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  • Chemistry  (10)
  • 1990-1994  (7)
  • 1985-1989  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Cooperativity of carbohydrate moiety orientation and β- turn stability is determined by intramolecular hydrogen bonds in protected glycopeptide modelsThis is publication No. 1708 from the Graduate Department of Biochemistry, Brandeis University, Waltham, Massachusetts, 02254-9110 (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 1549-1564 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 2, 3, 4, 6-Tetra-O-acetyl-β-D-gluco-, and β-D-galactopyranosides, as well as approximately 4 : 1 anomeric mixtures of α- and β-mannopyranosides of Boc-X-Y-NHCH3 dipeptides (X-Y = Pro-Ser, Pro-D-Ser, Val-Ser, Val-D-Ser, and Gly-Ser) have been synthesized. CD and ir spectroscopic studies were performed to characterize the conformation of the glycosylated peptide backbone and examine the possible formation of intrapeptide and glycopeptide intramolecular H-bonds. It was found that O-glycosylated peptides containing a D-serine residue are likely to adopt a type II β-turn while those with the Pro-Ser or Val-Ser sequence feature a type I(III) β-turn in solution. Glycosylation also increases the magnitude of the CD bands, characteristic of the given type of β-turns, which can be interpreted as an indication of the stablization of the folded backbone conformation. Infrared data showed that in nonpolar solutions the peracetyl glycopeptides adopt both single- and double H-bonded conformations whose ratio, in some cases, depends on the position at C-2′ of the H-bond acceptor acetoxy group. These data suggest that five-, seven-, or ten-membered glyco-turns may play an important role in fixing the steric orientation of the carbohydrate antennae systems in glycoproteins.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360291206
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  • 2
    Electronic Resource
    Electronic Resource
    Environment-dependent conformation of Boc-Pro-Ser-NHCH3 (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 763-771 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of Boc-Pro-Ser-NHCH3 (1) was studied in the solid state and in solution. In the crystal, the steric structure of 1 is characterized by an E(cis) urethane tertiary amide bond and the lack of intramolecular H bonds. Four-hundred megahertz 1H- and 101-MHz 13C-nmr studies in CDCl3 clearly show the presence of two conformers differing in the rotameric state of the tertiary-amide bond. Selective 1H-13C nuclear Overhauser enhancement experiments at -20°C as well as 1H-nmr and ir data indicate that the major trans conformer (84% in CDC13) may adopt a type I β-turn conformation with a possible Oγ - H-N interaction, similarly to Piv-Pro-Ser HCH3 (2) [A. Aubry, N. Ghermani, and M. Mar-raud (1984) Int. J. Peptide Protein Res. 23, 113-122]. Molecular mechanics calculations on the cis rotamer show that the β-pleated-like backbone conformation of serine in the crystal of 1 is not a low-energy state for the isolated molecule; it is caused by packing forces, particularly by the helical network of intermolecular H bonds.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360300711
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  • 3
    Electronic Resource
    Electronic Resource
    Chiroptical labeling of folded polypeptide conformations: The thioamide probe (1990)
    New York : Wiley-Blackwell
    Biopolymers 30 (1990), S. 1061-1072 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This paper reports the chiroptical properties of thionated N-acyl amino acid and N-acyl dipeptide N′-methylamide models. It was found that the optical activity of the thioamide chromophore is dominated by the chiral contribution of perturbants attached to Cα at the N-H side of the thioamide group. The appearance of a strong negative ππ* band near 270 nm is indicative of the semiextended conformation of this residue. The φ ∼ -70°, ψ ≥ 120° set of torsion angles is compatible with a type II βt-turn or a γt-turn conformation with the perturbing N-H side residue in the i + 1 position of the turn. (The subscript t or tt denotes that one or both of the H-bonded moieties is thioamide.) Earlier data show that both βt- and γt-turns may be fixed by C=S⃛H-N(CO) intramolecular H bonds. The appearance of one or two weak nπ* bands and a positive ππ* band at about 270 nm is characteristic of type II βt-turns containing the H-bonded thioamide group attached to the glycine residue in position i + 2. The extended conformation (φ ∼ -140°, ψ ∼ 140°) of a residue after the thioamide group gives rise to a negative nπ* and a positive ππ* band of comparable magnitude. Peptid1e sequences with alternating thioamide-amide-thioamide backbone tend to adopt 1t ⇆ 4t H-bonded βtt conformations. CD studies show that type II βtt-turns have unique chiroptical properties: the ππ* region is dominated by an exceedingly strong negative band near 260 nm (|Δε| = 19-24) accompanied by a weaker band at higher wavelength values.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360301107
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  • 4
    Electronic Resource
    Electronic Resource
    β-Turns in bridged proline-containing cyclic peptide models (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 1555-1572 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis, CD, ir spectroscopic, and conformational studies of a series of bridged cyclic peptides of the general formula, cyclo[NH-(CH2)n-CO-Gly-Pro-Y-Gly] (2a-d, Y = Gly or Ser(OBut), n = 4 or 2) is reported. As indicated by difference nuclear Overhauser enhancement and Fourier transform ir experiments, the tetrapeptide sequence of cyclo[NH-(CH2)4-CO-Gly-Pro-Gly-Gly] (2a) and cyclo[NH-(CH2)2-CO-Gly-Pro-Gly-Gly] (2b) adopts a 1 ← 4 hydrogenbonded type II β-turn conformation in solution, while cyclo[NH-(CH2)4-CO-Gly-Pro-Ser(OBut) -Gly] (2c) features a type I β-turn, fixed by 1 ← 4 and Oγ … NH intramolecular H bonds. In aqueous solution 2a and 2c show class B and class C CD spectra, respectively. This is the first case reported of a typical class C CD pattern in aqueous solution for a conformationally mobile system having a type I β-turn. Based on the comparison of the band intensities of the bridged models with those of linear and cyclic model systems reported earlier, a set of subspectra with reduced band intensities is suggested for use in the CD analysis of the conformation of polypeptides in solution.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360260908
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  • 5
    Electronic Resource
    Electronic Resource
    CD and Fourier transform ir spectroscopic studies of peptides. II. Detection of β-turns in linear peptides (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 177-185 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Comparative CD and Fourier transform ir (FTIR) spectroscopic data on N-Boc protected linear peptides with or without the (Pro-Gly) β-turn motif (e.g., Boc-Tyr-Pro-Gly-Phe-Leu-OH and Boc-Tyr-Gly-Pro-Phe-Leu-OH) are reported herein. The CD spectra, reflecting both backbone and aromatic contributions, were not found to be characteristic of the presence of β-turns. In the amide I region of the FTIR spectra, analyzed by self-deconvolution and curve-fitting methods, the β-turn band shewed up between 1639 and 1633 cm-1 in trifluoroethanol (TFE) but only for models containing the (Pro-Gly) core. This band war-also present in the spectra in chloroform but absent in dimethylsulfoxide. These findings, in agreement with recent ir data on cyclic models and 310-helical polypeptides and protein in D2O [see S. J. Prestrelski, D. M. Byler, and M. P. Thompson (1991), International Journal of Peptide and Protein Research, Vol. 37, pp. 508-512; H. H. Mantsch, A. Perczel. M. Hollósi, and G. D. Fasman (1992), FASEB Journal, Vol. 6, p. A341; H. H. Mantsch. A. Perczel, M. Hollósi, and G. Fasman (1992), Biopolymers. Vol. 33, pp. 201-207; S. M. Miick, G. V. Martinez, W. R. Fiori, A. P. Tedd, and G. L. Millhauser (1992). Nature, Vol. 359, pp. 653-655], suggest that the amide I band, with a major contribution from the acceptor C = O of the 1 ← 4 intramolecular H bond of β-turns, appears near or below 1640 cm-1, rather than above 1660 cm-1. In TFE, bands between 1670 and 1660 cm-1 are mainly due to “free” carbonyls, that is, C = O's of amides that are solvated but not involved in the characteristic H bonds of periodic secondary structures or β-turns. © 1994 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340204
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  • 6
    Electronic Resource
    Electronic Resource
    Ca2+-induced conformational transitions of phosphorylated peptides (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 497-510 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CD spectroscopic studies on protected peptides containing lysine and serine, or phosphoserine, and on serine-containing fragments of the neurofilament protein midsized subunit, both in the unphosphorylated and phosphorylated form, are reported. The introduction of the phosphoryl group was not found to have a significant spectral effect in aqueous solution. In trifluoroethanol (TFE), spectral shifts toward unordered (type U) spectra or the appearance of distorted spectra likely reflect the adoption of aperiodic polypeptide conformations due to salt bridge(s) between negatively charged phosphoserine and positive lysine side-chain groups. A turn-stabilizing effect of phosphorylation was also observed.CD-monitored titration experiments in TFE revealed a high conformational sensitivity of phosphopeptides toward Ca2+ ions. The appearance of the unordered spectra or spectral shifts were the sign of a bulk disordering effect of Ca2+ ions. Spectra with specific spectroscopic features reflect the formation of Ca2+complexes and the adoption of ordered unique backbone conformations.When ordered structures were obtained on addition of Ca2+ ions, the observed CD curves showed a resemblance to the spectrum of β-pleated sheets. This may originate from chain extension and the formation of β-pleated sheet segments fixed by Ca2+ bridges between PO3H1- groups of adjacent peptide chains. The data clearly show that the effect of the Ca2+ ions is highly specific: the sequence, chain length, presence and distribution of charged side-chain groups, degree and site of phosphorylation, and environmental factors appear to be determining in the process of chain extension or β-sheet formation. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330316
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  • 7
    Electronic Resource
    Electronic Resource
    Melting of the left-handed helical conformation of charged poly-L-lysine (1994)
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 1123-1124 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360340816
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  • 8
    Electronic Resource
    Electronic Resource
    Studies on proline-containing tetrapeptide models of β-turnsDedicated to Elkan R. Blout on the occassion of his sixty-fifth birthday. (1985)
    New York : Wiley-Blackwell
    Biopolymers 24 (1985), S. 211-242 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a series of protected tetrapeptides of the general formula Cbz-Gly-X2-Y3-Gly-OR (R = stearyl or methyl, X and/or Y = proline) is described. Detailed CD studies have been performed to evaluate the contribution of proline-containing β-turns to the CD spectra of proteins. The CD spectra of all the models are dominated by the chiral contribution of the proline residue. In polar, proton-donating solvents, a poly-proline II-like spectrum was observed in almost all cases. The tetrapeptide model Cbz-Gly-Gly-Pro-Gly-OStearyl, in acetonitrile shows a type C spectrum that has not been previously reported for linear peptides. The ir and nmr data on this model support the assumption of that of a type III β-turn, exhibiting a type C spectrum, participate in the conformational equilibrium. The most interesting finding of the CD studies is the observation of a type D spectrum (according to the classification of Woody [Woody, R. W. (1974) in Peptides, Polypeptides and Proteins, Blout, E. R. Bovey, F. A. Lotan, N. & Goodman, M. (Eds.), Wiley, New York]) for models Cbz-Gly-Pro-Asp(OBut)-Gly-OStearyl and Cbz-Gly-Pro-Ser(OBut)-Gly-OStearyl in cyclohexane. The results of the CD measurements ae discussed in correlation with ir and nmr data and with recent literature.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360240117
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  • 9
    Electronic Resource
    Electronic Resource
    β-Turns in serine-containing linear and cyclic models (1987)
    New York : Wiley-Blackwell
    Biopolymers 26 (1987), S. 1527-1553 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Tetrapeptides, Cbz-Gly-X-Y-Gly-OSt (1-4) - as well as cyclic systems, cyclo[NH-(CH2)n-CO-Gly-Ser(OX)-Ser(OX)-Gly] (5 and 6; n = 4 and 2, X = But or H), have been synthesized in order to compare the CD spectrum of linear and cyclic β-turn models containing either a protected or a free hydroxyl of the serine residue. In extremely dilute cyclohexane solution the linear models Cbz-Gly-Ser-Y-Gly-OSt (1-3a) show class B spectra with very strong positive bands, contrary to other members of the series. Based on 200-MHz 1H nuclear overhauser enhancement and Fourier transform ir studies, Cbz-Gly-Ser-Ser(OBut)-Gly-OSt (3a) in dilute chloroform solution assumes a distorted type II β-turn conformation fixed by an extended system of intramolecular H bonds. As evidenced by 1H-nmr and FT-IR experiments, the cyclic model cyclo[NH-(CH2)4-CO-Gly-Ser(OBut)- Ser(OBut)-Gly] (5a) in a 1 : 1 mixture of (CD3)2SO-CDCl3 is also characterized by a type II β-turn encompassing the Ser3(OBut)-Gly4 sequence. In water, a class B pattern was measured for this model, in good agreement with theoretical and experimental studies that show that type II β-turns are generally characterized by class B spectra. In the protected and free OH cyclic models, cyclo[NH-(CH2)2-CO-Gly-Ser(OX)-Ser(OX)-Gly] (5b and 6b, X = But or H) distortions of the peptide backbone due to the loss of two CH2 groups result in the appearance of CD spectra characterized by a strong negative band near 200 nm, interpreted as a sign of the lack of β-turn structures in these models. This observation, together with other CD data discussed in this paper, clearly show that the CD of serine-containing β-turn sequences strongly depends on long-range backbone and local side-chain interactions.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360260907
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  • 10
    Electronic Resource
    Electronic Resource
    Characterization of β-turns in cyclic hexapeptides in solution by fourier transform IR spectroscopy (1993)
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 201-207 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The β-turn represents a structural element frequently encountered in globular proteins. However, in spite of various theoretical and experimental studies the ir signature bands of pure β-turns are still not established beyond doubt. Although considerable information exists now on the ir spectra of β-helical and β-sheet structures, the lack of knowledge concerning turn structures in general, and that of β-turns in particular, presents a major uncertainty in the estimation of global protein secondary structures from ir spectroscopic data. To obtain more specific information about the characteristic amide bands in β-turns, we report herein an ir spectroscopic analysis of a series of five cyclic pseudo-hexapeptides known to form β-turns from previous CD and nmr studies [A. Perczel, M. Hollósi, B. M. Foxman, and G. D. Fasman (1991) Journal of the American Chemical Society, Volume 113, pp. 9772-9784 ]. We show here that in these cyclic peptides the amide groups involved in β-turns that comprise a ten-membered hydrogen-bonded ring (and represent the first H-bond pair in a β-sheet), give rise to characteristic amide I bands in the range 1638-1646 cm-1, with the exact position depending on the solvent and the nature of the side-chain substituents. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360330202
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