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1

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Conformational analysis of bioactive peptides in reverse micelles as mimics of cell membrane environments (1995)

Quarzago, Daniela ; Moroder, Luis

Springer

International journal of peptide research and therapeutics 1 (1995), S. 171-177

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ISSN: 1573-3904

Keywords: Bioactive peptides ; Conformation ; Reverse micelles ; Circular dichroism ; Infrared spectroscopy

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Summary Conformational preferences of secretin as a model peptide have been analyzed by CD and IR spectroscopy in reverse micelles of AOT/isooctane/water and compared to those in aqueous TFE, in SDS micelles and in DMPG vesicles. Among the systems examined, reverse micelles and phospholipid vesicles displayed almost identical conformational equilibria. Very high lipid-to-peptide ratios can be obtained in reverse micelles with full retention of optical transparency, even at millimolar peptide concentrations, thus indicating this system to be an interesting mimic of cell membrane environments for spectroscopic analysis of bioactive peptide conformations.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00117953

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2

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Conformational and binding properties of chicken liver basic fatty acid binding protein in solutionA preliminary account of this work was presented at the II International Workshop on Fatty Acid Binding Proteins, Maastricht, The Netherlands August 31 to September 1, 1992, Abstracts, p. 46. (1994)

Schievano, Elisabetta ; Quarzago, Daniela ; Spadon, Paola ; [et al.]

New York : Wiley-Blackwell

Biopolymers 34 (1994), S. 879-887

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ISSN: 0006-3525

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: The conformation of basic fatty acid binding protein from chicken liver and the binding properties of the apo protein toward 11-dansylamino-undecanoic acid were investigated by CD and fluorescence spectroscopy. In one set of experiments the binding process was followed by the appearance of induced optical activity in the absorption region of the dansyl chromophore. In a second set of experiments the binding process was followed by the large enhancement of emission fluorescence of the dansyl fluorophore. From the saturation curves, the stoichiometry of the complex and the binding constant of the fatty acid to the protein were precisely determined. The values of the dissociation constant determined with the two methods were in excellent agreement: we obtained KD = (1.0 ± 0.1) · 10-6M in a 0.9 : 1 stoichiometry. The native conformation of the protein is remarkably stable in a variety of solvent systems, including acetonitrile-water, ethylene glycol-water, and dicxane-water of various compositions. The CD results also showed that the binding of the fatty acid does not induce any appreciable change in the protein conformation. In a mixture of water and 2,2,2-trifluoroethanol 1 : 9 (v/v), the native conformation collapses and a new ordered structure is formed, characterized by a high amount of α-helix. © 1994 John Wiley & Sons, Inc.

Additional Material: 9 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/bip.360340707

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3

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Conformational preferences of Leu-enkephalin in reverse micelles as membrane-mimicking environment (1997)

Rudolph-Böhner, Sabine ; Quarzago, Daniela ; Czisch, Michael ; [et al.]

New York : Wiley-Blackwell

Biopolymers 41 (1997), S. 591-606

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ISSN: 0006-3525

Keywords: Leu-enkephalin ; [13C, 15N]-backbone-labeled ; reverse micelles ; conformation ; CD ; FTIR ; nmr ; distance geometry ; Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Enkephalin represents one of the bioactive peptide molecules most extensively investigated both in solution and in the crystal state. Depending upon the environment chosen for such studies, three main conformational states were identified for this flexible, linear pentapeptide - i.e., an extended conformation, a single-bend, and a double-bend structure. Since CD and Fourier transform ir (FTIR) spectra of Leu-enkephalin solubilized in negatively charged reverse micelles of bis (2-ethylhexyl)sulfosuccinate sodium salt/isooctane/water were supportive of a restricted conformational space of the aromatic side chains and of a bended type fold, we have analyzed by nmr the conformational preferences of Leu-enkephalin in reverse micelles using a synthetic [13C, 15N]-backbone-labeled sample. The overall conformation derived from nuclear Overhauser effect spectroscopy (NOESY) and 15N-filtered rotating frame NOESY (ROESY) spectra and by distance geometry calculations is a double-bend fold of the backbone that is comparable to one of the known x-ray structures. Thereby the tyrosine side chain is inserted into the hydrophobic core of the reverse micelles in a restrained conformational space as well evidenced by NOEs between the aromatic ring protons and the surfactant. The proximity of the aromatic rings of tyrosine and phenylalanine indicate a preferred structure consistent with the postulated conformation of the opioid peptide in the δ-receptor-bound state. These results confirm the interesting and promising properties of reverse micelles as membrane mimetica. © 1997 John Wiley & Sons, Inc. Biopoly 41: 591-606, 1997

Additional Material: 11 Ill.

Type of Medium: Electronic Resource

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Redox-active bis-cysteinyl peptides. II. Comparative study on the sequence-dependent tendency for disulfide loop formation (1994)

Siedler, Frank ; Quarzago, Daniela ; Rudolph-Böhner, Sabine ; [et al.]

New York : Wiley-Blackwell

Biopolymers 34 (1994), S. 1563-1572

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ISSN: 0006-3525

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Bis (cysteinyl) octapeptides related to the active sites of the oxidoreductases protein disulfide isomerase (PDI), thioredoxin reductase (trr), glutaredoxin (grx), and thioredoxin (trx) were analyzed for their propensity to form the intramolecular 14-membered disulfide ring in oxidation experiments. The rank order of percentage of cyclic monomer formed in aqueous buffer (pH 7.0) at 10-3 M concentration was found to be very similar, but opposite to that of the Kox and, correspondingly, of the redox potentials of the native enzymes. Attempts to induce intrinsic conformational preferences of the peptides by addition of trifluoroethanol led to enhancements of β-turn structures as reflected by the CD and Fourier transform ir spectra. The induced secondary structure, instead of aligning the tendencies of the excised fragments for loop formation with those of the intact proteins, was found to suppress the differences by significantly increasing the preference for cyclic monomers (≈ 90%). Similarly, operating under denaturing conditions, i.e., in 6M guanidinium hydrochloride, only for the trx peptide was the statistical product distribution obtained. For the remaining peptides, again a strong increase of cyclic monomer contents was observed that could not be correlated with dissolution of β-sheet type aggregates. The CD spectra are more consistent with the presence of ordered structure to some extent, possibly resulting from an hydrophobic collapse of the sparingly soluble peptides. The results of the oxidation experiments further support previous findings from thiol disulfide interchange equilibria, which clearly revealed a decisive role of the characteristic thioredoxin structural motif in dictating the redox properties of the enzymes. Point mutations in the active sites of the oxidoreductases allowed us to affect their redox potentials strongly, but apparently only in the constraint form of the three-dimensional structure as similar exchanges in the excised fragments did not produce the expected effect. This observation contrasts with numerous reports that the conformation of short disulfide loops is mainly dictated by the amino acid sequence. © 1994 John Wiley & Sons, Inc. © 1994 John Wiley & Sons, Inc.

Additional Material: 7 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/bip.360341114

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Redox-active bis-cysteinyl peptides. I. Synthesis of cyclic cystinyl peptides by conventional methods in solution and on solid supports (1994)

Musiol, Hans-Jürgen ; Siedler, Frank ; Quarzago, Daniela ; [et al.]

New York : Wiley-Blackwell

Biopolymers 34 (1994), S. 1553-1562

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ISSN: 0006-3525

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Notes: Cyclic mono-cystinyl active-site fragments of thioredoxin and thioredoxin reductase were synthesized as N-acetyl and C-amide octapeptides by conventional methods of peptide synthesis in solution and on solid supports. Using a side-chain protection based on acid-labile tert-butanol-derived groups and on the S-tert-butylthio unsymmetric disulfide for the thiol functions, in combination with Nα-Z- or Nα-Nps derivatives in the chain elongation steps, the synthesis in solution was carried out in straightforward manner yielding the fully protected octapeptides as well characterized compounds. Upon deprotection with trifluoroacetic acid and reduction of the unsymmetrical disulfides with tri-butylphosphine, the resulting bis-cysteinyl-octapeptides were oxidized in dimethylformamide with azodicarboxylic acid di-tert-butyl ester to produce the desired cyclic compounds in good overall yields. For the synthesis on solid supports a similar acid-labile side-chain protection was applied in combination with the Nα 9-flourenylmethyoxycarbonyl derivatives in the chain elongation steps. Thereby acylations were performed with the related amino acid N-car-boxyanhydrides (UNCAs) or by the O-(1H-benzotriazol-1-yl)-N,N,N′,N′-tetramethyl-uronium-tetrafluoroborate/1-hydroxybenzotriazole (TBTU/HOBt) procedure. The solid phase synthesis of the two octapeptides led to unexpected difficulties in terms of recovery of peptidic material from the resins in the final acidolytic cleavage step as well as of racemization at the level of the cysteine residues by the TBTU/HOBt coupling method. Racemization was efficiently suppressed by employing the related pentafluorophenyl ester and this method led to crude octapeptide products of a degree of purity comparable to those obtained by the synthesis in solution. However, the recovery of the peptides from the resin, i.e., irreversible reattachment of cleaved peptidic material via alkylation of various side-chain functions, could not be avoided even using the most efficient scavengers or their cocktails. © 1994 John Wiley & Sons, Inc. © 1994 John Wiley & Sons, Inc.

Additional Material: 2 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/bip.360341113

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