title: Photomodulation of conformational states. I. Mono- and bicyclic peptides with (4-amino)phenylazobenzoic acid as backbone constituent.
abstract: The thioredoxin reductase active-site fragment H-Ala-Cys-Ala-Thr-Cys-Asp-Gly-Phe-OH [134-141], which is known for its high tendency to assume an almost identical conformation as in the intact enzyme, was backbone cyclized with the photoresponsive (4-amino)phenylazobenzoic acid (APB) to produce a monocyclic and disulfide-bridged bicyclic APB-peptide. Light-induced reversible cis/trans isomerization occurs at identical extents in both the linear and the two cyclic forms. Nuclear magnetic resonance conformational analysis clearly revealed that in the bicyclic APB-peptide both as a trans- and cis-azo-isomer the constraints imparted by the bicyclic structure do not allow the molecule to relax into a defined low energy conformation, thus making the molecule a frustrated system that flip-flops between multiple conformational states. Conversely, the monocyclic APB peptide folds into a well-defined lowest energy structure as a trans-azo-isomer, which upon photoisomerization to the cis-azo configuration relaxes into a less restricted conformational space. First femtosecond spectroscopic analysis of the dynamics of the photoreaction confirm a fast first phase on the femtosecond time scale related to the cis/trans isomerization of the azobenzene moiety followed by a slower phase in the picosecond time scale that involves an adjustment of the peptide backbone. Due to the well- defined photoresponsive two-state transition of this monocyclic peptide molecule, it represents a model system well suited for studying the ultrafast dynamics of conformational transitions by time-resolved spectroscopy.
authors.affiliation: Max-Planck Institut für Biochemie, 82152 Martinsried, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Renner
authors.forename: R
authors.initials: R
authors.lastname: Behrendt
authors.forename: S
authors.initials: S
authors.lastname: Spörlein
authors.forename: J
authors.initials: J
authors.lastname: Wachtveitl
authors.forename: L
authors.initials: L
authors.lastname: Moroder
mesh_terms: D062365:Aminobenzoates / Q000737:chemistry* / Q000528:radiation effects*; D001391:Azo Compounds / Q000737:chemistry* / Q000528:radiation effects*; D002942:Circular Dichroism; D007536:Isomerism; D008027:Light; D008958:Models, Molecular; D008968:Molecular Conformation / Q000528:radiation effects; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000737:chemistry / Q000528:radiation effects; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000528:radiation effects; D010777:Photochemistry / Q000379:methods; D017433:Protein Structure, Secondary; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D013880:Thioredoxin-Disulfide Reductase / Q000737:chemistry; D013997:Time Factors; D062366:para-Aminobenzoates
chemical_list: C417554:(4-amino)phenylazobenzoic acid; D062365:Aminobenzoates; D001391:Azo Compounds; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D062366:para-Aminobenzoates; D013880:Thioredoxin-Disulfide Reductase