The transient receptor potential (TRP) channel TRPV4 participates in multiple biological processes, and numerous TRPV4 mutations underlie several distinct and devastating diseases. Here we present the structure of Xenopus tropicalis TRPV4 at 3.8 Å resolution by cryo-electron microscopy (cryo-EM). The ion conduction pore contains an intracellular gate formed by the inner helices, but lacks any extracellular gate in the selectivity filter, as is detected in other TRPV channels. Anomalous X-ray diffraction analyses identify a single ion-binding site in the selectivity filter, explaining non-selectivity. Structural comparison with other TRP channels and distantly related voltage-gated cation channels reveals an unprecedented, unique packing interface between the voltage sensor-like domain and the pore domain, suggesting distinct gating mechanisms. Moreover, our structure begins to provide mechanistic insights to the large set of pathogenic mutations and to offer new opportunities for drug development.

Background: Human AlkB homolog 5 (Alkbh5) is an RNA demethylase that erases m 6 A modification. Results: Crystal structures of an enzymatically active Alkbh5 construct in complex with cofactors or small molecules were determined. Conclusion: Structure and activity analyses showed that Alkbh5 strongly prefers single-stranded oligos and small molecule inhibitors. Significance: The Alkbh5 structure reveals potential for structure-based design of selective inhibitors.

Ferric uptake regulator (Fur) plays a key role in the iron homeostasis of prokaryotes, such as bacterial pathogens, but the molecular mechanisms and structural basis of Fur–DNA binding remain incompletely understood. Here, we report high-resolution structures of Magnetospirillum gryphiswaldense MSR-1 Fur in four different states: apo-Fur, holo-Fur, the Fur–feoAB1 operator complex and the Fur–Pseudomonas aeruginosa Fur box complex. Apo-Fur is a transition metal ion-independent dimer whose binding induces profound conformational changes and confers DNA-binding ability. Structural characterization, mutagenesis, biochemistry and in vivo data reveal that Fur recognizes DNA by using a combination of base readout through direct contacts in the major groove and shape readout through recognition of the minor-groove electrostatic potential by lysine. The resulting conformational plasticity enables Fur binding to diverse substrates. Our results provide insights into metal ion activation and substrate recognition by Fur that suggest pathways to engineer magnetotactic bacteria and antipathogenic drugs.

All positive-stranded RNA viruses with genomes >∼7 kb encode helicases, which generally are poorly characterized. The core of the nidovirus superfamily 1 helicase (HEL1) is associated with a unique N-terminal zinc-binding domain (ZBD) that was previously implicated in helicase regulation, genome replication and subgenomic mRNA synthesis. The high-resolution structure of the arterivirus helicase (nsp10), alone and in complex with a polynucleotide substrate, now provides first insights into the structural basis for nidovirus helicase function. A previously uncharacterized domain 1B connects HEL1 domains 1A and 2A to a long linker of ZBD, which further consists of a novel RING-like module and treble-clef zinc finger, together coordinating three Zn atoms. On substrate binding, major conformational changes were evident outside the HEL1 domains, notably in domain 1B. Structural characterization, mutagenesis and biochemistry revealed that helicase activity depends on the extensive relay of interactions between the ZBD and HEL1 domains. The arterivirus helicase structurally resembles the cellular Upf1 helicase, suggesting that nidoviruses may also use their helicases for post-transcriptional quality control of their large RNA genomes.

The plasma membrane ATP release channel pannexin 1 has been implicated in numerous physiological and pathophysiological processes associated with purinergic signaling, including cancer progression, apoptotic cell clearance, inflammation, blood pressure regulation, oocyte development, epilepsy and neuropathic pain. Here, we present nearatomic resolution structures of Xenopus tropicalis and Homo sapiens PANX1 determined by cryo-electron microscopy that reveal a heptameric channel architecture. Compatible with ATP permeation, the transmembrane pore and cytoplasmic vestibule are exceptionally wide. An extracellular tryptophan ring located at the outer pore creates a constriction site, potentially functioning as a molecular sieve that restricts the size of permeable substrates. In combination with functional characterization, this work elucidates the previously unknown architecture of pannexin channels and establishes a foundation for understanding their unique channel properties as well as for developing rational therapies..