Crystal engineering in all its hues in IUCrJ

The articles in crystal engineering and structural chemistry in IUCrJ published from 2019 onwards reflect the breadth and outreach of this new and important subject.

An enzyme in disguise

The enzyme carbonic anhydrase binds its zinc ion by three histidine residues in a similar manner to the way copper is bound to nitrite reductase. This remote similarity has now been shown to be real [Andring et al. (2020). IUCrJ, 7, 287–293]. A carbonic anhydrase with two bound copper ions is also a nitrite reductase.

A unique insight into the defect structures of bicontinuous mesophases in liquid crystals and hybrid materials

Han et al. [(2020), IUCrJ, 7, 228–237] using advanced electron microscopy and crystallographic modelling rationalise the microstructure of twinning defects in order to visualize mesophase transitions and surface properties of G and D bicontinuous cubic mesostructured silica. This work furthers our understanding of how these phases originate in many natural and synthetic systems.

The early history of cryo-cooling for macromolecular crystallography

A description is given of the first protein crystals to be successfully cryo-cooled with cryo-protectants; the crystals were then exposed to intense X-rays with reduced damage. A history-of-science description is provided of cryo-procedures that are universally used today with synchrotron radiation for macromolecular crystallography.

fragHAR: towards ab initio quantum-crystallographic X-ray structure refinement for polypeptides and proteins

A method to fragment quantum-chemical calculations in Hirshfeld-atom refinement is reported, which allows accurate aspherical atom X-ray refinement of polypeptides and proteins.

Small-angle neutron scattering studies suggest the mechanism of BinAB protein internalization

This study reports a solution structural investigation of the Cqm1–BinB protein complex using `contrast-matched' small-angle neutron scattering (SANS). The SANS data clearly reveal that BinB binds to the receptor Cqm1 and alters its oligomeric status from a dimer to a monomer.

Isomorphism: `molecular similarity to crystal structure similarity' in multicomponent forms of analgesic drugs tolfenamic and mefenamic acid

Many single- and multicomponent forms of two structurally related pharmaceutical drugs, tolfenamic acid and mefenamic acid, are isostructural in nature. This observation prompted the search for hidden forms by mapping the structural landscapes of the two drugs.

Cascading transitions toward unconventional charge density wave states in the quasi-two-dimensional monophosphate tungsten bronze P₄W₁₆O₅₆

Successive transitions toward unconventional charge density wave states are shown by resistivity measurements and thermal X-ray diffraction.

Evidence for binary Smc complexes lacking kite subunits in archaea

Contrary to the general concept, the archaeal Smc-based complex appears to lack the kite subunit ScpB that is essential in the bacterial Smc–ScpAB complex that mediates chromosome organization.

3D-MiXD: 3D-printed X-ray-compatible microfluidic devices for rapid, low-consumption serial synchrotron crystallography data collection in flow

A 3D-printed, X-ray-compatible microfluidic device (3D-MiXD) has been developed and used to rapidly collect highly redundant diffraction data sets from protein microcrystals in flow using a monochromatic serial synchrotron crystallography approach.

The resolution revolution in cryoEM requires high-quality sample preparation: a rapid pipeline to a high-resolution map of yeast fatty acid synthase

Optimized protocols for protein production and purification as well as cryoEM grid preparation allow the reconstruction of a 3D map of yeast fatty acid synthase (FAS) at ∼3 Å resolution from a comparatively small number of particle images within a short time. The first complete model of yeast FAS is presented.

Crystal twinning of bicontinuous cubic structures

State-of-the-art electron crystallography when combined with geometric techniques to model curved surfaces enables an in-depth study of twinning defects in bicontinuous cubic structures.

Structural insights into conformational switching in latency-associated peptide between transforming growth factor β-1 bound and unbound states

Analysis of crystallographic, solution scattering and biochemical experiments suggests a mechanism for the sequestration of transforming growth factor β-1 by latency-associated peptide (LAP) that includes a structural change in LAP from an open to a closed conformation. This mechanism contains several potential regulatory features that are exploitable for therapeutic development.

Estimation of high-order aberrations and anisotropic magnification from cryo-EM data sets in RELION-3.1

Methods are presented that estimate symmetrical and antisymmetrical optical aberrations, as well as magnification anisotropy, in a cryo-EM data set. Considering these effects improves the resolution of the 3D reconstruction when these effects are present.

Comparing the backfilling of mesoporous titania thin films with hole conductors of different sizes sharing the same mass density

Mesoporous titania thin films backfilled with the conjugated polymer PTB7-Th or the small-molecule PhenTe-BPinPh have been studied as novel materials for hybrid photovoltaics. Together with observed structural changes due to backfilling, volumetric mass density can be excluded in determining factors that influence backfilling efficiency for solar cell applications.

Characterizing crystalline defects in single nanoparticles from angular correlations of single-shot diffracted X-rays

A novel analysis method is proposed for X-ray diffraction patterns recorded in single-shot wide-angle X-ray scattering experiments of free-flying single nanoparticles. The crystalline defects in the nanoparticles are characterized by analyzing the angular correlations between Bragg spots in the single diffraction patterns.

Structure and mechanism of copper–carbonic anhydrase II: a nitrite reductase

This work utilizes X-ray crystallography to provide mechanistic insights into how carbonic anhydrase II can act as a nitrite reductase in the presence of copper.

The structural study of mutation-induced inactivation of human muscarinic receptor M4

A new approach of rationally designing an N449R mutation was developed to lock human muscarinic receptor M4 into an inactive form, and the crystal structure of the inactive M4 in a ligand-free form was determined.

Comparing serial X-ray crystallography and microcrystal electron diffraction (MicroED) as methods for routine structure determination from small macromolecular crystals

Serial X-ray crystallography and microcrystal electron diffraction were performed using microcrystals of the enzyme cyclophilin A. The results highlight the strengths and weakness of the two complementary methods.

Disappeared supramolecular isomer reappears with perylene guest

A sixfold interpenetrated metal–organic framework (MOF) with dia topology isolated in the first attempt could not be reproduced; subsequent synthesis yielded only the double-pillared-layer MOF. However, this `disappeared supramolecular isomer' reappears in the presence of a perylene guest.

On the mechanism of solid-state phase transitions in molecular crystals – the role of cooperative motion in (quasi)racemic linear amino acids

A comparative study of 34 single-crystal-to-single-crystal phase transitions in aliphatic linear-chain amino acid crystals is applied to obtain insight into their transition mechanism.

The predictive power of data-processing statistics

Combining data-analysis statistics from crystallographic software with machine learning can predict the chances of experimental phasing success.

Structure of the MICU1–MICU2 heterodimer provides insights into the gatekeeping threshold shift

Structural analysis of the apo form of the human MICU1–MICU2 heterodimer suggests how the heterodimer sets a higher Ca²⁺ threshold than the MICU1 homodimer. This provides a framework for understanding the gatekeeping role of the MICU1–MICU2 heterodimer.