Conformational difference between diastereomers of Dnp-Val-Aib-Gly-Leu-pNA studied by x-ray crystal analyses

Turn and helical peptide spacers: Combined distance and angular dependencies in the exciton-coupled circular dichroism of intramolecularly interacting bis-porphyrins

In a previous study we examined by the exciton-coupled circular dichroic method the distance effect generated by three-rigid-turn and helical-peptide spacers. In this connection porphyrins were confirmed to be excellent reporter chromophores. In the present investigation we have completed this research by expanding the original analysis to the assessment of the combined role of the chromophore distance and orientation with use of the same porphyrin derivatives and additional four analogous spacers of different main-chain lengths. We find that not only the intramolecular separation of the chromophores, but the angular dependence between the directions of their effective transition moments as well, are responsible for the onset and modulation of the intensity of the exciton-coupling phenomenon of the porphyrin Soret band.

Metal ion-binding ability of tetrapeptides containing alpha-aminoisobutyric acid

alpha-Aminoisobutyric acid (Aib), one of the Calpha,alpha-disubstituted glycines, is a sterically hindered amino acid that acts as a conformational constraint in peptides. However, studies for the application of the ability of Aib to control conformation are quite few. The paper focuses on the molecular recognition ability of acyclic oligopeptides containing Aib. Liquid-liquid extraction of nine kinds of metal ions from aqueous layers to nonpolar organic layers with acyclic tetrapeptides, X-Trp-Xaa2-Gly-Xaa4-NH-Ar (X = H or C6H5CH2OCO (Z), Xaa2 = Aib or Gly, Xaa4 = Leu or Ala, Ar = phenyl or 3,5-dimethylphenyl) was examined using picrate as the anion of ion pairs. The extraction behaviour of the metal ions with the tetrapeptides was investigated in the pH range from 3 to 9. In the case of basic pH regions, Cu(II) and Ag(I) were effectively extracted with Trp-Aib-Gly-Leu-NH-Ar. Pd(II) was specifically extracted with Trp-Aib-Gly-Leu-NH-Ar in acidic pH regions. The extraction percent (%E) of the peptide host, which has a 3,5-dimethylphenyl group, was even larger than that of the host, which has a phenyl group. Moreover, Pd(II) was extracted with a peptide host which has Leu and a 3,5-dimethylphenyl group in the absence of picrate as the anion of ion pairs. The free alpha-amino group, the turn conformation and the hydrophobicity of peptide molecules were important factors for the extraction of the metals.

Distance dependency of exciton coupled circular dichroism using turn and helical peptide spacers

Porphyrins are promising chromophores for the investigation of the still unexplored area of 3-dimensional structural studies of proteins by using the exciton coupled circular dichroism (CD) method. The synthesis, conformational characterization by FTIR absorption and (1)H-NMR, and CD properties are described for a model bis-porphyrin system based on homooligo-[L-(alphaMe)Val](n) peptides as rigid spacers. In particular, the coupled CD phenomenon is experimentally detected, the intensity of which is modulated by the interchromophoric distance. These results extend and integrate those already reported with steroid, dimeric steroid, and brevetoxin bridges.

Characteristic molecular packing in the crystal structure of tert-butoxycarbonyl-L-phenylalanyl-L-methionine methyl ester

The molecular conformation and association of the peptide Boc-L-Phe-L-Met-OMe have been studied in the solid state by X-ray diffraction. The peptide crystallizes in the orthorhombic system, space group P2(1)2(1)2(1), with cell parameters of a = 9.821(2), b = 25.394(6), c = 28.714(8) A, V = 7161(3) A3. The structure has been solved by direct methods and refined to a final R of 0.079 for 5464 independent reflections with Fo > or = sigma(Fo). The crystal consists of three independent molecular conformations per asymmetric unit. Respective peptide backbones adopt an extended conformation with the side-chains of Phe and Met residues being arranged below and above the backbone chains. Contrary to the sheet structure most frequently observed in the crystal packing of the extended peptide conformations, three independent molecules lie spirally along the c-axis and form a pin-wheel-like crystal packing. The sheet structures formed by two of three independent molecules are almost at right angles to the backbone of the remaining molecule. This molecular packing mode would provide a possible interaction model between the intersecting beta-sheet structure and single-strand structure of polypeptide.