March 2021 issue
What is `structure' in the context of a molecular solid?
The new approach of Dittrich [IUCrJ (2021). 8, 305–318] towards describing, understanding and modelling disorders is discussed.
An algorithmic strategy to design stoichiometric quaternary and solid-solution quinary solids is described. The strategy involves recognition of structural inequivalences to generate ternary and quaternary cocrystals which can then be extended to five-component solid solutions through matching of suitable interactions.
The BCL6 BTB domain has been adapted to form a promiscuous assembly block as a basis for affinity-capture crystallography.
The interference of solute self-assembly caused by the interactions between pimelic acid and a series of homologous additives is closely related to the ability to induce the form II compound with similar packing but a different conformation to that of form I. The novel use of additives demonstrates the direct link between solute aggregation in solution and molecular conformation in crystals.
The structural analysis of mature streptavidin C1 from S. cinnamonensis is reported.
Stoichiometric ternary and quaternary, and nonstoichiometric quinary molecular solids were engineered based on structural inequivalence and combinatorial approaches from 2-nitroresorcinol. A total of 32 binary, ternary, quaternary and quinary solids were characterized. The great difficulty in obtaining such solids is that crystallization must occur in a single step from precursors in solution, with multistep sequences, as are typical in solution syntheses, not being possible in most situations.
Controlled devitrification of vitreous samples for high-resolution single-particle cryo-EM reduces beam-induced motion in the critical early frames of a movie stack by a factor of approximately four.
Competitive cocrystallization provides a green chemical method for flavonoid separation with fewer steps and lower energy consumption than the traditional organic solvent extraction method.
The crystal structure of nitrosonium nitrate (NO+NO3−) is determined by synchrotron single-crystal X-ray diffraction at pressures of 7.0 and 37.0 GPa – resolving a long-standing controversy. Remarkably, the oxygen atom of the NO+ unit is determined to be positively charged, a rare occurrence when in the presence of a less-electronegative element.
The impact of tetragonal crystal symmetry on the two-dimensional (2D) confined polymer nanostructure is demonstrated. Our research shows that this chain packing defect in the tetragonal cell can be controlled to develop along the rod long axis in 2D confinement.
A method is introduced to deconvolve SAXS datasets from evolving mixtures, such as those produced by time-resolved, temperature jump, ligand titration and chromatography-coupled setups. The method incorporates general restraints using regularized alternating least squares (REGALS), enabling physically meaningful deconvolution without the need for a hard physicochemical or structural model.
Over 100 models of SARS-CoV-2 3CLpro, a major drug-design target for COVID-19, have been carefully validated and assembled in a dedicated database. Their comparative analysis provides lessons for similar medically oriented efforts and for structural biology in general.
The whole pair distribution function modeling method is introduced to overcome the distinction between Bragg and Debye theories in analysis of powder-scattering data. Models based on Bragg's law are used to facilitate the computation of a whole pair distribution function followed by the solution of the Debye scattering equation.
Using a theoretical method which employs equilibration between the cohesive and destructive energies of a crystal, it is shown that protein layers of monomolecular thickness formed in pores can grow into macroscopic crystals. Experimental studies, stimulated from theoretical considerations, widen the palette of porous materials that can promote protein crystallization.
The first structures of the Drosophila germline-specific thioredoxins Deadhead (Dhd) and thioredoxin T (TrxT), which present unusual properties with respect to canonical Trxs, are reported. Dhd is highly positively charged, which facilitates nonspecific DNA binding to promote chromatin remodeling. TrxT contains a C-terminal extension, which is mostly unstructured and highly flexible, that modulates the redox activity of the protein. These structures will facilitate the virtual screening of small-molecule ligands and protein partners.
The experimental electron-density distribution in a titanium peroxo complex has been studied and compared with theoretical results.
Restraints extracted from molecule-in-cluster optimizations of separate disorder components permit improved least-squares modelling of experimental crystal structures, and considering energy barriers alongside enthalpy differences further enables the distinguishing of disorder into static and dynamic.
A large enhancement (118%) of electric field-induced strain of KTa1−xNbxO3 is achieved by Mn doping. The intensified local heterogeneity and modified structural features yielded by Mn dopants are demonstrated to be responsible for improved piezoelectricity. The role of Mn doping in local structures and properties of KTa1−xNbxO3 crystals is revealed, providing a basis for material design and performance optimization.
letters to the editor
The paper discusses a recent paper [Andring et al. (2020). IUCrJ, 7, 287–293] on the nitrite reductase and nitrous anhydrase activity of carbonic anhydrase.
addenda and errata
Corrigendum to the article by Andring et al. [IUCrJ, (2020), 7, 287–293].