M G Zagorski

Columbia University, New York City, NY, United States

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Publications (11)50.85 Total impact

  • M G Zagorski, C J Barrow
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    ABSTRACT: Beta-peptide is a major component of amyloid deposits in Alzheimer's disease. We report here a proton nuclear magnetic resonance (NMR) spectroscopic investigation of a synthetic peptide that is homologous to residues 1-28 of beta-peptide [abbreviated as beta-(1-28)]. The beta-(1-28) peptide produces insoluble beta-pleated sheet structures in vitro, similar to the beta-pleated sheet structures of beta-peptide in amyloid deposits in vivo. For peptide solutions in the millimolar range, in aqueous solution at pH 1-4 the beta-(1-28) peptide adopts a monomeric random coil structure, and at pH 4-7 the peptide rapidly precipitates from solution as an oligomeric beta-sheet structure, analogous to amyloid deposition in vivo. The NMR work shown here demonstrates that the beta-(1-28) peptide can adopt a monomeric alpha-helical conformation in aqueous trifluoroethanol solution at pH 1-4. Assignment of the complete proton NMR spectrum and the determination of the secondary structure were arrived at from interpretation of two-dimensional (2D) NMR data, primarily (1) nuclear Overhauser enhancement (NOE), (2) vicinal coupling constants between the amide (NH) and alpha H protons, and (3) temperature coefficients of the NH chemical shifts. The results show that at pH 1.0 and 10 degrees C the beta-(1-28) peptide adopts an alpha-helical structure that spans the entire primary sequence. With increasing temperature and pH, the alpha-helix unfolds to produce two alpha-helical segments from Ala2 to Asp7 and Tyr10 to Asn27. Further increases in temperature to 35 degrees C cause the Ala2-Asp7 section to become random coil, while the His13-Phe20 section stays alpha-helical. A mechanism involving unfavorable interactions between charged groups and the alpha-helix macrodipole is proposed for the alpha-helix----beta-sheet conversion observed at midrange pH.
    Biochemistry 07/1992; 31(24):5621-31. · 3.38 Impact Factor
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    ABSTRACT: The A4 or β-peptide (39 to 43 amino acid residues) is the principal proteinaceous component of amyloid deposits in Alzheimer's disease. Using circular dichroism (c.d.), we have studied the secondary structures and aggregational properties in solution of 4 synthetic amyloid β-peptides: β-(1–28), β-(1–39), β-(1–42) and β-(29–42). The natural components of cerebrovascular deposits and extracellular amyloid plaques are β-(1–39) and β-(1–42), while β-(1–28) and β-(29–42) are unnatural fragments.The β-(1–28), β-(1–39) and β-(1–42) peptides adopt mixtures of β-sheet, α-helix and random coil structures, with the relative proportions of each secondary structure being strongly dependent upon the solution conditions. In aqueous solution, β-sheet structure is favored for the β-(1–39) and β-(1–42) peptides, while in aqueous solution containing trifluoroethanol (TFE) or hexafluoroisopropanol (HFIP), α-helical structure is favored for all 3 peptides. The α-helical structure unfolds with increasing temperature and is favored at pH 1 to 4 and pH 7 to 10; the β-sheet conformation is temperature insensitive and is favored at pH 4 to 7. Peptide concentration studies showed that the β-sheet conformation is oligomeric (intermolecular), whereas the α-helical conformation is monomeric (intramolecular). The rate of aggregation to the oligomeric β-sheet structure (α-helix → random coil → β-sheet) is also dependent upon the solution conditions such as the pH and peptide concentration; maximum β-sheet formation occurs at pH 5.4. These results suggest that β-peptide is not an intrinsically insoluble peptide. Thus, solution abnormalities, together with localized high peptide concentrations, which may occur in Alzheimer's disease, may contribute to the formation of amyloid plaques.The hydrophobic β-(29–42) peptide adopts exclusively an intermolecular β-sheet conformation in aqueous solution despite changes in temperature or pH. Therefore, this segment may be the first region of the β-peptide to aggregate and may direct the folding of the complete β-peptide to produce the β-pleated sheet structure found in amyloid deposits. Differences between the solution conformations of the β-(1–39) and β-(1–42) peptides suggests that the last 3 C-terminal amino acids are crucial to amyloid deposition.
    Journal of Molecular Biology 07/1992; · 3.91 Impact Factor
  • R Orlando, P T Kenny, M G Zagorski
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    ABSTRACT: beta-peptide is a normal component of amyloid deposits in Alzheimer's disease. In aqueous solution, beta-peptide is extremely insoluble and rapidly aggregates forming oligomeric beta-sheet structures that eventually precipitate from solution. Presumably, this process is related to the production of amyloid deposits in Alzheimer's disease. Formic acid is commonly used to dissolve the beta-peptides and prevent aggregation in biological and biophysical studies. However, a side-reaction which covalently modifies beta-peptide is encountered with formic acid. In this report, fast atom bombardment mass spectrometry and tandem mass spectrometry demonstrate that both Ser8 and Ser26 become O-formylated in 70% aqueous formic acid solutions. The implications of this O-formylation upon the aggregational properties of beta-peptide are discussed.
    Biochemical and Biophysical Research Communications 05/1992; 184(2):686-91. · 2.41 Impact Factor
  • Michael G. Zagorski, Colin J. Barrow
    Biochemistry - BIOCHEMISTRY-USA. 01/1992; 31(24):5621-5631.
  • Ron Orlando, Peter T.M. Kenny, Michael G. Zagorski
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    ABSTRACT: β-peptide is a normal component of amyloid deposits in Alzheimer's disease. In aqueous solution, β-peptide is extremely insoluble and rapidly aggregates forming oligomeric β-sheet structures that eventually precipitate from solution. Presumably, this process is related to the production of amyloid deposits in Alzheimer's disease. Formic acid is commonly used to dissolve the β-peptides and prevent aggregation in biological and biophysical studies. However, a side-reaction which covalently modifies β-peptide is encountered with formic acid. In this report, fast atom bombardment mass spectrometry and tandem mass spectrometry demonstrate that both Ser8 and Ser26 become O-formylated in 70% aqueous formic acid solutions. The implications of this O-formylation upon the aggregational properties of β-peptide are discussed.
    Biochemical and Biophysical Research Communications. 01/1992;
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    ABSTRACT: Pardaxin is a mucosal secretion of the Pacific sole Pardachirus pavoninus that exhibits unusual shark repellent and surfactant properties [Thompson, S. A., Tachibana, K., Nakanishi, K., & Kubota, I. (1986) Science 233, 341-343]. This 33 amino acid polypeptide folds into ordered structures in trifluoroethanol-water solution and in micelles but adopts a random-coiled structure in water solution. The complete proton NMR spectrum of pardaxin P-2 has been assigned in CF3CD2OD/H2O (1:1) solution, and the three-dimensional structure has been elucidated with distance restrained molecular dynamics calculations. It is demonstrated that peptide segments within the 7-11 and 14-26 residue stretches are helical while residues at the C- and N-terminus exist predominantly in extended conformations in solution. The dipeptide 12-13 segment connecting the two helices exists as a bend or a hinge allowing the two helices to be oriented in a L-shaped configuration. These studies establish that pardaxin P-2 adopts a novel amphiphilic helix (7-11)-bend (12-13)-helix (14-26) motif with Pro-13 forming the focal point of the turn or bend between the two helices.
    Biochemistry 09/1991; 30(32):8009-17. · 3.38 Impact Factor
  • C J Barrow, M G Zagorski
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    ABSTRACT: The secondary structures in solution of the synthetic, naturally occurring, amyloid beta peptides, residues 1 to 42 [beta (1-42)] and beta (1-39), and related fragments, beta (1-28) and beta (29-42), have been studied by circular dichroism and two-dimensional nuclear magnetic resonance spectroscopy. In patients with Alzheimer's disease, extracellular amyloid plaque core is primarily composed of beta (1-42), whereas cerebrovascular amyloid contains the more soluble beta (1-39). In aqueous trifluoroethanol solution, the beta (1-28), beta (1-39), and beta (1-42) peptides adopt monomeric alpha-helical structures at both low and high pH, whereas at intermediate pH (4 to 7) an oligomeric beta structure (the probable structure in plaques) predominates. Thus, beta peptide is not by itself an insoluble protein (as originally thought), and localized or normal age-related alterations of pH may be necessary for the self-assembly and deposition of beta peptide. The hydrophobic carboxyl-terminal segment, beta(29-42), exists exclusively as an oligomeric beta sheet in solution, regardless of differences in solvent, pH, or temperature, suggesting that this segment directs the folding of the complete beta (1-42) peptide to produce the beta-pleated sheet found in amyloid plaques.
    Science 08/1991; 253(5016):179-82. · 31.03 Impact Factor
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    ABSTRACT: A structural study of trehalostatin 1, a specific inhibitor of blowfly trehalase, revealed that 1 contains an unusual five-membered pseudocyclitol.
    Journal of the Chemical Society Chemical Communications 01/1991;
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    ABSTRACT: Arc repressor is a 53-residue sequence-specific DNA binding protein. We report the assignment of the proton NMR spectrum and the secondary structure for the thermostable PL8 variant of Arc. This mutant, which differs from wild type by a Pro-8----Leu substitution, was chosen for study because its enhanced stability allows spectra to be acquired at elevated temperatures where spectral resolution is higher. The first five residues of the protein play important roles in DNA binding but appear to be disordered in solution. Residues 6-14 form the remaining part of the N-terminal DNA binding region of the protein and assume an antiparallel beta-conformation. This indicates that Arc is a member of a new class of DNA binding proteins. The observed interresidue nuclear Overhauser effects are consistent with a beta-strand, gamma-turn, beta-strand structure for the residue 6-14 region, although other structures are also consistent with the data. The remaining portion of the protein is predominantly alpha-helical. Residues 16-26 and 35-50 form amphipathic alpha-helices which may pack together in a four-helix bundle in the protein dimer.
    Biochemistry 01/1990; 28(25):9813-25. · 3.38 Impact Factor
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    ABSTRACT: High-resolution homonuclear and heteronuclear two-dimensional NMR studies have been carried out on the self-complementary d(C-C-G-C-G-A-A-T-T-C-C-G-G) duplex (designated GCG 13-mer) in aqueous solution. This sequence contains an extra cytidine located between residues G3 and G4 on each strand of the duplex. The exchangeable and nonexchangeable proton resonances have been assigned from an analysis of two-dimensional nuclear Overhauser enhancement (NOESY) and correlated (COSY and relay COSY) spectra for the GCG 13-mer duplex in H2O and D2O solution. The extra cytidine at the bulge site (designated CX) results in more pronounced changes in the NOE distance connectivities for the G3-CX-G4 segment centered about the CX residue compared to the C9-C10 segment on the partner strand opposite the CX residue for the GCG 13-mer duplex at 25 degrees C. The cross-peak intensities in the short mixing time NOESY spectrum also establish that all glycosidic torsion angles including that of CX are anti in the GCG 13-mer duplex at 25 degrees C. The observed chemical shift changes for the CX base protons and the G3pCX phosphorus resonance with temperature between 0 and 40 degrees C demonstrate a temperature-dependent conformational equilibrium in the premelting transition region. The NOE and chemical shift parameters establish that the predominant conformation at low temperature (0 degree C) has the extra cytidine looped out of the helix with the flanking G3.C10 and G4.C9 base pairs stacked on each other. These results support conclusions based on earlier one-dimensional NMR studies of extra cytidine containing complementary duplexes in aqueous solution [Morden, K. M., Chu, Y. G., Martin, F. H., & Tinoco, I., Jr. (1983) Biochemistry 22, 5557-5563. Woodson, S. A., & Crothers, D. M. (1987) Biochemistry 26, 904-912]. By contrast, the chemical shift and NOE parameters demonstrate that the conformational equilibrium shifts toward a structure with a stacked extra cytidine on raising the temperature to 40 degrees C prior to the helix-coil melting transition. The most downfield shifted phosphorus resonance in the GCG 13-mer duplex has been assigned to the phosphate in the C2-G3 step, and this observation demonstrates that the perturbation in the phosphodiester backbone extends to regions removed from the (G3-CX-G4).(C9-C10) bulge site.
    Biochemistry 01/1989; 28(1):294-303. · 3.38 Impact Factor
  • Michael G Zagorski, David G Norman
    Journal of Magnetic Resonance (1969) 01/1989; 83(1):167-172.