Homologue structure of the SLAC1 anion channel for closing stomata in leaves

The plant SLAC1 anion channel controls turgor pressure in the aperture-defining guard cells of plant stomata, thereby regulating the exchange of water vapour and photosynthetic gases in response to environmental signals such as drought or high levels of carbon dioxide. Here we determine the crystal structure of a bacterial homologue (Haemophilus influenzae) of SLAC1 at 1.20 ? resolution, and use structure-inspired mutagenesis to analyse the conductance properties of SLAC1 channels. SLAC1 is a symmetrical trimer composed from quasi-symmetrical subunits, each having ten transmembrane helices arranged from helical hairpin pairs to form a central five-helix transmembrane pore that is gated by an extremely conserved phenylalanine residue. Conformational features indicate a mechanism for control of gating by kinase activation, and electrostatic features of the pore coupled with electrophysiological characteristics indicate that selectivity among different anions is largely a function of the energetic cost of ion dehydration.     

The Role of Financial Variables in predicting economic activity

Previous research found that the US business cycle leads the European one by a few quarters, and can therefore be useful in predicting euro area gross domestic product (GDP). In this paper we investigate whether additional predictive power can be gained by adding selected financial variables belonging to either the USA or the euro area. We use vector autoregressions (VARs) that include the US and euro area GDPs as well as growth in the Rest of the World and selected combinations of financial variables. Out‐of‐sample root mean square forecast errors (RMSEs) evidence that adding financial variables produces a slightly smaller error in forecasting US economic activity. This weak macro‐financial linkage is even weaker in the euro area, where financial indicators do not improve short‐ and medium‐term GDP forecasts even when their timely availability relative to GDP is exploited. It can be conjectured that neither US nor European financial variables help predict euro area GDP as the US GDP has already embodied this information. However, we show that the finding that financial variables have no predictive power for future activity in the euro area relates to the unconditional nature of the RMSE metric. When forecasting ability is assessed as if in real time (i.e. conditionally on the information available at the time when forecasts are made), we find that models using financial variables would have been preferred in several episodes and in particular between 1999 and 2002. Copyright 2011 John Wiley & Sons, Ltd.     

Crystal structure of a potassium ion transporter, TrkH

The TrkH/TrkG/KtrB proteins mediate K(+) uptake in bacteria and probably evolved from simple K(+) channels by multiple gene duplications or fusions. Here we present the crystal structure of a TrkH from Vibrio parahaemolyticus. TrkH is a homodimer, and each protomer contains an ion permeation pathway. A selectivity filter, similar in architecture to those of K(+) channels but significantly shorter, is lined by backbone and side-chain oxygen atoms. Functional studies showed that TrkH is selective for permeation of K(+) and Rb(+) over smaller ions such as Na(+) or Li(+). Immediately intracellular to the selectivity filter are an intramembrane loop and an arginine residue, both highly conserved, which constrict the permeation pathway. Substituting the arginine with an alanine significantly increases the rate of K(+) flux. These results reveal the molecular basis of K(+) selectivity and suggest a novel gating mechanism for this large and important family of membrane transport proteins.     

Crystal structure of a phosphorylation-coupled saccharide transporter

Saccharides have a central role in the nutrition of all living organisms. Whereas several saccharide uptake systems are shared between the different phylogenetic kingdoms, the phosphoenolpyruvate-dependent phosphotransferase system exists almost exclusively in bacteria. This multi-component system includes an integral membrane protein EIIC that transports saccharides and assists in their phosphorylation. Here we present the crystal structure of an EIIC from Bacillus cereus that transports diacetylchitobiose. The EIIC is a homodimer, with an expansive interface formed between the amino-terminal halves of the two protomers. The carboxy-terminal half of each protomer has a large binding pocket that contains a diacetylchitobiose, which is occluded from both sides of the membrane with its site of phosphorylation near the conserved His250 and Glu334 residues. The structure shows the architecture of this important class of transporters, identifies the determinants of substrate binding and phosphorylation, and provides a framework for understanding the mechanism of sugar translocation.     

Motor antagonism exposed by spatial segregation and timing of neurogenesis

Walking is a key motor behaviour of limbed animals, executed by contraction of functionally antagonistic muscle groups during swing and stance phases. Nevertheless, neuronal circuits regulating the activation of antagonistic extensor-flexor muscles remain poorly understood. Here we use monosynaptically restricted trans-synaptic viruses to elucidate premotor anatomical substrates for extensor-flexor control in mice. We observe a medio-lateral spatial segregation between extensor and flexor premotor interneurons in the dorsal spinal cord. These premotor interneuron populations are derived from common progenitor domains, but segregate by timing of neurogenesis. We find that proprioceptive sensory feedback from the periphery is targeted to medial extensor premotor populations and is required for extensor-specific connectivity profiles during development. Our findings provide evidence for a discriminating anatomical basis of antagonistic circuits at the level of premotor interneurons, and point to synaptic input and developmental ontogeny as key factors in the establishment of circuits regulating motor behavioural dichotomy.     

Voltammetric detection of nanomolar levels of hypoxanthine in the presence of copper (II) at glassy carbon electrode

Nanomolar levels of the hypoxanthine in NaOH electrolyte cantaining copper (II) can be determined by anodic stripping voltammetry at a glassy carbon electrode. In the present article hypoxanthine-Cu⁺ is shown to be adsorbed on the electrode surface in the presence of an excess of copper(II). After accumulation period, hypoxanthine-Cu⁺ was stripped from the electrode surface and the anodic current coming near to the oxidation of Cu(I) to Cu(II) was measured. A linear calibration curve in the range of 5 nmol/L-1.5 mmol/L hypoxanthine, with a detection limit of 0.5 nmol/L hypoxanthine were obtained. Supported by State Key Laboratories of Transducer Technology, Chinese Academy of Sciences Hu Shengshui: born in 1946, Associate professor