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  • 1
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 24 (1985), S. 961-978 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The x-ray structure of Boc-L-Ala-Aib-Ala-Aib-Ala-Glu(OBzl)-Ala-Aib-Ala-Aib-Ala-OMe(I) represents the first α-helix determined by direct methods. This undecapeptide is a model of the N-terminus of alamethicin, and it exhibits voltage-dependent pores in bilayer membranes at a higher voltage and concentration than alamethicin. The molecule crystallizes in the monoclinic space group P21 with a = 10.602(1), b = 23.884(3), c = 13.622(1) Å, β = 95.61(6)°, and Z = 2. It adopts a right-handed α-helical conformation in the solid state with intramolecular 5 → 1 hydrogen bonds. An additional intramolecular hydrogen bond is bifurcated, forming a stronger 4 → 1 interaction (i.e., a β-turn III) and a weaker 5 → 1 interaction, thus prolonging the α-helical part up to 9 residues. The α-helix radius of 2.1 Å, the height per residue (distance Ni … Ni + 4) of 1.53 Å, the resulting length of the α-helical part of 13.8 Å (9 residues) resp. 15.3 Å (10 residues), the van der Waals radius (4.7 Å), and the minimal diameter of pores formed by aggregation of 3-10 α-helices were calculated omitting the Glu(OBzl) side chain. In the crystal, the α-helices are linked head to tail via two hydrogen bridges forming continuous chains. Adjacent helices are oriented in antiparallel with their helix axes and have only van der Waals contacts.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Boc-L-Leu-Aib-Pro-Val-Aib-Aib-Glu(OBzl)-Gln-Phl (Boc = t-butyloxycarbonyl, Aib = α-aminoisobutyric acid, Bzl = benzyl, Phl = phenylalaninol), C59H90N10O14, the protected C-terminal nonapeptide with the sequence 12-20 of alamethicin, crystallizes in the orthorhombic space group P212121 with a = 15.666, b = 16.192, c = 26.876 Å, and Z = 4. The molecular conformation is right-handed helical with three α-(5 → 1 hydrogen bonds) and three β-turns (4 → 1 hydrogen bonds). All but two of the hydrogen bonds are significantly longer than the usual value and show bifurcation to some extent. The α/310r-helical nonapeptide molecules are arranged head-to-tail along the a direction. The resulting linear antiparallel chains are linked by a weak intermolecular hydrogen bridge, thus forming a two-dimensional layer structure in the ab plane. The conformation of this nonapeptide is almost identical with that of the corresponding C-terminal part found by x-ray crystallography of the eicosapeptide alamethicin.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 21 (1990), S. A78 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stepwise synthesis and conformational studies of the N-terminal helical partial sequence of the membrane-modifying polypeptide antibiotic alamethicin are described. The polyoxyethylen esters of the fragments N-t-Boc-L-Pro-Aib-Ala-Gln-Aib-Val-Aib-Gly-OH and N-Ac-Aib-L-Pro-Aib-Ala-Aib-Ala-Gln-Aib-Val-Aib-Gly-OH are synthesized using polyoxyethylene (molecular mass 10,000) as solubilizing support. CD spectra of each intermediate in ethanol show α-helix formation of the N-protected peptide polymers beginning with the nonapeptide and of the N-protonated sequences beginning with the decapeptide. Compared to the helix of alamethicin, temperature- and solvent-dependent CD measurements indicate analogous conformational behavior. The results suggest that in lipophilic media the alamethicin helix can extend the full length of the partial sequence between the two proline residues and that aqueous media favor an increase of random-coil conformation.For model studies of the particular lipid interaction of alamethicin, the stepwise synthesis of peptides with the alternating (Aib-L-Ala)n sequence (n = 1-7) was carried out on a polyoxyethylene support (molecular mass 6000). CD and ORD studies in ethanol showed a change from the random coil to a right-handed α-helix with increasing peptide length. This change is observed for the N-protected peptides at a chain length of 8 residues and for the N-protonated peptides at a length of 9 residues. The comparison of the CD data of free and polyoxyethylene-bound peptides revealed that the solubilizing polymeric support cannot induce conformational changes. The intensities of the CD bands of t-Boc-(Aib-L-Ala)n-OPOE (n ≥ 6) are higher than those of alamethicin, and these model peptides show similar temperature and solvent inducible changes of their helix contents.
    Additional Material: 8 Ill.
    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: The conformational analysis of the CD spectrum is reported for the synthetic and membrane-modifying nonadecapeptide analog of alamethicin N-t-Boc-(Aib-L-Ala)5-Gly-Ala-Aib-Pro-Ala-Aib-Aib-Glu(OBzl)- Gln-OMe. The CD data are evaluated according to three different methods and are discussed with respect to those obtained from natural alamethicin and suitable models such as N-t-Boc-(Aib-L-Ala)7-OPOE, fragments of the synthetic nonadecapeptide, and the hexadecapeptide N-t-Boc-(Aib-L-Ala)5-Pro-Ala-Aib-Aib-Glu(OBzl)-Gln-OMe. The synthetic nonadecapeptide with the longer helical region exhibits membrane activities comparable to those of alamethicin, whereas the hexadecapeptide with the shorter helix is inactive.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 241-246 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C-, 1H-nmr, CD, and x-ray crystallography revealed β-turns of type III for Boc-Gly-L-Ala-Aib-OMe, Boc-L-Ala-Aib-L-Ala-OMe; the 310-helix for Boc-Aib-L-Ala-Aib-L-Ala-Aib-OMe; and antiparallel arranged α-helices for Boc-L-Ala-Aib-Ala-Aib-Ala-Glu(OBzl)-Ala-Aib-Ala-Aib-Ala-OMe. An N-terminal rigid α-helical segment is found in the polypeptide antibiotics alamethicin, suzukacillin, and trichotoxin. The α-helix dipole is essential for their voltage-dependent pore formation in lipid bilayer membranes, which is explained by a flip-flop gating mechanism based on dipole-dipole interactions of parallel and antiparallel arranged α-helices within oligomeric structures.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0021-9304
    Keywords: growth substrates ; laminin ; adhesion peptides ; electrochemical coupling ; cell adhesion ; axonal growth ; surface functionalization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Interactions between cultured nerve cells and surfaces are of importance for the implantation of biocompatible electrode materials such as glassy carbon (GC). Since implants serve as recording sensors in prosthetic neuroscience, we investigated whether coating electrodes with certain laminin derivatives containing the peptide sequences SIKVAV, CDPGYIGSR, PDSGR, YFQRYLI, and RNIAEIIKDA influences neuronal adhesion and neurite outgrowth in vitro. The coating of GC was performed by electrochemical polymerization and, for comparison, by adsorption or covalent coupling. Electrochemical polymerization is suitable for the coupling of peptides to GC, as shown by amino acid analysis and sequencing. Embryonic chicken retinal ganglion cells and brain cells (days E7 or E17) were used for both attachment and growth studies. Surfaces made by electrochemical polymerization of peptides were more efficient than those made by adsorption or covalent coupling of peptides. Synthetic cyclic peptide derivatives of CDPGYIGSR and 18-mer SIKVAV were found to be more efficient than the linear peptides. Competitive effects that resulted in a decreased cell attachment could be found upon application of soluble peptides. Nevertheless, irrespective of the method of coating, peptides were less efficient compared with the whole laminin molecule, as expected from its multiple adhesion sites. When small GC pins were implanted into the brain of E17 chicken after coating with the 18-mer SIKVAV peptide, nerve cell attachment was observed in vivo. The results suggest that chronically implantable materials may exert a higher neurocompatibility when coated with synthetic peptides. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 278-288, 1998.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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