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Schlagwörter:
(4-aminomethyl)phenylazobenzoic acid; cyclic peptides; photoisomerization; conformation analysis; NMR spectroscopy
Zusammenfassung:
In previous studies we have shown that light-induced cis/trans isometization of the azobenzene moiety in cyclo-[Ala-Cys-Ala- Thr-Cys-Asp-Gly-Phe-AMPB] [AMPB: (4- aminomethyl)phenylazobenzoic acid] leads both in the monocyclic and in the oxidized bicyclic form to markedly differentiated conformational states in DMSO, a fact that lends itself for photomodulation of the redox potential of such bis-cysteinyl- peptides. For this purpose water-soluble systems are required, and this was achieved by replacing three residues outside the Cys-Ala-Thr-Cys active-site motif of thioredoxin reductase with lysines. The residting cyclo-[Lys-Cys-Ala-Thr-Cys-Asp-Lys-Lys- AMPB]fully retains its photoresponsive properties in water as well assessed by in, and CD measurements. Paralleling results of the previously investigated azobenzene-containing cyclic peptides, the trans --> cis isomerization of the water-soluble monocyclic and oxidized bicyclic peptide is accompanied by a marked transition front a well-defined conformation to an ensemble of possible conformations. However, the conformational preferences are very dissimilar from those of the DMSO-soluble peptides. In fact, hydrogen bonds as well as secondary structure elements were found that change in the mono- and bicyclic peptide upon irradiation. The photo switch between different turn types and hydrogen bonding networks offers the structural rational for the significantly differentiated redox potentials, but also the possibility of Monitoring by femtosecond uv-vis and ir spectroscopy fast and ultra fast backbone rearrangement proccsses following the electronic trans --> cis isomerization. (C) 2002 Wiley Periodicals, Inc.
