of molecular structure, the defining feature of an amyloid fibril is the presence of cross-β supramolecular structure, meaning that the β-sheets within the fibril are formed by β-strand segments that run approximately perpendicular to the long axis of the fibril and are linked by hydrogen bonds that run approximately parallel to this axis (11)(12)(13). Although determination of the molecular structures of amyloid fibrils is made difficult by their inherent noncrystallinity and insolubility, techniques such as solid state nuclear magnetic resonance (NMR) (12,(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33), electron paramagnetic resonance (EPR) (34)(35)(36), electron microscopy (37)(38)(39)(40)(41)(42)(43), hydrogen/deuterium exchange (29,(44)(45)(46)(47), scanning mutagenesis (48), chemical crosslinking (27,49,50), and x-ray diffraction of amyloid-like crystals …”

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confidence: 99%

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Peptide Conformation and Supramolecular Organization in Amylin Fibrils: Constraints from Solid-State NMR

et al. 2007

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The 37-residue amylin peptide, also known as islet amyloid polypeptide, forms fibrils that are the main peptide or protein component of amyloid that develops in the pancreas of type 2 diabetes patients. Amylin also readily forms amyloid fibrils in vitro that are highly polymorphic under typical experimental conditions. We describe a protocol for the preparation of synthetic amylin fibrils that exhibit a single predominant morphology, which we call a striated ribbon, in electron microscope and atomic force microscope images. Solid state nuclear magnetic resonance (NMR) measurements on a series of isotopically labeled samples indicate a single molecular structure within the striated ribbons. We use scanning transmission electron microscopy and several types of one-dimensional and two-dimensional solid state NMR techniques to obtain constraints on the peptide conformation and supramolecular structure in these amylin fibrils, and derive molecular structural models that are consistent with the experimental data. The basic structural unit in amylin striated ribbons, which we call the protofilament, contains four-layers of parallel β-sheets, formed by two symmetric layers of amylin molecules. The molecular structure of amylin protofilaments in striated ribbons closely resembles the protofilament in amyloid fibrils with similar morphology formed by the 40-residue β-amyloid peptide that is associated with Alzheimer's disease. Keywordsislet amyloid polypeptide; type 2 diabetes; amyloid fibril structure; electron microscopy; atomic force microscopy Amylin, also called islet amyloid polypeptide or IAPP, is a 37-residue peptide that is cosecreted with insulin by the β-cells of pancreas. The normal biological effects of amylin secretion include inhibition of glucagon secretion and reduction of the rate of gastric emptying, effects that contribute to the maintenance of postprandial glucose homeostasis (1). Amylin is the major peptide or protein component of the islet amyloid found in the pancreas of approximately 90% of type 2 (or non-insulin-dependent) diabetes patients (2,3). Fibrillar amylin has been shown * Corresponding author: Dr. Robert Tycko, National Institutes of Health, Building 5, Room 112, Bethesda, MD 20892-0520. phone 301-402-8272. fax 301-496-0825. e-mail robertty@mail.nih.gov.Supporting Information Available HPLC chromatograms from the purification of both reduced and oxidized amylin by reverse-phase chromatography ( Figure S1); FPLC chromatograms from the purification of both human and rodent amylin by size-exclusion chromatography ( Figure S2); 1D 13 C spectra of amylin fibrils with various isotopic labeling patterns, in lyophilized and rehydrated conditions ( Figures S3-S5); Table of 13 C NMR chemical shifts in amylin fibrils, TALOS predictions of backbone torsion angles based on these shifts, and torsion angles determined from 15 N fpRFDR-CT measurements (Table S1). This material is freely available on the World Wide Web at http://www.acs.org. to be toxic to cultured β-cells (4), and has been propo...

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“…While the structure of amyloid fibrils is not known in atomic detail, it is well established that the core of the typical amyloid fibril is composed of β-sheets whose strands run perpendicular to the fibril axis [41]. For Aβ 16−22 fibrils, there is evidence from solid-state NMR that the β-strands have an antiparallel organisation [42,43]. Figure 6 shows our results for the α-helix and β-strand contents H and S against temperature for the different numbers of chains, N c .…”

Section: Aggregationmentioning

confidence: 99%

Peptide folding and aggregation studied using a simplified atomic model

Irbäck¹

2005

J. Phys.: Condens. Matter

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Abstract:Using an atomic model with a simplified sequence-based potential, the folding properties of several different peptides are studied. Both α-helical (Trp cage, F s ) and β-sheet (GB1p, GB1m2, GB1m3, Betanova, LLM) peptides are considered. The model is able to fold these different peptides for one and the same choice of parameters, and the melting behaviour of the peptides (folded population against temperature) is in very good agreement with experimental data. Furthermore, using the same model with unchanged parameters, the aggregation behaviour of a fibril-forming fragment of the Alzheimer's Aβ peptide is studied, with very promising results.

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Amyloid Fibril Formation by Aβ_16-22, a Seven-Residue Fragment of the Alzheimer's β-Amyloid Peptide, and Structural Characterization by Solid State NMR

Cited by 702 publications

References 78 publications

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

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

Peptide Conformation and Supramolecular Organization in Amylin Fibrils: Constraints from Solid-State NMR

Peptide folding and aggregation studied using a simplified atomic model

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Amyloid Fibril Formation by Aβ16-22, a Seven-Residue Fragment of the Alzheimer's β-Amyloid Peptide, and Structural Characterization by Solid State NMR

Cited by 702 publications

References 78 publications

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

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

Peptide Conformation and Supramolecular Organization in Amylin Fibrils: Constraints from Solid-State NMR

Peptide folding and aggregation studied using a simplified atomic model

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Amyloid Fibril Formation by Aβ_16-22, a Seven-Residue Fragment of the Alzheimer's β-Amyloid Peptide, and Structural Characterization by Solid State NMR