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Sleeping sickness is a fatal disease caused by the protozoan parasite Trypanosoma brucei (Tb). Inosine-5’-monophosphate dehydrogenase (IMPDH) has been proposed as a potential drug target, since it maintains the balance between guanylate deoxynucleotide and ribonucleotide levels that is pivotal for the parasite. Here we report the structure of TbIMPDH at room temperature utilizing free-electron laser radiation on crystals grown in living insect cells. The 2.80 Å resolution structure reveals the presence of ATP and GMP at the canonical sites of the Bateman domains, the latter in a so far unknown coordination mode. Consistent with previously reported IMPDH complexes harboring guanosine nucleotides at the second canonical site, TbIMPDH forms a compact oligomer structure, supporting a nucleotide-controlled conformational switch that allosterically modulates the catalytic activity. The oligomeric TbIMPDH structure we present here reveals the potential of in cellulo crystallization to identify genuine allosteric co-factors from a natural reservoir of specific compounds., Trypanosoma brucei inosine-5′-monophosphate dehydrogenase (IMPDH) is an enzyme in the guanine nucleotide biosynthesis pathway and of interest as a drug target. Here the authors present the 2.8 Å room temperature structure of TbIMPDH determined by utilizing X-ray free-electron laser radiation and crystals that were grown in insect cells and find that ATP and GMP are bound at the canonical sites of the Bateman domains.

The programXVisis designed for interactive demonstration of different diffraction issues, such as reciprocal-space construction, connection between real and reciprocal spaceviadiffraction phenomena, different methods of reciprocal-space scanning, accessible reciprocal-space regions for coplanar and noncoplanar diffraction for both transmission and reflection geometries,N-beam diffraction phenomena, reciprocal space for two-layered systems and experimental examples. All demonstrations are calculated using real structure parameters. For better information representation, the program displays most demonstrations in real and reciprocal space simultaneously. The program is open source and can be downloaded from http://x-ray.net.ua/xvis.html.

The changes of structural and photoluminescence (PL) characteristics of MBE-grown CdZnSe/ZnSe single quantum well (QW) structures caused by Cd/Zn interdiffusion were studied by high-resolution X-ray diffraction (HRXRD) and low-temperature PL methods. The PL investigations showed that the increase of Cd content in the QW resulted in the increase of the depth of potential fluctuations in the QW as well as in the decrease of ZnSe cap layer band gap (up to several meV). The HRXRD scans as well as reciprocal space maps measured for symmetrical and asymmetrical diffractions revealed the formation of CdZnSe layers near the QW/ZnSe interface with Cd content of order of several percents. It is found that in some samples, the Cd profile in these layers is rather smooth while in others it is quite abrupt. In the latter case, the partial strain relaxation can occur in these layers.

The results of the photoluminescence (PL) and the high-resolution X-ray diffraction (HRXRD) investigations of point and extended defects in strained InGaAs(N)Sb/GaAs quantum well (QW) structures grown at 478–505 °C are presented. HRXRD studies prove a good quality of heterointerfaces in all samples that is attributed to Sb-surfactant effect. The PL investigations show that the increase of the growth temperature of N-containing QWs leads to the increase of potential fluctuations in QW due to the increase of composition disorder. In the PL spectra an intense band caused by excitonic transitions related with N-related clusters in GaAs barriers is found. HRXRD mapping in symmetrical 004 reflections reveals the oscillation of interference picture in [110] direction around the normal to (100) surface known as a “wiggle”. The mapping indicates the formation of elastically coupled domains which are elongated in [¯110] direction and are supposed to be cased by lateral composition modulations in the QW. It is proposed that a “wiggle” explained by the change of slopes of crystallographic planes with the depth is the result of competition of two factors — a symmetry of the surface stress tensor and a symmetry of bulk elastic moduli of a substrate material.

A major challenge in high-resolution x-ray free-electron laser-based coherent diffractive imaging is the development of aerosol injectors that can efficiently deliver particles to the peak intensity of the focused X-ray beam. Here, we consider the use of a simple convergent-orifice nozzle for producing tightly focused beams of particles. Through optical imaging we show that 0.5 μm particles can be focused to a full-width at half maximum diameter of 4.2 μm, and we demonstrate the use of such a nozzle for injecting viruses into a micro-focused soft-X-ray FEL beam.

Current hard X-ray free-electron laser (XFEL) sources can deliver doses to biological macromolecules well exceeding 1 GGy, in timescales of a few tens of femtoseconds. During the pulse, photoionization can reach the point of saturation in which certain atomic species in the sample lose most of their electrons. This electronic radiation damage causes the atomic scattering factors to change, affecting, in particular, the heavy atoms, due to their higher photoabsorption cross sections. Here, it is shown that experimental serial femtosecond crystallography data collected with an extremely bright XFEL source exhibit a reduction of the effective scattering power of the sulfur atoms in a native protein. Quantitative methods are developed to retrieve information on the effective ionization of the damaged atomic species from experimental data, and the implications of utilizing new phasing methods which can take advantage of this localized radiation damage are discussed.

Variations of the characteristics of Sb-surfactant assisted grown InGaAsN/GaAs single quantum wells (QWs) in dependence on QW growth temperature ( T GR = 442–505 °C) are investigated by the photoluminescence (PL) and high-resolution X-ray diffraction (HRXRD) methods. The QWs grown at ∼480 °C demonstrated optimal PL characteristics, namely the highest PL intensity and small potential fluctuations. A good quality of heterointerfaces is proved by HRXRD. These structures emit at ∼1.29 μm at 300 K and are promising for application in long wavelength opto-electronic devices. The good structural properties of these QWs are assigned to Sb surfactant effect that allows shifting of the T GR to higher temperatures without significant alloy decomposition. The increase of T GR in its turn results in the decrease of the density of nonradiative defects that are the specific feature of low temperature growth.

The results of investigation of In 0.3 Ga 0.7 As/GaAs superlattice by high-resolution X-ray scattering are presented. The influence of lattice distortion on diffraction curves (DC) were analyzed with dynamical diffraction theory. It allowed to explain azimuth dependence of experimental diffraction curves. Anisotropic changes in the shape of InGaAs lattice unit cell were shown and measured. The influence of smooth borders between hetero-layers were analyzed. Comparative analysis of different gradient functions on the hetero-border influence on diffraction curves was done. Parameters of heterojunction in investigated samples were determined with the help of DC modelling.