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  • 1
    ISSN: 1573-5001
    Keywords: CI2 ; chemical exchange ; constant-time ; hydration ; lysozyme ; NOE ; quadrature detection ; ROE ; water ; water flip-back
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A pulse sequence is proposed to select water magnetization with enhanced specificity through a synergetic combination of several filtering principles. This approach relies on a constant-time evolution period implemented without quadrature detection, which results in a √2 increase in signal-to-noise ratios as compared to traditional non-selective methods for water filtration. In addition, the quadrature-free constant-time block facilitates the implementation of the water flip-back strategy, which leads to further gains in sensitivity. The proposed experiment was applied to unlabeled HEW lysozyme and to 15 N-labeled chymotrypsin inhibitor 2 which was partially or non 13C-enriched. Water molecules belonging to a spine of hydration between two pseudo β-sheet strands were identified, solving previously reported discrepancies between the X-ray and the refined NMR structure of CI2. The proposed experiment is particularly suitable for hydration studies of mixtures of labeled and unlabeled components, such as ligand–macromolecule complexes.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 10 (1998), S. 28-34 
    ISSN: 0899-0042
    Keywords: collagen ; nuclear magnetic resonance (NMR) ; nuclear Overhauser effect (NOE) ; stereospecific assignment ; triple-helix ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An improved model-based method for the stereospecific assignment of prochiral centers in collagen-like triple-helical molecules is introduced. Using the concepts of reporter atoms and of ensemble NOEs, the proposed methodology extracts the stereochemical information contained in the chiral elements of triple-helices and transfers it to prochiral centers with nondegenerate proton resonances. The improved approach has been successfully validated using -(Gly-Pro-Hyp)n- triple-helices for which the stereospecific assignment was previously obtained with established techniques. We have applied our stereochemical characterization to novel peptoid containing triple-helices for which existing methods of stereospecific assignment can not be used for all the prochiral centers. In our approach, several different NOE measurements are employed to make a given stereospecific assignment. The multiple NOE comparisons allow internal cross checks, which reduce the chance of erroneous assignments caused by experimental artifacts including spin diffusion and bias from anisotropic rotational motions. In addition, the multiple NOE comparisons are useful in overcoming problems associated with resonance overlap often encountered in the 1H-NMR spectra of collagen-like molecules. Our stereochemical analysis is anticipated to improve the precision and accuracy of the characterization of collagen-like triple-helices through a better correlation of structures with their 1H-NMR spectra. Chirality 10:28-34, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-3904
    Keywords: SRIF ; Somatostatin ; Lanthionine ; Kaiser-oxime resin ; Peptide cyclization ; PCOR ; Solid-phase peptide synthesis ; Fmoc cleavage with DBU
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The synthesis of the lanthionine analog of somatostatin[1–14] on a Kaiser-oxime resin is described. The 12-residue peptide segment [3–14] was assembled and cyclized on the resin by using the method of peptide cyclization on an oxime resin (PCOR); the product was obtained with good yield (41%) and purity (94%). The Fmoc protecting group on the N-terminus was cleaved with DBU, followed by a 2+12 segment condensation in solution. The chromatographic (HPLC, CZE) and spectral (UV, NMR) properties of the lanthionine and the natural somatostatins have been studied and compared. Preliminary biological tests show that the lanthionine and the natural somatostatins exhibit similar binding affinities to somatostatin receptor SSTR2.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-5001
    Keywords: band-selective pulses ; chemical exchange-relay ; hydration ; lysozyme ; NOE ; water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A pulse sequence is proposed which uses a train of band-selective pulses for the editing of slow chemical exchange-relay effects in experiments designed to study water-macromolecule interactions. Compared to previous methods, this experiment does not require knowledge of the exact chemical shift of the relaying labile protons and needs only the recording of a single experiment to edit the relay through different exchanging groups resonating at different frequencies. The pulse sequence has been implemented using Gaussian cascades and was applied to the study of the hydration of HEW lysozyme.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A peptoid residue N-isobutylglycine (Nleu) was introduced as a proline surrogate in collagen-like triple helical structures. A series of single chain and template-assembled collagen-based peptide-peptoid structures composed of Gly-Pro-Nleu sequences were prepared by solid-phase segment condensation methods. Both a synthetic route in solution and a solid phase method were employed to couple the KTA (cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid, also known as the Kemp triacid) based template, KTA-(Gly-OH)3, to peptide-peptoid chains. Biophysical studies using CD, uv absorbance, and optical rotation measurements demonstrated that these compounds form triple-helical structures when the chains are longer than critical lengths. Results from melting curve measurements indicated that the Gly-Pro-Nleu sequence is comparable to the Gly-Pro-Pro sequence in stabilizing a triple-helical conformation. The KTA-based template stabilized triple-helical structures as can be seen by the increased melting temperatures as compared to equivalent single chain molecules. In addition, the template reduced the minimum chain length necessary to form a triple helix from six to only three trimer repeats. © 1996 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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