Symmetry breaking by enzyme-catalyzed epoxide hydrolysis

Janfalk Carlsson et al. [IUCrJ (2018), 5, 269–282] describe studies on factors determining selective ring opening of methylstyrene oxide stereoisomers by the epoxide hydrolase StEH1. The stereo-differentiating step is selective hydrolysis of an alkylated intermediate formed by reaction of the epoxide with an aspartyl residue.

Identification of ions in experimental electrostatic potential maps

Cryo-EM maps are sensitive to total nuclear and electron charges of a species whereas X-ray crystallography only visualizes electrons without a nuclear contribution. Cryo-EM can be used to identify charge and chemical identity.

Using cryo-electron microscopy maps for X-ray structure determination

A hybrid method is presented that provides an automated tool for X-ray structure determination using a cryo-EM map as the starting point.

Dummy-atom modelling of stacked and helical nanostructures from solution scattering data

A bead-modelling approach is presented to determine the structural motifs of helical and rod-like systems from small-angle solution scattering data. The implemented algorithm is verified using analytical models and is further applied to reconstruct from experimental scattering data the building block of a self-assembled peptide double helix.

Direct shape determination of intermediates in evolving macromolecular solutions from small-angle scattering data

The low-resolution shape of an unknown intermediate in an evolving nanostructured system is directly reconstructed from a global fit of the solution scattering data recorded during the process.

Model-free reconstruction of magnetic correlations in frustrated magnets

A new method for direct quantification of magnetic correlations in frustrated magnets is developed based on analysis of neutron total scattering data.

Monoclinic distortion, polarization rotation and piezoelectricity in the ferroelectric Na_0.5Bi_0.5TiO₃

Time-resolved high-resolution X-ray diffraction has been implemented to investigate how monoclinic distortion in the ferroelectric Na_0.5Bi_0.5TiO₃ responds to an external electric field. The results strongly favour the model of electric-field-induced polarization rotation and predict that even a sub-coercive electric field can change the direction of the spontaneous polarization vector by 30° or more.

Towards a practical implementation of X-ray ghost imaging with synchrotron light

A practical experimental procedure for transmission X-ray ghost imaging (XGI) using synchrotron light is presented. The authors demonstrate the method, discuss data acquisition and analysis, and measure the point-spread function of an XGI system. The generalization of the methods for future experiments is also discussed.

Chlamydia protein Pgp3 studied at high resolution in a new crystal form

Pgp3, a protein implicated in the sexually transmitted disease chlamydia, is described in a new crystal structure. It comprises a three-domain multi-macromolecular complex with two misaligned threefold axes; this comprised a unique challenge that has not been encountered before. A specific intermolecular interaction, possibly of functional significance in receptor binding in chlamydia, might allow the design of a new chemotherapeutic agent against chlamydia.

Protonated nucleobases are not fully ionized in their chloride salt crystals and form metastable base pairs further stabilized by the surrounding anions

Charge-density studies of cytosinium chloride, adeninium chloride hemihydrate and guaninium dichloride crystals based on ultra-high-resolution X-ray diffraction data and extensive theoretical calculations are presented. The studies confirm the importance of electrostatic interactions in ionic crystals and show how counterintuitive they can be for protonated nucleobases of like charge.

Sr₂Pt_8−xAs: a layered incommensurately modulated metal with saturated resistivity

This article reports an investigation of the new compound Sr₂Pt_8−xAs (x = 0.715), characterized by an incommensurately modulated structure and a temperature-independent electrical resistivity. The observation of saturated resistivity in this metallic system is described in the context of the Mooij correlation, which originates from the aperiodic potential of the incommensurately modulated vacancies in one of the Pt positions.

Structural characterization of free-state and product-state Mycobacterium tuberculosis me­thionyl-tRNA synthetase reveals an induced-fit ligand-recognition mechanism

Structural characterization of M. tuberculosis methionyl-tRNA synthetase provides valuable information for antibacterial drug development.

Structural flexibility of halogen bonds showed in a single-crystal-to-single-crystal [2+2] photodimerization

Single-crystal-to-single-crystal (SCSC) reactions are rare for organic solids. We describe the first example of an SCSC [2+2] photodimerization that is mediated by halogen bonding.

Exploiting superspace to clarify vacancy and Al/Si ordering in mullite

New superspace models with different modulation amplitudes indicate that any degree of ordering, from disordered to ordered, can be observed in mullite.

Identification of a tyrosine switch in copper-haem nitrite reductases

Structural characterization of the copper-haem nitrite reductase (haem CuNiR) from Ralstonia pickettii (RpNiR) revealed a tyrosine residue blocking the substrate-entry channel and binding site. The treatment of crystals with NO triggers a movement of tyrosine that allows NO- and NO₂⁻-bound species to be captured to provide the first information on ligand-bound species in this class of nitrite reductases. The use of tyrosine as a switch in activating the redox enzyme RpNiR may have wider significance as this tyrosine is found to be totally conserved in all known haem CuNiRs.

Comment on the article `Protein crystal lattices are dynamic assemblies: the role of conformational entropy in the protein condensed phase'

A comment is given on Dimova & Devedjiev [IUCrJ (2018), 5, 130–140].

Response to comment on `Protein crystal lattices are dynamic assemblies: the role of conformational entropy in the protein condensed phase'

A response is given to Nespolo's comment [IUCrJ (2018), 5, https://doi.org/10.1107/S2052252518006267] about the usage of the the term `crystal lattice' in Dimova & Devedjiev [IUCrJ (2018), 5, 130–140].

Grazing-incidence small-angle X-ray scattering (GISAXS) on small periodic targets using large beams. Erratum

An error in the article by Pflüger, Soltwisch, Probst, Scholze & Krumrey [IUCrJ (2017), 431–438] is corrected.