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  • 1
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report the solid-phase synthesis and conformational analysis of a 14-membered, cyclic enkephalin analog, H—Tyr—c[—D—A2bu—Gly—Phe—D—Leu—] (where A2bu represents α,γ-diaminobutyric acid). The results from the guinea pig ileum (GPI) and mouse vas deferens (MVD) assays show that the analog, though active, has little selectivity for the μ or δ opioid receptors. Conformational analysis is carried out using 1H-nmr and computer simulations, including molecular dynamics and energy minimizations. The results obtained here are compared with the findings of our studies carried out on the μ-receptor-selective diastereomer, H—Tyr—c[—D—A2bu—Gly—Phe—Leu—] [N. Mammi, M. Hassan, and M. Goodman (1985) J. Am. Chem. Soc. 107, 4008-4013]. This comparison allows for insight into the regiospecificity of these cyclic enkephalin analogs.
    Additional Material: 3 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 1277-1282 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A penalty function for scalar coupling constants has been applied in molecular dynamics simulations as an experimental constraint. The function is based on the difference between the coupling constant calculated from the dihedral angle and the experimentally measured coupling constant. The method is illustrated on a model cyclic pentapeptide for which 3JHN-Hα and 3JHN-Cβ, both about the φ backbone dihedral angle, have been measured. The function is efficient in producing structures consistent with the scalar couplings, but removed from the conformation observed in solution. This arises from the lack of J restraints for the ψ dihedral angle. Simulation with both nuclear Overhauser effect (NOE) and J-coupling restraints illustrates small but significant differences from simulations using only NOEs. © 1992 John Wiley & Sons, Inc.
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  • 3
    ISSN: 0006-3525
    Keywords: parathyroid hormone ; parathyroid hormone-related protein ; G-protein coupled receptors ; peptide conformations in micelles ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The third-cytoplasmic loop of the G-protein coupled receptor responsible for the activity of parathyroid hormone and parathyroid hormone-related protein has been structurally characterized in aqueous solution in the presence of sodium dodecylsulfate and dodecylphosphocholine micelles. The high-resolution conformation of the 29-amino acid peptide containing the sequence of the cytoplasmic loop was obtained by CD and nmr. The structure was refined using a two-step distance geometry based method that first includes the removal of all side chains to quickly locate the globular fold of the peptide. After a simulated annealing protocol, the side chains are added in a random fashion. The resulting conformation was further refined with nuclear Overhauser enhancement restrained molecular dynamics using a two-phase simulation cell consisting of carbon tetrachloride and water as a mimetic of the biphasic, hydrophobic/hydrophilic character of the micelles in which the experimental measurements were carried out. The topological orientation of the cycloplasmic loop within the micelle was determined by addition of 5-doxylstearate and monitoring the decrease of nmr signal intensities from the radical-induced relaxation. The conformation and relative orientation of the peptide provided insight into the mechanism by which the cytoplasmic portion of the receptor activates the heterotrimeric, guanine nucleotide-binding regulatory protein, one of the first steps in signal transduction. © 1997 John Wiley & Sons, Inc. Biopoly 40: 653-666, 1996
    Additional Material: 12 Ill.
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  • 4
    ISSN: 0006-3525
    Keywords: antibiotic, conformation of antibiotic ; nmr structure refinement ; cation transport ; micelles ; structure in micelles ; spectroscopy in micelles ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and dynamics of the ionophoric antibiotic monensin in the presence of micelles have been determined. The conformation of monensin was derived from 50 nuclear Overhauser enhancement (NOE) derived distance restraints and metric-matrix based distance geometry calculations. The conformation was further refined with extensive NOE restrained molecular dynamics simulations carried out in a biphasic simulation cell. From the addition of doxylstearate and monitoring of the induced relaxation of the nmr signals, the relative topological orientation of the molecule within the micelle was ascertained. The results indicate two dihedral angles that act as hinge regions allowing the molecule to adopt a wide range of conformations. Considering the biological activity of monensin, i.e., the capture and transport of cations across cell membranes, an open and closed form of monensin have been postulated. The identification of these hinge regions, which are only observed in the membrane-like environment of the detergent micelles, provides insight into the mechanism of action and can serve as targets for modification to alter the biological profile of monensin. © 1997 John Wiley & Sons, Inc. Biopoly 42: 759-769, 1997
    Additional Material: 8 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 627-632 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 179-196 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To examine the importance of the aromatic side chains of enkephalin on opiate activity, we report the synthesis and conformational analysis of a series of analogues related to enkephalin with β-naphthylalanine in place of phenylalanine at the fourth position. Three linear analogues (Tyr-D-Ala-Gly-(L and D)-β Nal(1)-Leu-NH2 and Tyr-D-Ala-Gly-β Nal(2)-Leu-NH2) were initially synthesized to examine the effect of the substitution on biological activity. The increased activity of these peptides at the μ-opiate receptor, compared to native Leu-enkephalin, prompted us to examine the more conformational constrained analogues, Tr-c[D-A2bu-Gly-(L and D)-β Nal(1)-Leu], incorporating a α,γ-diaminobutyric acid at the second position and cyclization to the carboxylic end of the leucine. These two cyclic analogues provide insight into the necessity for the L chirality of the aromatic residue at position 4. The Tyr-c[D-A2bu-Gly-L-β Nal(1)-Leu] analogue is highly potent and displays a slight preference for the μ receptor. The conformational analysis indicates that despite the high flexibility of the tyrosine side chain, the aromatic rings of the tyrosine and naphthylalanine are relatively distant from each other. The presence of two intramolecular hydrogen bonds help maintain the conformation of the 14-membered backbone ring that keeps the side chains directed away from each other. These findings are in agreement with our model of an extended structure required for μ selectivity and a folded form with close aromatic ring placement for δ selectivity.
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  • 7
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In a continuation of our program to study the structure-activity relationship of peptide opiates, we report the conformational analysis of two cyclic tetrapeptides related to dermorphin - Tyr-c[D-Orn-Phe-Asp]-NH2 and Tyr-c[D-Asp-Phe-Orn]-NH2. These analogues have similar binding properties marked by a high selectivity for the μ-opioid receptors because of a drastic decrease in the affinity for the δ-opioid receptor. The conformational preferences of these analogues of dermorphin determined from proton nmr, molecular dynamics, and energy minimizations are quite similar. The constraint of the 13-membered ring formed from cyclization is quite evident from the conformational analysis. The constrained ring system acts as a template maintaining the relative orientation of the exocyclic tyrosine and side chain of phenylalanine. Two intramolecular hydrogen bonds measured for the D-Orn analogue in DMSO were disrupted upon the addition of water. For the D-Asp analogue, two intramolecular hydrogen bonds were found stable in DMSO and water. The global conformations of the two peptides determined from nuclear Overhauser effects did not change with the solvent titration. The difference in the hydrogen bonding within the 13-membered ring may account for the slight differences observed in the efficacy of the analogues at the μ-opioid receptors.
    Additional Material: 10 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 33 (1993), S. 1003-1017 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this article a few methods or modifications proven to be useful in the conformational examination of peptides and related molecules by molecular dynamics are illustrated. The first is the explicit use of organic solvents in the simulations. For many cases such solvents are appropriate since the nmr measurements (or other experimental observations) were carried out in the same solvent. Here, the use of dimethylsulfoxide and chloroform in molecular dynamics is described, with some advantages of the use of these solvents highlighted.A constant allowing for the scaling of the nonbonded interactions of the force field, an idea previously employed in distance geometry and simulated annealing, has been implemented. The usefulness of this method is that when the nonbonded term is turned to zero, atoms can pass through each other, while the connectivity of the molecule is maintained. It will be shown that such simulations, if a sufficient driving force is present (i.e., nuclear Overhauser effects restraints), can produce the correct stereoconfiguration (i.e., chiral center) as well as configurational isomer (i.e., cis/trans isomers).Lastly, a penalty term for coupling constants directly related to the Karplus curve has been plemented into the potential energy force field. The advantages of this method over the commonly used dihedral angle restraining are discussed. In particular, it is shown that with more than one coupling constant about a dihedral angle a great reduction of the allowed conformational space is obtained. © 1993 John Wiley & Sons, Inc.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 34 (1994), S. 559-563 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 36 (1995), S. 429-437 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformation of the antibiotic ureido-balhimycin has been investigated by proton nmr and refined with computer simulations. The dimeric structure cj ureido-balhimycin was established by unambiguous identification of 6 nuclear Overhauser effects (NOEs) as intermonomeric, out of the total of 186 NOEs observed. Via distance geometry calculations the antiparallel orientation of the two monomers was demonstrated. Further refinement by molecular dynamics simulations provided the essential hydrogen bonds and aromatic interactions responsible for interfacial stabilization. The computational protocol illustrated here (distance geometry to define the coarse topology and molecular dynamics for refinement) should find general applicability in the study of homodimers. © 1995 John Wiley & Sons, Inc.
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