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A riboswitch that binds fluoride was identified recently, which is surprising because both RNA and fluoride are negatively charged; here it is shown that the fluoride ion is coordinated to three positively charged magnesium ions, which are further encased in a negatively charged shell of RNA backbone phosphates and water molecules.

Group II introns are retroelements that have invaded the genomes of many prokaryotes and eukaryotes. The structure of a self-spliced group IIC intron cocrystallized with ligated exons (the target substrate) reveals the metal ions that have a role in catalysis and the intron sequences that are important in exon recognition in group II introns.

Group II introns, which are self-splicing catalytic RNAs, catalyze splicing in two distinct steps. The crystal structure of a group II intron in the pre-catalytic state directly preceding the first splicing step reveals a sharp kink in the backbone that presents the scissile phosphate of the splice site to the active site.

Gram-negative bacteria expel toxic chemicals via tripartite efflux pumps spanning both the inner and outer membranes. A crystallographic model of this tripartite efflux complex has been unavailable because co-crystallization of different components of the system has proven to be extremely difficult. The X-ray crystal structure of CusA of the CusCBA tripartite efflux system from Escherichia coli has been reported previously, and here the X-ray crystal structure of the CusBA co-complex is reported. The structure reveals that the trimeric CusA efflux pump interacts with six CusB protein molecules at the upper half of the periplasmic domain, and the predicted structure of the trimeric CusC channel was used to develop a model of for the tripartite efflux complex.

The anaphase promoting complex (APC) is a key cell-cycle regulator that has ubiquitin-ligase activity. The first structure of a complex formed between APC subunits, that of CDC26 and APC6, provides detailed structural information of APC components and suggests how CDC26 may stabilize APC6 and other complex subunits.

Group II introns are large, self-splicing RNAs that catalyze their own excision from pre-mRNA molecules. Here the authors determine the 3.7 Å crystal structure of the group II intron in the stage immediately before the second step of splicing and present a complete model for the second step of group II intron splicing.

Twisters ribozymes are a recently discovered class of non-coding, site-specific self-cleaving RNAs. Here Ren et al. describe a crystal structure of the env22twister ribozyme, propose an ion coordination and catalytic mechanism, and contrast their findings with those of two recently reported twister structures.

AbgT family of transporters have previously been implicated in the uptake of folate catabolites but remain poorly understood. Here the authors present a structural and functional characterization of Alcanivorax borkumensisYdaH, an AbgT-type transporter, revealing a unique topology and possible function as a drug efflux pump.

The validation and analysis of X-ray crystallographic data is essential for reproducibility and the development of crystallographic methods. Here, the authors describe a repository for crystallographic datasets and demonstrate some of the ways it could serve the crystallographic community.

Type I CRISPR-Cas systems require a target-searching Cascade complex and the Cas3 degradation machine to drive prokaryotic adaptation to alien nucleic acids. Cas3 crystal structures now reveal the mechanism of concerted DNA unwinding and degradation.

CDP-alcohol phosphotransferases (CDP-APs) are critical for the biosynthesis of glycerophospholipids. Here, Clarke et al.present the first structure of an enzymatically active CDP-AP in the presence of a bound lipid substrate and propose a mechanism for substrate binding and catalysis.

Prions can adopt a transmissible β-sheet-rich conformation and also form strains with different structural and biological properties. Polymorphic crystal structures of peptides from prion- and other amyloid-forming proteins suggest the structural basis for prion strains, revealing two potential mechanisms: packing and segmental polymorphism.

S-adenosyl-L-methionine is a methyl donor in many biological reactions and in bacteria regulates gene expression through binding to the SAM riboswitch. The structure of a third class of SAM riboswitches now indicates which features of SAM the riboswitches have converged on to distinguish it from the closely related S-adenosyl-L-homocysteine.

This study determines the structure of a branched lariat RNA, providing insights into rearrangement of the intron between the two steps of RNA splicing.

Polyisoprenyl-glycosyltransferases (PI-GTs) catalyse the addition of sugar to lipid carriers, which is the first step in the production of sugar donors for glycosylation. Here Ardiccioni et al.present the structure of a bacterial PI-GT and propose a mechanistic basis for sugar transfer.

The transfer of a phosphate group from a CDP-linked donor to an acceptor alcohol is catalysed by CDP-alcohol phosphotransferases. Here, Sciara et al. report crystal structures of a CDP-alcohol phosphotransferase, define roles of conserved residues and propose a mechanism of action for this protein family.

Here, the X-ray crystal structure of TrkH is solved, a protein that mediates potassium uptake in Vibrio parahaemolyticus, a bacterium. The selectivity filter of the ion transporter is very similar to what is seen in (much simpler) potassium ion channels, but it is significantly shorter. Biochemical studies were performed to explore the molecular basis of K⁺ selectivity, and it is believed that a novel gating mechanism is involved.

A crystal structure of an RNA folding intermediate of the group II intron reveals a compact conformation that is stabilized by the sequential docking of downstream intron domains, providing new insights into RNA tertiary structure assembly.

Multidrug efflux pumps significantly contribute for bacteria resistance to antibiotics. Here the authors present the structure of Campylobacter jejuni CmeB pump combined with functional FRET assays to propose a transport mechanism where each CmeB protomers is functionally independent from the trimer.

The structure of E. coli Cascade bound to foreign target DNA is presented, revealing the basis of the relaxed Cascade PAM recognition specificity, which results from its interaction with the minor groove, and demonstrating how a wedge in Cascade forces the directional pairing of the target strand with CRISPR RNA while stabilizing the non-target displaced strand.

Gram-negative bacteria, such as Escherichia coli, use tripartite efflux complexes in the resistance-nodulation-cell division family to expel toxic compounds from the cell. The CusCBA system is responsible for removing biocidal Cu(I) and Ag(I) ions. Here, the X-ray crystal structure is reported of CusA in the absence and presence of bound Cu(I) or Ag(I). The structures reveal that the metal-binding sites are located within the cleft region of the periplasmic domain. A potential pathway for ion export is proposed.

The crystal structure of mouse SCD1 bound to fatty acid stearoyl-CoA is solved at 2.6 Å resolution; the structure reveals a novel geometry for the dimetal centre, and the acyl chain of the bound fatty acid is shown to be shielded and shaped to a particular conformation by the enzyme, providing a structural basis for the selectivity of fatty acid metabolism.