Highlights d The structure of the cardiac sodium channel reveals key functional features d The antiarrhythmic drug flecainide blocks the pore below the selectivity filter d The ion selectivity filter and inactivation gate are revealed in atomic detail d An arrhythmia mutation creates a pathogenic gating pore 2 Å in diameter

Highlights d Voltage shifting and disulfide locking capture a resting-state structure of Na V Ab d Three gating charges translocate intracellularly through transmembrane electric field d Voltage sensor couples to pore opening by an elbow connecting S4 to the S4-S5 linker d Resting-state structure supports a sliding helix mechanism of gating

Mineralisation of fibrillar collagen with biomimetic process-directing agents has enabled scientists to gain insight into the potential mechanisms involved in intrafibrillar mineralisation. Here, by using polycation- and polyanion-directed intrafibrillar mineralisation, we challenge the popular paradigm that electrostatic attraction is solely responsible for polyelectrolyte-directed intrafibrillar mineralisation. Because there is no difference when a polycationic or a polyanionic electrolyte is used to direct collagen mineralisation, we argue that additional types of long-range non-electrostatic interactions are responsible for intrafibrillar mineralisation. Molecular dynamics simulations of collagen structures in the presence of extrafibrillar polyelectrolytes show that the outward movement of ions and intrafibrillar water through the collagen surface occurs irrespective of the charges of polyelectrolytes, resulting in the experimentally verifiable contraction of the collagen structures. The need to balance electroneutrality and osmotic equilibrium simultaneously to establish Gibbs-Donnan equilibrium in a polyelectrolyte-directed mineralisation system establishes a new model for collagen intrafibrillar mineralisation that supplements existing collagen mineralisation mechanisms.

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Voltage-gated sodium (NaV) channels initiate action potentials in excitable cells, and their function is altered by potent gating-modifier toxins. The α-toxin LqhIII from the deathstalker scorpion inhibits fast inactivation of cardiac NaV1.5 channels with IC50 = 11.4 nM. Here we reveal the structure of LqhIII bound to NaV1.5 at 3.3 Å resolution by cryo-EM. LqhIII anchors on top of voltage-sensing domain IV, wedged between the S1-S2 and S3-S4 linkers, which traps the gating charges of the S4 segment in a unique intermediate-activated state stabilized by four ion-pairs. This conformational change is propagated inward to weaken binding of the fast inactivation gate and favor opening the activation gate. However, these changes do not permit Na+ permeation, revealing why LqhIII slows inactivation of NaV channels but does not open them. Our results provide important insights into the structural basis for gating-modifier toxin binding, voltage-sensor trapping, and fast inactivation of NaV channels.

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Contemporary models of intrafibrillar mineralization mechanisms are established using collagen fibrils as templates without considering the contribution from collagen-bound apatite nucleation inhibitors. However, collagen matrices destined for mineralization in vertebrates contain bound matrix proteins for intrafibrillar mineralization. Negatively charged, high–molecular weight polycarboxylic acid is cross-linked to reconstituted collagen to create a model for examining the contribution of collagen-ligand interaction to intrafibrillar mineralization. Cryogenic electron microscopy and molecular dynamics simulation show that, after cross-linking to collagen, the bound polyelectrolyte caches prenucleation cluster singlets into chain-like aggregates along the fibrillar surface to increase the pool of mineralization precursors available for intrafibrillar mineralization. Higher-quality mineralized scaffolds with better biomechanical properties are achieved compared with mineralization of unmodified scaffolds in polyelectrolyte-stabilized mineralization solution. Collagen-ligand interaction provides insights on the genesis of heterogeneously mineralized tissues and the potential causes of ectopic calcification in nonmineralized body tissues.

The detection of nanobubbles on surfaces is well established (e.g., AFM and optical microscopy methods), but currently no methods exist for the direct detection of bulk nanobubbles. Here, cryo-electron microscopy (cryo-EM) has been employed to observe bubbles in aqueous solutions for the first time. Nitrogen bubbles generated by a chemical reaction were observed in amorphous ice trapped between two carbon films. The cryo-EM images of bubbles showed the same features as predicted by theory. The fact that no bubbles were observed near an air-water interface suggests that bubbles may diffuse to the nearby air-water interface and escape. The estimate of the bubble diffusion coefficient is about 30-250 μm/s.