Biomedical subjects

F Schotte

Publications and source records attributed to F Schotte.

5 recordsLinked to original sources

PubMed2001

A molecular movie at 1.8 A resolution displays the photocycle of photoactive yellow protein, a eubacterial blue-light receptor, from nanoseconds to seconds.

The photocycle of the bacterial blue-light photoreceptor, photoactive yellow protein, was stimulated by illumination of single crystals by a 7 ns laser pulse. The molecular events were recorded at high resolution by time-resolved X-ray Laue diffraction as they evolved in real time, from 1 ns to seconds after the laser pulse. The complex structural changes during the photocycle at ambient temperature are displayed in a movie of difference electron density maps relative to the dark state. The step critical to entry into the photocycle is identified as flipping of the carbonyl group of the 4-hydroxycinnamic acid chromophore into an adjacent, hydrophobic environment rather than the concomitant isomerization about the double bond of the chromophore tail. The structural perturbation generated at the chromophore propagates throughout the entire protein as a light-induced "protein quake" with its "epicenter" at the carbonyl moiety of the chromophore.

Bacterial Proteins↗

PubMed2001

Visualizing photochemical dynamics in solution through picosecond x-ray scattering.

A photoexcited state of molecular iodine in solution is observed using diffuse x-ray scattering at a synchrotron source. The measured changes in the diffuse scattering profile were consistent with earlier models of iodine's photodissociation and geminate recombination reaction, for which the recombined A/A(') state has a 0.4 A greater interatomic spacing than the resting state and has a lifetime of 500 ps in CH2Cl2. This technique should find application in the study of increasingly complicated photochemical systems which undergo structural rearrangements following rapid photolysis.

Journal Article↗

PubMed2001

Picosecond X-ray diffraction probed transient structural changes in organic solids.

In this Letter, we report on the experimental characterization of the geometry of short-lived electronically excited states in organic solids by time-resolved x-ray diffraction. Here, the structure factor of the organic crystal is measured as a function of time. Since this technique gives complete structural information, it is a very useful tool for learning more about atom motions on the excited-state energy surface-"beyond" the broad band typical of conventional spectroscopy. Although we used molecular crystals rather than free molecules, the compounds show detectable transient structural changes on the ps to ns time scale in our study.

Journal Article↗

PubMed2000

Extraction of accurate structure-factor amplitudes from Laue data: wavelength normalization with wiggler and undulator X-ray sources.

Wavelength normalization is an essential part of processing of Laue X-ray diffraction data and is critically important for deriving accurate structure-factor amplitudes. The results of wavelength normalization for Laue data obtained in nanosecond time-resolved experiments at the ID09 beamline at the European Synchrotron Radiation Facility, Grenoble, France, are presented. Several wiggler and undulator insertion devices with complex spectra were used. The results show that even in the most challenging cases, such as wiggler/undulator tandems or single-line undulators, accurate wavelength normalization does not require unusually redundant Laue data and can be accomplished using typical Laue data sets. Single-line undulator spectra derived from Laue data compare well with the measured incident X-ray spectra. Successful wavelength normalization of the undulator data was also confirmed by the observed signal in nanosecond time-resolved experiments. Single-line undulators, which are attractive for time-resolved experiments due to their high peak intensity and low polychromatic background, are compared with wigglers, based on data obtained on the same crystal.

Journal Article↗

PubMed1998

Energy transduction on the nanosecond time scale: early structural events in a xanthopsin photocycle.

Photoactive yellow protein (PYP) is a member of the xanthopsin family of eubacterial blue-light photoreceptors. On absorption of light, PYP enters a photocycle that ultimately transduces the energy contained in a light signal into an altered biological response. Nanosecond time-resolved x-ray crystallography was used to determine the structure of the short-lived, red-shifted, intermediate state denoted [pR], which develops within 1 nanosecond after photoelectronic excitation of the chromophore of PYP by absorption of light. The resulting structural model demonstrates that the [pR] state possesses the cis conformation of the 4-hydroxyl cinnamic thioester chromophore, and that the process of trans to cis isomerization is accompanied by the specific formation of new hydrogen bonds that replace those broken upon excitation of the chromophore. Regions of flexibility that compose the chromophore-binding pocket serve to lower the activation energy barrier between the dark state, denoted pG, and [pR], and help initiate entrance into the photocycle. Direct structural evidence is provided for the initial processes of transduction of light energy, which ultimately translate into a physiological signal.

Bacterial Proteins↗