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  • 1
    ISSN: 1075-2617
    Keywords: Hormone biosynthesis ; ocytocin ; prohormone ; proteolytic processing ; β-turn ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthetic peptides reproducing the proteolytic processing site of pro-ocytocin were studied by different spectroscopic techniques, including circular dichroism, Fourier tranform infrared absorption, and mono and bidimensional nuclear magnetic resonance, in order to ascertain the possible role of three-dimensional structure in the recognition process by maturation enzymes. Experimental results were compared with energy minimization calculations and suggest that: (i) the region situated on the N-terminus of the Lys-Arg doublet may form a β-turn; (ii) the sequential organization of the residues participating in the β-turn determines the privileged relative orientation of the basic amino acid sidechains and the subtype of turn; and (iii) the peptide segment situated on the C-terminal side of the dibasic doublet may assume a helix arrangement. These findings, in spite of the limitations connected to the flexibility of linear peptides, seem to substantiate the hypothesis that structural motifs around the cleavage site could be important for recognition and processing. However, a straightforward correlation between details of the secondary structure and the in vitro reactivity toward a putative convertase is not yet possible.
    Additional Material: 7 Ill.
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  • 2
    ISSN: 1075-2617
    Keywords: (αMe) amino acids ; CD spectroscopy ; 310-helix ; peptide 3D-structure ; X-ray structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The terminally blocked tetrapeptide pBrBz-[D-(αMe)Leu]2-D-(αMe)Val-D-(αMe)Leu-OtBu is folded in the crystal state in a left-handed 310-helical structure stabilized by two consecutive 1 ← 4 C=O⃛H—N intramolecular H-bonds, as determined by X-ray diffraction analysis. A CD study strongly supports the view that this conformation is also that largely prevailing in MeOH solution. A comparison with the published conformation of pBrBz-[D-(αMe)Leu]4-OtBu indicates that incorporation of a single internal β-branched (αMe)Val guest residue into the host homo-tetrapeptide from the γ-branched (αMe)Leu residue is responsible for a dramatic structural perturbation, i.e. an inversion of the 310 screw sense from right to left-handed.
    Additional Material: 2 Ill.
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  • 3
    ISSN: 1075-2617
    Keywords: β-turn ; cyclic amino acid ; 310-helix ; peptide conformation ; X-ray diffraction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of N- and C-protected, monodispersed homo-oligopeptides (to the pentamer level) from the cycloaliphatic Cα,α,-dialkylated glycine 1-aminocyclononane-1-carboxylic acid (Ac9c) and two Ala/Ac9c tripeptides have been synthesized by solution methods and fully characterized. The conformational preferences of all the model peptides were determined in deuterochloroform solution by FT-IR absorption and 1H-NMR. The molecular structures of the amino acid derivatives mClAc-Ac9c-OH and Z-Ac9c-OtBu, the dipeptide pBrBz-(Ac9c)2-OtBu, the tetrapeptide Z-(Ac9c)4-OtBu, and the pentapeptide Z-( Ac9c)5-OtBu were determined in the crystal state by X-ray diffraction. Based on this information, the average geometry and the preferred conformation for the cyclononyl moiety of the Ac9c residue have been assessed. The backbone conformational data are strongly in favour of the conclusion that the Ac9c residue is a strong β-turn and helix former. A comparison with the structural propensity of α-aminoisobutyric acid, the prototype of Cα,α-dialkylated glycines, and the other extensively investigated members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n=3-8) is made and the implications for the use of the Ac9c residue in conformationally constrained analogues of bioactive peptides are briefly examined. © 1997 European Peptide Society and John Wiley & Sons, Ltd.J. Pep. Sci. 3: 367-382No. of Figures: 10. No. of Tables: 6. No. of References: 62
    Additional Material: 10 Ill.
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  • 4
    ISSN: 0006-3525
    Keywords: molecular scaffolds ; β-turn ; tachykinin antagonist ; x-ray ; nmr ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We recently reported the rational design, synthesis, and structural characterization of the most potent and selective peptide-based neurokinin A antagonist thus far described: cyclo(Met1-Asp2-Trp3-Phe4-Dap5-Leu6)cyclo(2β-5β). Its bicyclic structure is characterized by a type I and a type II two β-turn around Trp3-Phe4 and Leu6-Met1, respectively. In order to understand whether the two different β-turned structures are determined by the bicyclic structure or by the amino acid type at the corner positions, we have synthesized the pseudosymmetrical analogue cyclo(Phe1-Asp2-Trp3-Phe4-Dap5-Trp6)cyclo(2β-5β). The structural characterization in the crystal state and in solution, here reported, gives an experimental evidence that the backbone of the bicyclic structure is a rigid scaffold that can be used to build both a type I and type II β-turn independently from the amino acid composition. © 1997 John Wiley & Sons, Inc. Biopoly 40: 505-518, 1996
    Additional Material: 8 Ill.
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