The Escherichia coli undecaprayl-pyrophosphate synthase (UPPs) structure has been solved using the single wavelength anomalous diffraction method. The putative substrate-binding site is located near the end of the ␤A-strand with Asp-26 playing a critical catalytic role. In both subunits, an elongated hydrophobic tunnel is found, surrounded by four ␤-strands (␤A-␤B-␤D-␤C) and two helices (␣2 and ␣3) and lined at the bottom with large residues Ile-62, Leu-137, Val-105, and His-103. The product distributions formed by the use of the I62A, V105A, and H103A mutants are similar to those observed for wild-type UPPs. Catalysis by the L137A UPPs, on the other hand, results in predominantly the formation of the C 70 polymer rather than the C 55 polymer. Ala-69 and Ala-143 are located near the top of the tunnel. In contrast to the A143V reaction, the C 30 intermediate is formed to a greater extent and is longer lived in the process catalyzed by the A69L mutant. These findings suggest that the small side chain of Ala-69 is required for rapid elongation to the C 55 product, whereas the large hydrophobic side chain of Leu-137 is required to limit the elongation to the C 55 product. The roles of residues located on a flexible loop were investigated. The S71A, N74A, or R77A mutants displayed 25-200-fold decrease in k cat values. W75A showed an 8-fold increase of the FPP K m value, and 22-33-fold increases in the IPP K m values were observed for E81A and S71A. The loop may function to bridge the interaction of IPP with FPP, needed to initiate the condensation reaction and serve as a hinge to control the substrate binding and product release. Prenyltransferases catalyze consecutive condensation reactions of isopentenyl pyrophosphate (IPP)1 with allylic pyrophosphate to generate linear isoprenyl polymers. The isoprenylates undergo further modification to form a variety of isoprenoid structures including steroids, terpenes, the side chains of respiratory quinones, carotenoids, natural rubber, the glycosyl carrier lipid, and prenyl proteins (1, 2). E-and Z-type prenyltransferases synthesize trans and cis double bonds, respectively, through the condensation reactions of IPP (3). Each of the E-type enzymes catalyzes the formation of a product having a specific chain length ranging from C 10 to C 50 (4).Two conserved DDXXD motifs are observed in E-type enzymes (5-7). X-ray structural (8) and site-directed mutagenesis studies (9 -12) of farnesyl-pyrophosphate synthase (FPPs) have shown that the first aspartate-rich motif binds the allylic substrate, whereas the second DDXXD binds IPP via Mg 2ϩ . Mutagenesis studies indicate that the 5th amino acid residue (Phe-77) upstream from the first DDXXD plays a critical role in controlling the chain length of the final product formed in the reaction catalyzed by E-type geranylgeranyl-pyrophosphate synthase from archaebacterium (13). By substituting this large residue with the smaller Ser, product synthesis was shifted from the production of C 20 product to C 25 and C 30 products (14). Double (F77...

A solar-driven CO2 reduction (CO2R) cell was constructed, consisting of a tandem GaAs/InGaP/TiO2/Ni photoanode in 1.0 M KOH­(aq) (pH = 13.7) to facilitate the oxygen-evolution reaction (OER), a Pd/C nanoparticle-coated Ti mesh cathode in 2.8 M KHCO3(aq) (pH = 8.0) to perform the CO2R reaction, and a bipolar membrane to allow for steady-state operation of the catholyte and anolyte at different bulk pH values. At the operational current density of 8.5 mA cm–2, in 2.8 M KHCO3(aq), the cathode exhibited <100 mV overpotential and >94% Faradaic efficiency for the reduction of 1 atm of CO2(g) to formate. The anode exhibited a 320 ± 7 mV overpotential for the OER in 1.0 M KOH­(aq), and the bipolar membrane exhibited ∼480 mV voltage loss with minimal product crossovers and >90 and >95% selectivity for protons and hydroxide ions, respectively. The bipolar membrane facilitated coupling between two electrodes and electrolytes, one for the CO2R reaction and one for the OER, that typically operate at mutually different pH values and produced a lower total cell overvoltage than known single-electrolyte CO2R systems while exhibiting ∼10% solar-to-fuels energy-conversion efficiency.

Saccharomyces cerevisiae Hop2 and Mnd1 are abundant meiosisspecific chromosomal proteins, and mutations in the corresponding genes lead to defects in meiotic recombination and in homologous chromosome interactions during mid-prophase. Analysis of various double mutants suggests that HOP2, MND1, and DMC1 act in the same genetic pathway for the establishment of close juxtaposition between homologous meiotic chromosomes. Biochemical studies indicate that Hop2 and Mnd1 proteins form a stable heterodimer with a higher affinity for double-stranded than single-stranded DNA, and that this heterodimer stimulates the strand assimilation activity of Dmc1 in vitro. Together, the genetic and biochemical results suggest that Hop2, Mnd1, and Dmc1 are functionally interdependent during meiotic DNA recombination.

H 2 O with a resistivity of >18.2 MΩ-cm was obtained from a Millipore deionized water system. A 0.5 M potassium borate solution was prepared using a 0.5 M KOH(aq) solution made from potassium hydroxide pellets (KOH, Macron Chemicals, ACS 88%) and 1 M boric acid (H 3 BO 3 , Sigma-Aldrich, BioReagent ≥99.5%) aqueous solution, for all electrochemical measurements. Ultrapure sulfuric acid (H 2 SO 4 , J. T. Baker, ACS reagent, 95%-98%). The Ag-based conductive epoxy was obtained from SPI supplies.The bipolar membrane (fumasep® FBM) was purchased from FuMA-Tech GmbH (St.Ingbert, Germany) and was stored in 1.0 M NaCl(aq) at room temperature. Bipolar membranes were cut into 3×3 cm pieces and were thoroughly rinsed with deionized H 2 O water before use. Nafion® PFSA 117 membrane (Chemours) with a thickness of 183 µm was purchased from Dupont. Membrane was soaked in DI water for at least 4 hours and rinsed with DI water before use. Growth of III-V tandem photoabsorbersThe tandem junction device was grown commercially (Sumika Electronic Materials, Inc.) according to specifications determined by 1-D numerical simulation using Helmholtz-Zentrum Berlin's AFORS-HET software. Planar III-V layers were grown epitaxially by metal-organic chemical vapor deposition (MOCVD) on an n + -GaAs wafer that had a (100)-oriented polished surface (Si-doped, acceptor concentration of 1×10 19 cm -3 , 6" diameter). Detailed information on the cell stack, including the thickness and the dopants for the III-V layers, has been provided previously.[1] Atomic layer deposition of the protective TiO 2 layerTiO 2 films were deposited on the exposed p + -GaAs epilayer at 150 °C using an between each precursor pulse. The base pressure during the TiO 2 growth was maintained at ∼0.1 Torr. ALD-TiO 2 films with thicknesses of 62.5 nm were used to protect III-V surfaces, as well as to ensure proper current matching and thus a maximized photocurrent density under 1 Sun illumination. Deposition of electrocatalysts and ohmic contactsOhmic contact to the n + -GaAs wafer was formed using a Ge-Au eutectic (20 nm Counter electrodes were either a Pt mesh or a Ti mesh. The Ti mesh electrodes were coated by electrodeposition of CoP, as described previously. [3] To minimize leaching of Co into the catholyte, the CoP counter electrode was electrochemically conditioned in a separate home-made cell with 1.0 M H 2 SO 4 (aq) in the dark using a three-electrode configuration, prior to transferring the cathode to the water-splitting cell.This electrochemical conditioning was conducted using cyclic voltammetry with a potential window of -0.15~0.05 V vs. RHE at a scan rate of 10 mV s -1 for at least 20 cycles, to remove excess Co metal in the Co phosphide film. Preparation of electrodes for 3-electrode and 2-electrode electrochemical measurementsFor use in photoelectrochemical cells, the ohmically contacted tandem-junction wafers were cleaved into samples 0.5~1.5 cm 2 in area. High-purity Ag paint (SPI supplies) was then used to mechanically attach the ohmic contact to a coiled, ...

Dendritic spines, the actin-rich protrusions emerging from dendrites, are the locations of excitatory synapses in mammalian brains. Many molecules that regulate actin dynamics also influence the morphology and/or density of dendritic spines. Since dendritic spines are neuron-specific subcellular structures, neuron-specific proteins or signals are expected to control spinogenesis. In this report, we characterize the distribution and function of neuron-predominant cortactin-binding protein 2 (CTTNBP2) in rodents. An analysis of an Expressed Sequence Tag database revealed three splice variants of mouse CTTNBP2: short, long, and intron. Immunoblotting indicated that the short form is the dominant CTTNBP2 variant in the brain. CTTNBP2 proteins were highly concentrated at dendritic spines in cultured rat hippocampal neurons as well as in the mouse brain. Knockdown of CTTNBP2 in neurons reduced the density and size of dendritic spines. Consistent with these morphological changes, the frequencies of miniature EPSCs in CTTNBP2 knockdown neurons were lower than those in control neurons. Cortactin acts downstream of CTTNBP2 in spinogenesis, as the defects caused by CTTNBP2 knockdown were rescued by overexpression of cortactin but not expression of a CTTNBP2 mutant protein lacking the cortactin interaction. Finally, immunofluorescence staining demonstrated that, unlike cortactin, CTTNBP2 stably resided at dendritic spines even after glutamate stimulation. Fluorescence recovery after photobleaching further suggested that CTTNBP2 modulates the mobility of cortactin in neurons. CTTNBP2 may thus help to immobilize cortactin in dendritic spines and control the density of dendritic spines.

In the aqueous electrochemical reduction of CO 2 , the choice of electrolyte is responsible for the catalytic activity and selectivity, although there remains a need for more in-depth understanding of electrolyte effects and mechanisms. In this study, using both experimental and simulation approaches, we report how the buffer capacity of the electrolytes affects the kinetics and equilibrium of surface reactant species and the resulting reaction rate of CO 2 with varying partial CO 2 pressure. Electrolytes investigated include KCl (nonbuffered), KHCO 3 (buffered by bicarbonate), and phosphate-buffered electrolytes. Assuming 100% methane production, the simulation successfully explains the experimental trends in maximum CO 2 flux in KCl and KHCO 3 and also highlights the difference between KHCO 3 and phosphate in terms of pK a as well as the impact of the buffer capacity. To examine the electrolyte impact on selectivity, the model is run with a constant total current density. Using this model, several factors are elucidated, including the importance of local pH, which is not in acid/ base equilibrium, the impact of buffer identity and kinetics, and the mass-transport boundary-layer thickness. The gained understanding can help to optimize CO 2 reduction in aqueous environments.

Abstract-In this paper, a novel technique for electronic beam steering in time modulated linear array (TMLA) is proposed. The beam steering technique is realized at the first sideband by controlling the switch-on time sequences of each element in the TMLA without using phase shifters. The differential evolution (DE) algorithm is employed to improve the gain and suppress the sidelobe levels (SLLs) at both the center frequency and the first sideband, simultaneously. An S-band 8-element double-layered printed dipole linear array was used to verify the technique experimentally. Measured results are compared with numerical data, and good agreement is reported. Moreover, some simulation results on the binary phase shift keying (BPSK) modulated signals arriving from different directions received by the proposed approach are presented, which validates the application of the proposed beam steering technique.

Optical obscuration and kinetic overpotentials of patterned electrocatalyst films are investigated using a 0-dimentional load-line analysis and experimental measurements.