The structural basis of function and regulation of neuronal cotransporters NKCC1 and KCC2

NKCC and KCC transporters mediate coupled transport of Na++K++Cl- and K++Cl- across the plasma membrane, thus regulating cell Cl- concentration and cell volume and playing critical roles in transepithelial salt and water transport and in neuronal excitability. The function of these transporters has been intensively studied, but a mechanistic understanding has awaited structural studies of the transporters. Here, we present the cryo-electron microscopy (cryo-EM) structures of the two neuronal cation-chloride cotransporters human NKCC1 (SLC12A2) and mouse KCC2 (SLC12A5), along with computational analysis and functional characterization. These structures highlight essential residues in ion transport and allow us to propose mechanisms by which phosphorylation regulates transport activity.

A Novel View on the Role of Intracellular Tails in Surface Delivery of the Potassium-Chloride Cotransporter KCC2

A plethora of neurological disorders are associated with alterations in the expression and localization of potassium-chloride cotransporter type 2 (KCC2), making KCC2 a critical player in neuronal function and an attractive target for therapeutic treatment. The activity of KCC2 is determined primarily by the rates of its surface insertion and internalization. Currently the domains of KCC2 dictating its trafficking and endocytosis are unknown. Here, using live-cell immunolabeling and biotinylation of KCC2 proteins expressed in murine neuroblastoma N2a cells, human embryonic kidney 293 cells, or primary cultures of rat hippocampal neurons, we identified a novel role for the intracellular N and C termini in differentially regulating KCC2 surface expression. We report that the N terminus is required for KCC2 insertion into the plasma membrane, whereas the C terminus is critical for the membrane stability of KCC2. Our results provide novel insights into the structure-function role of specific KCC2 domains and open perspectives in exploring structural organization of this protein.

WNK1-regulated inhibitory phosphorylation of the KCC2 cotransporter maintains the depolarizing action of GABA in immature neurons

Activation of Cl(-)-permeable γ-aminobutyric acid type A (GABAA) receptors elicits synaptic inhibition in mature neurons but excitation in immature neurons. This developmental "switch" in the GABA function depends on a postnatal decrease in intraneuronal Cl(-) concentration mediated by KCC2, a Cl(-)-extruding K(+)-Cl(-) cotransporter. We showed that the serine-threonine kinase WNK1 [with no lysine (K)] forms a physical complex with KCC2 in the developing mouse brain. Dominant-negative mutation, genetic depletion, or chemical inhibition of WNK1 in immature neurons triggered a hyperpolarizing shift in GABA activity by enhancing KCC2-mediated Cl(-) extrusion. This increase in KCC2 activity resulted from reduced inhibitory phosphorylation of KCC2 at two C-terminal threonines, Thr(906) and Thr(1007). Phosphorylation of both Thr(906) and Thr(1007) was increased in immature versus mature neurons. Together, these data provide insight into the mechanism regulating Cl(-) homeostasis in immature neurons, and suggest that WNK1-regulated changes in KCC2 phosphorylation contribute to the developmental excitatory-to-inhibitory GABA sequence.

Genetically encoded impairment of neuronal KCC2 cotransporter function in human idiopathic generalized epilepsy

The KCC2 cotransporter establishes the low neuronal Cl(-) levels required for GABAA and glycine (Gly) receptor-mediated inhibition, and KCC2 deficiency in model organisms results in network hyperexcitability. However, no mutations in KCC2 have been documented in human disease. Here, we report two non-synonymous functional variants in human KCC2, R952H and R1049C, exhibiting clear statistical association with idiopathic generalized epilepsy (IGE). These variants reside in conserved residues in the KCC2 cytoplasmic C-terminus, exhibit significantly impaired Cl(-)-extrusion capacities resulting in less hyperpolarized Gly equilibrium potentials (EG ly), and impair KCC2 stimulatory phosphorylation at serine 940, a key regulatory site. These data describe a novel KCC2 variant significantly associated with a human disease and suggest genetically encoded impairment of KCC2 functional regulation may be a risk factor for the development of human IGE.

Observation of a charged charmoniumlike structure in e+ e- → (D* D*)± π∓ at √s = 4.26 GeV

We study the process e+ e- →(D* D*)± π∓ at a center-of-mass energy of 4.26 GeV using a 827  pb(-1) data sample obtained with the BESIII detector at the Beijing Electron Positron Collider. Based on a partial reconstruction technique, the Born cross section is measured to be (137±9±15)  pb. We observe a structure near the (D* D*)± threshold in the π∓ recoil mass spectrum, which we denote as the Zc±(4025). The measured mass and width of the structure are (4026.3±2.6±3.7)  MeV/c2 and (24.8±5.6±7.7)  MeV, respectively. Its production ratio σ(e+ e- → Zc±(4025)π∓ → (D* D*)± π∓)/σ(e+ e- → (D* D*)± π∓) is determined to be 0.65±0.09±0.06. The first uncertainties are statistical and the second are systematic.

Current view on the functional regulation of the neuronal K(+)-Cl(-) cotransporter KCC2

In the mammalian central nervous system (CNS), the inhibitory strength of chloride (Cl(-))-permeable GABAA and glycine receptors (GABAAR and GlyR) depends on the intracellular Cl(-) concentration ([Cl(-)]i). Lowering [Cl(-)]i enhances inhibition, whereas raising [Cl(-)]i facilitates neuronal activity. A neuron's basal level of [Cl(-)]i, as well as its Cl(-) extrusion capacity, is critically dependent on the activity of the electroneutral K(+)-Cl(-) cotransporter KCC2, a member of the SLC12 cation-Cl(-) cotransporter (CCC) family. KCC2 deficiency compromises neuronal migration, formation and the maturation of GABAergic and glutamatergic synaptic connections, and results in network hyperexcitability and seizure activity. Several neurological disorders including multiple epilepsy subtypes, neuropathic pain, and schizophrenia, as well as various insults such as trauma and ischemia, are associated with significant decreases in the Cl(-) extrusion capacity of KCC2 that result in increases of [Cl(-)]i and the subsequent hyperexcitability of neuronal networks. Accordingly, identifying the key upstream molecular mediators governing the functional regulation of KCC2, and modifying these signaling pathways with small molecules, might constitute a novel neurotherapeutic strategy for multiple diseases. Here, we discuss recent advances in the understanding of the mechanisms regulating KCC2 activity, and of the role these mechanisms play in neuronal Cl(-) homeostasis and GABAergic neurotransmission. As KCC2 mediates electroneutral transport, the experimental recording of its activity constitutes an important research challenge; we therefore also, provide an overview of the different methodological approaches utilized to monitor function of KCC2 in both physiological and pathological conditions.

Observation of a charged (DD*)± mass peak in e+ e- → πDD* at sqrt[s] = 4.26 GeV

We report on a study of the process e+ e- → π± (DD*)∓ at sqrt[s] = 4.26  GeV using a 525 pb(-1) data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the (DD*)∓ invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner line shape, the pole mass and width are determined to be Mpole = (3883.9±1.5(stat)±4.2(syst))  MeV/c2 and Γpole = (24.8±3.3(stat)±11.0(syst))  MeV. The mass and width of the structure, which we refer to as Zc(3885), are 2σ and 1σ, respectively, below those of the Zc(3900) → π± J/ψ peak observed by BESIII and Belle in π+ π- J/ψ final states produced at the same center-of-mass energy. The angular distribution of the πZc(3885) system favors a JP = 1+ quantum number assignment for the structure and disfavors 1- or 0-. The Born cross section times the DD* branching fraction of the Zc(3885) is measured to be σ(e+ e- → π± Zc(3885)∓)×B(Zc(3885)∓ → (DD*)∓) = (83.5±6.6(stat)±22.0(syst))   pb. Assuming the Zc(3885) → DD* signal reported here and the Zc(3900) → πJ/ψ signal are from the same source, the partial width ratio (Γ(Zc(3885) → DD*)/Γ(Zc(3900) → πJ/ψ)) = 6.2±1.1(stat)±2.7(syst) is determined.

Observation of a charged charmoniumlike structure Zc(4020) and search for the Zc(3900) in e+e-→π+π-hc

We study e+e-→π+π-hc at center-of-mass energies from 3.90 to 4.42 GeV by using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections are measured at 13 energies and are found to be of the same order of magnitude as those of e+e-→π+π-J/ψ but with a different line shape. In the π±hc mass spectrum, a distinct structure, referred to as Zc(4020), is observed at 4.02  GeV/c2. The Zc(4020) carries an electric charge and couples to charmonium. A fit to the π±hc invariant mass spectrum, neglecting possible interferences, results in a mass of (4022.9±0.8±2.7)  MeV/c2 and a width of (7.9±2.7±2.6)  MeV for the Zc(4020), where the first errors are statistical and the second systematic. The difference between the parameters of this structure and the Zc(4025) observed in the D*D[over ¯]* final state is within 1.5σ, but whether they are the same state needs further investigation. No significant Zc(3900) signal is observed, and upper limits on the Zc(3900) production cross sections in π±hc at center-of-mass energies of 4.23 and 4.26 GeV are set.

Observation of a charged charmoniumlike structure in e+ e- → π+ π- J/ψ at sqrt[s] = 4.26 GeV

We study the process ee+ e- → π+ π- J/ψ at a center-of-mass energy of 4.260 GeV using a 525  pb(-1) data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be (62.9±1.9±3.7)  pb, consistent with the production of the Y(4260). We observe a structure at around 3.9  GeV/c2 in the π(±)J/ψ mass spectrum, which we refer to as the Z(c)(3900). If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the π(±)J/ψ invariant mass spectrum, neglecting interference, results in a mass of (3899.0±3.6±4.9)  MeV/c2 and a width of (46±10±20)  MeV. Its production ratio is measured to be R = (σ(e+ e- → π(±)Z(c)(3900)(∓) → π+ π- J/ψ)/σ(e+ e- → π+ π- J/ψ)) = (21.5±3.3±7.5)%. In all measurements the first errors are statistical and the second are systematic.

Improved method for efficient imaging of intracellular Cl(-) with Cl-Sensor using conventional fluorescence setup

Chloride (Cl⁻) homeostasis is known to be fundamental for central nervous system functioning. Alterations in intracellular Cl⁻ concentration ([Cl⁻]_i) and changes in the efficacy of Cl⁻ extrusion are involved in numerous neurological disorders. Therefore, there is a strong need for studies of the dynamics of [Cl⁻]_i in different cell types under physiological conditions and during pathology. Several previous works reported having successfully achieved recording of [Cl⁻]_i using genetically encoded Cl-Sensor that is composed of the cyan fluorescent protein (CFP) and Cl⁻-sensitive mutant of the yellow fluorescent protein (YFP_Cl). However, all reported works were performed using specially designed setups with ultra-sensitive CCD cameras. Our multiple attempts to monitor Cl⁻-dependent fluorescence of Cl-Sensor using conventional epifluorescence microscopes did not yield successful results. In the present work, we have analysed the reason of our failures and found that they were caused by a strong inactivation of the YFP_Cl component of Cl-Sensor during excitation of the CFP with 430 nm light. Based on the obtained results, we reduced 20-fold the intensity of the 430 nm excitation and modified the recording protocol that allows now stable long-lasting ratiometric measurements of Cl-Sensor fluorescence in different cell types including cultured hippocampal neurons and their tiny dendrites and spines. Simultaneous imaging and patch clamp recording revealed that in mature neurons, the novel protocol allows detection of as little as 2 mM changes of [Cl⁻]_i from the resting level of 5–10 mM. We demonstrate also a usefulness of the developed [Cl⁻]_i measurement procedure for large scale screening of the activity of exogenously expressed potassium-chloride co-transporter KCC2, a major neuronal Cl⁻ extruder that is implicated in numerous neurological disorders and is a target for novel therapeutical treatments.

Contact angle measurements with liquids consisting of bulky molecules

Well-measured contact angles with different solid-liquid systems fall approximately on smooth patterns when plotted versus liquid surface tension. However, there are deviations of 1 degrees -3 degrees , which are outside the error limits. It is the purpose of this paper to elucidate the reasons for such deviations. Two types of liquids were selected for advancing contact angle measurements on Teflon AF 1600 coated surfaces: a series of n-alkanes ranging from n-hexane to n-hexadecane and five liquids consisting of bulky molecules, octamethylcyclotetrasiloxane (OMCTS), methyl salicylate, tetralin, cis-decalin, and octamethyltrisiloxane (OMTS). It was found that contact angles of the liquids with bulky molecules fall on a perfectly smooth curve corresponding to a solid surface tension of 13.64 +/- 0.1 mJ/m2. However, contact angles of n-alkanes deviated from this curve by up to 3 degrees in a complicated fashion. The observed trend suggests that more than one mechanism is responsible for the deviations. Substrate-induced rearrangement of liquid molecules in the close vicinity of the surface in the case of long-chain n-alkanes and adsorption of vapor onto the solid surface in the case of short-chain n-alkanes are the most likely explanations. The results suggest that liquids with bulky molecules appear to be suitable for contact angle measurements to characterize energetics of polymeric surfaces.

Structure Investigations of Molecular Crystals Containing the Ring System Cyclo-tris(2,6-pyridylformamidine) by Means of X-ray Powder Diffraction and Force-Field-Constrained Rietveld Refinement

A new heterocyclic compound, cyclo-tris(2,6-pyridylformamidine), was synthesized as a highly crystalline powder-like substance from which very small whiskers were produced by a sublimation technique. By rotating-crystal and powder diffraction measurements, a set of structural data were obtained which were fitted mathematically to a structural model. The fitting procedure included geometry optimization byab initiocalculations, crystal structure and X-ray diffraction pattern simulation as well as structure refinement based on the newly developed Rietveld algorithmBGMN®under force-field constraints. A single-crystal structure refinement could not be carried out because of the small size of the whiskers. In order to obtain the atomic coordinates a new procedure incorporating a powder diffraction pattern refinement was used. Cyclo-tris(2,6-pyridylformamidine) crystallizes in a monoclinic unit cell witha = 28.18 (1),b = 14.67 (1),c = 4.428 (1) Å, β = 90.10 (2)°. The symmetry was determined asP21/a. The expected threefold symmetry of the cyclic compound was disturbed in the crystallized state, in agreement with solid-state NMR investigations. The best approximation was obtained when water molecules were additionally packed into the unit cell.

[A rare manifestation of Echinococcus cysticus in CT and magnetic resonance tomography]

A case of primary spinal echinococcus with bone destruction is presented and the findings in CT and MR imaging are discussed. Although CT and MRI are complementary studies for the diagnosis of the spinal echinococcosis, MRI is the study of choice for prolonged follow-up of complicated cases.

CHEMISTRY OF TETRAHYDROFURANONE DERIVATIVES: II. A CONVENIENT PROCEDURE FOR THE SYNTHESIS OF 3-ALKYL-SUBSTITUTED FURANS

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A SYNTHESIS OF 2,2,4-TRIMETHYL-4-HYDROXYTETRAHYDROFURAN, A PRODUCT OF THE PHOTOLYSIS OF 4-METHYL-4-METHOXY-2-PENTANONE

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