[Analysis of the Divalent Cation Blocking in Ion Channels by Crystal Structure and Molecular Dynamics Simulations].

Neural activity generates essential responses, such as thinking, memory formation, and muscle contraction. It is controlled by the well-coordinated activity of various cation-selective channels of the cell membrane. The divalent cation block plays an essential role in various tetrameric ion channels.

Voltage sensors of a Na channel dissociate from the pore domain and form inter-channel dimers in the resting state.

Understanding voltage-gated sodium (Na) channels is significant since they generate action potential. Na channels consist of a pore domain (PD) and a voltage sensor domain (VSD). All resolved Na structures in different gating states have VSDs that tightly interact with PDs; however, it is unclear whether VSDs attach to PDs during gating under physiological conditions.

The structural basis of divalent cation block in a tetrameric prokaryotic sodium channel.

Divalent cation block is observed in various tetrameric ion channels. For blocking, a divalent cation is thought to bind in the ion pathway of the channel, but such block has not yet been directly observed. So, the behaviour of these blocking divalent cations remains still uncertain.

Recognition Mechanism of a Novel Gabapentinoid Drug, Mirogabalin, for Recombinant Human αδ1, a Voltage-Gated Calcium Channel Subunit.

Mirogabalin is a novel gabapentinoid drug with a hydrophobic bicyclo substituent on the γ-aminobutyric acid moiety that targets the voltage-gated calcium channel subunit αδ1. Here, to reveal the mirogabalin recognition mechanisms of αδ1, we present structures of recombinant human αδ1 with and without mirogabalin analyzed by cryo-electron microscopy. These structures show the binding of mirogabalin to the previously reported gabapentinoid binding site, which is the extracellular dCache_1 domain containing a conserved amino acid binding motif.

The insights into calcium ion selectivity provided by ancestral prokaryotic ion channels.

Prokaryotic channels play an important role in the structural biology of ion channels. At the end of the 20 century, the first structure of a prokaryotic ion channel was revealed. Subsequently, the reporting of structures of various prokaryotic ion channels have provided fundamental insights into the structure of ion channels of higher organisms.

Gastric proton pump with two occluded K engineered with sodium pump-mimetic mutations.

The gastric H,K-ATPase mediates electroneutral exchange of 1H/1K per ATP hydrolysed across the membrane. Previous structural analysis of the K-occluded E2-P transition state of H,K-ATPase showed a single bound K at cation-binding site II, in marked contrast to the two K ions occluded at sites I and II of the closely-related Na,K-ATPase which mediates electrogenic 3Na/2K translocation across the membrane. The molecular basis of the different K stoichiometry between these K-counter-transporting pumps is elusive.

Development of Novel AKR1C3 Inhibitors as New Potential Treatment for Castration-Resistant Prostate Cancer.

Aldo-keto reductase (AKR) 1C3 catalyzes the synthesis of active androgens that promote the progression of prostate cancer. AKR1C3 also contributes to androgen-independent cell proliferation and survival through the metabolism of prostaglandins and reactive aldehydes. Because of its elevation in castration-resistant prostate cancer (CRPC) tissues, AKR1C3 is a promising therapeutic target for CRPC.

Crystal structure of a human plasma membrane phospholipid flippase.

ATP11C, a member of the P4-ATPase flippase, translocates phosphatidylserine from the outer to the inner plasma membrane leaflet, and maintains the asymmetric distribution of phosphatidylserine in the living cell. We present the crystal structures of a human plasma membrane flippase, ATP11C-CDC50A complex, in a stabilized E2P conformation. The structure revealed a deep longitudinal crevice along transmembrane helices continuing from the cell surface to the phospholipid occlusion site in the middle of the membrane.

A native prokaryotic voltage-dependent calcium channel with a novel selectivity filter sequence.

Voltage-dependent Ca channels (Cavs) are indispensable for coupling action potentials with Ca signaling in living organisms. The structure of Cavs is similar to that of voltage-dependent Na channels (Navs). It is known that prokaryotic Navs can obtain Ca selectivity by negative charge mutations of the selectivity filter, but native prokaryotic Cavs had not yet been identified.

A single K-binding site in the crystal structure of the gastric proton pump.

The gastric proton pump (H,K-ATPase), a P-type ATPase responsible for gastric acidification, mediates electro-neutral exchange of H and K coupled with ATP hydrolysis, but with an as yet undetermined transport stoichiometry. Here we show crystal structures at a resolution of 2.5 Å of the pump in the E2-P transition state, in which the counter-transporting cation is occluded.

Genetic manipulation of autonomic nerve fiber innervation and activity and its effect on breast cancer progression.

The effects of autonomic innervation of tumors on tumor growth remain unclear. Here we developed a series of genetic techniques to manipulate autonomic innervation in a tumor- and fiber-type-specific manner in mice with human breast cancer xenografts and in rats with chemically induced breast tumors. Breast cancer growth and progression were accelerated following stimulation of sympathetic nerves in tumors, but were reduced following stimulation of parasympathetic nerves.

Morphologic determinant of tight junctions revealed by claudin-3 structures.

Tight junction is a cell adhesion apparatus functioning as barrier and/or channel in the paracellular spaces of epithelia. Claudin is the major component of tight junction and polymerizes to form tight junction strands with various morphologies that may correlate with their functions. Here we present the crystal structure of mammalian claudin-3 at 3.

Crystal structures of the gastric proton pump.

The gastric proton pump-the H, K-ATPase-is a P-type ATPase responsible for acidifying the gastric juice down to pH 1. This corresponds to a million-fold proton gradient across the membrane of the parietal cell, the steepest known cation gradient of any mammalian tissue. The H, K-ATPase is an important target for drugs that treat gastric acid-related diseases.

Enhancement of the thermostability of mouse claudin-3 on complex formation with the carboxyl-terminal region of Clostridium perfringens enterotoxin improves crystal quality.

Tight junctions regulate substance permeation through intercellular spaces as a physical barrier or a paracellular pathway, and play an important role in maintaining the internal environment. Claudins, which are tetraspan-transmembrane proteins, are pivotal components of tight junctions. In mammals 27 claudin subtypes have been identified, each of which interacts with specific subtypes.

Optimized expression and purification of NavAb provide the structural insight into the voltage dependence.

Voltage-gated sodium channels are crucial for electro-signalling in living systems. Analysis of the molecular mechanism requires both fine electrophysiological evaluation and high-resolution channel structures. Here, we optimized a dual expression system of NavAb, which is a well-established standard of prokaryotic voltage-gated sodium channels, for E.

Molecular determinants of prokaryotic voltage-gated sodium channels for recognition of local anesthetics.

Local anesthetics (LAs) inhibit mammalian voltage-gated Na(+) channels (Navs) and are thus clinically important. LAs also inhibit prokaryotic Navs (BacNavs), which have a simpler structure than mammalian Navs. To elucidate the detailed mechanisms of LA inhibition to BacNavs, we used NavBh, a BacNav from Bacillus halodurans, to analyze the interactions of several LAs and quaternary ammoniums (QAs).

Tight junctions. Structural insight into tight junction disassembly by Clostridium perfringens enterotoxin.

The C-terminal region of Clostridium perfringens enterotoxin (C-CPE) can bind to specific claudins, resulting in the disintegration of tight junctions (TJs) and an increase in the paracellular permeability across epithelial cell sheets. Here we present the structure of mammalian claudin-19 in complex with C-CPE at 3.7 Å resolution.

Control of Spontaneous Ca2+ Transients Is Critical for Neuronal Maturation in the Developing Neocortex.

Neural activity plays roles in the later stages of development of cortical excitatory neurons, including dendritic and axonal arborization, remodeling, and synaptogenesis. However, its role in earlier stages, such as migration and dendritogenesis, is less clear. Here we investigated roles of neural activity in the maturation of cortical neurons, using calcium imaging and expression of prokaryotic voltage-gated sodium channel, NaChBac.

Two alternative conformations of a voltage-gated sodium channel.

Activation and inactivation of voltage-gated sodium channels (Navs) are well studied, yet the molecular mechanisms governing channel gating in the membrane remain unknown. We present two conformations of a Nav from Caldalkalibacillus thermarum reconstituted into lipid bilayers in one crystal at 9Å resolution based on electron crystallography. Despite a voltage sensor arrangement identical with that in the activated form, we observed two distinct pore domain structures: a prominent form with a relatively open inner gate and a closed inner-gate conformation similar to the first prokaryotic Nav structure.

The C-terminal helical bundle of the tetrameric prokaryotic sodium channel accelerates the inactivation rate.

Most tetrameric channels have cytosolic domains to regulate their functions, including channel inactivation. Here we show that the cytosolic C-terminal region of NavSulP, a prokaryotic voltage-gated sodium channel cloned from Sulfitobacter pontiacus, accelerates channel inactivation. The crystal structure of the C-terminal region of NavSulP grafted into the C-terminus of a NaK channel revealed that the NavSulP C-terminal region forms a four-helix bundle.

Arrangement and mobility of the voltage sensor domain in prokaryotic voltage-gated sodium channels.

Prokaryotic voltage-gated sodium channels (Na(V)s) form homotetramers with each subunit contributing six transmembrane α-helices (S1-S6). Helices S5 and S6 form the ion-conducting pore, and helices S1-S4 function as the voltage sensor with helix S4 thought to be the essential element for voltage-dependent activation. Although the crystal structures have provided insight into voltage-gated K channels (K(V)s), revealing a characteristic domain arrangement in which the voltage sensor domain of one subunit is close to the pore domain of an adjacent subunit in the tetramer, the structural and functional information on Na(V)s remains limited.

Evidence for lateral mobility of voltage sensors in prokaryotic voltage-gated sodium channels.

Voltage-sensor domains (VSDs) in voltage-gated ion channels are thought to regulate the probability that a channel adopts an open conformation by moving vertically in the lipid bilayer. Here we characterized the movement of the VSDs of the prokaryotic voltage-gated sodium channel, NaChBac. Substitution of residue T110, which is located on the extracellular side of the fourth transmembrane helix of the VSD, by cysteine resulted in the formation of a disulfide bond between adjacent subunits in the channel.

Crystal structure of the Homer 1 family conserved region reveals the interaction between the EVH1 domain and own proline-rich motif.

PSD-Zip45 (also named Homer 1c/Vesl-1L) is a synaptic scaffolding protein, which interacts with neurotransmitter receptors and other scaffolding proteins to target them into post-synaptic density (PSD), a specialized protein complex at the synaptic junction. Binding of the PSD-Zip45 to the receptors and scaffolding proteins results in colocalization and clustering of its binding partners in PSD. It has an Ena/VASP homology 1 (EVH1) domain in the N terminus for receptor binding, two leucine zipper motifs in the C terminus for clustering, and a linking region whose function is unclear despite the high level of conservation within the Homer 1 family.