The Preprotein Binding Domain of SecA Displays Intrinsic Rotational Dynamics

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Percutaneous treatment of spontaneous left main coronary artery dissection using drug-eluting stent

Background

Previous studies indicated that the clustering of major cardiovascular disease (CVD) risk factors is common, and multiple unhealthy lifestyles are responsible for the clustering of CVD risk factors. However, little is known about the direct association between the volume load and the clustering of CVD risk factors in general population.

Methods

We investigated the association of the clustering of CVD risk factors (defined as two or more of the following factors: hypertension, diabetes, dyslipidemia and overweight) with volume load, which was evaluated by bioelectrical impedance analysis. Hypovolaemia was defined as extracellular water/total body water (ECW/TBW) at and under the 10th percentile for the normal population.

Results

Among the 7900 adults, only 29.3% were free of any pre-defined CVD risk factors and 40.8% had clustering of CVD risk factors. Hypovolaemia in clustering group was statistically higher than that either in the single or in the none risk factor group, which was 23.7% vs. 17.0% and 10.0%, respectively (P <0.001). As a categorical outcome, the percentage of the lowest quartiles of ECW/TBW and TBW/TBWwatson in clustering group were statistically higher than either those in the single or in the none risk factor group, which were 44.9% vs. 36.9% and 25.1% (P <0.001), 36.2% vs. 32.2% and 25.0%, respectively (P <0.001). After adjusting of potential confounders, hypovolaemia was significantly associated with clustering of CVD risk factors, with an OR of 1.66 (95% CI, 1.45-1.90).

Conclusions

Hypovolaemia was associated with clustering of major CVD risk factors, which further confirms the importance of lifestyle for the development of CVD.

     

Diversity of dimethylsulfide-degrading methanogens and sulfate-reducing bacteria in anoxic sediments along the Medway Estuary,UK

Methane is a powerful greenhouse gas but the microbial diversity mediating methylotrophic methanogenesis is not well-characterized. One overlooked route to methane is via the degradation of dimethylsulfide (DMS), an abundant organosulfur compound in the environment. Methanogens and sulfate-reducing bacteria (SRB) can degrade DMS in anoxic sediments depending on sulfate availability. However, we know little about the underlying microbial community and how sulfate availability affects DMS degradation in anoxic sediments. We studied DMS-dependent methane production along the salinity gradient of the Medway Estuary (UK) and characterized, for the first time, the DMS-degrading methanogens and SRB using cultivation-independent tools. DMS metabolism resulted in high methane yield (39%–42% of the theoretical methane yield) in anoxic sediments regardless of their sulfate content. Methanomethylovorans, Methanolobus and Methanococcoides were dominant methanogens in freshwater, brackish and marine incubations respectively, suggesting niche-partitioning of the methanogens likely driven by DMS amendment and sulfate concentrations. Adding DMS also led to significant changes in SRB composition and abundance in the sediments. Increases in the abundance of Sulfurimonas and SRB suggest cryptic sulfur cycling coupled to DMS degradation. Our study highlights a potentially important pathway to methane production in sediments with contrasting sulfate content and sheds light on the diversity of DMS degraders.     

Spatial co‐localisation of extreme weather events: a clear and present danger

Extreme weather events have become a dominant feature of the narrative surrounding changes in global climate with large impacts on ecosystem stability, functioning and resilience; however, understanding of their risk of co‐occurrence at the regional scale is lacking. Based on the UK Met Office’s long‐term temperature and rainfall records, we present the first evidence demonstrating significant increases in the magnitude, direction of change and spatial co‐localisation of extreme weather events since 1961. Combining this new understanding with land‐use data sets allowed us to assess the likely consequences on future agricultural production and conservation priority areas. All land‐uses are impacted by the increasing risk of at least one extreme event and conservation areas were identified as the hotspots of risk for the co‐occurrence of multiple event types. Our findings provide a basis to regionally guide land‐use optimisation, land management practices and regulatory actions preserving ecosystem services against multiple climate threats.     

A Unitary Anesthetic Binding Site at High Resolution

Propofol is the most widely used injectable general anesthetic. Its targets include ligand-gated ion channels such as the GABA_A receptor, but such receptor-channel complexes remain challenging to study at atomic resolution. Until structural biology methods advance to the point of being able to deal with systems such as the GABA_A receptor, it will be necessary to use more tractable surrogates to probe the molecular details of anesthetic recognition. We have previously shown that recognition of inhalational general anesthetics by the model protein apoferritin closely mirrors recognition by more complex and clinically relevant protein targets; here we show that apoferritin also binds propofol and related GABAergic anesthetics, and that the same binding site mediates recognition of both inhalational and injectable anesthetics. Apoferritin binding affinities for a series of propofol analogs were found to be strongly correlated with the ability to potentiate GABA responses at GABA_A receptors, validating this model system for injectable anesthetics. High resolution x-ray crystal structures reveal that, despite the presence of hydrogen bond donors and acceptors, anesthetic recognition is mediated largely by van der Waals forces and the hydrophobic effect. Molecular dynamics simulations indicate that the ligands undergo considerable fluctuations about their equilibrium positions. Finally, apoferritin displays both structural and dynamic responses to anesthetic binding, which may mimic changes elicited by anesthetics in physiologic targets like ion channels.Most general anesthetics alter the activity of ligand-gated ion channels, and electrophysiology, photolabeling, and transgenic animal experiments imply that this effect contributes to the mechanism of anesthesia (1–9). Although the molecular mechanism for this effect is not yet clear, photolabeling studies indicate that anesthetics bind within the transmembrane regions of Cys-loop ligand-gated ion channels such as the nicotinic acetylcholine and the γ-aminobutyric acid (GABA)² type A receptors (2, 9–11). Practical difficulties associated with overexpression, purification, and crystallization of ion channels have thus far stymied investigation of the structural and energetic bases underlying anesthetic recognition. However, general anesthetics also bind specifically to sites in soluble proteins, including firefly luciferase, human serum albumin (HSA), and horse spleen apoferritin (HSAF) (12–14), and x-ray crystal structures have been determined for complexes of these proteins with several general anesthetics (14–16). In particular, HSAF is an attractive model for studying anesthetic-protein interactions because it has the highest affinity for anesthetics of any protein studied to date, has a unique anesthetic binding site, and is a multimer of 4-helix bundles, much like the putative anesthetic binding regions in ligand-gated channels. In addition, apoferritin is commercially available and crystallizes readily. Most importantly, however, the affinity of HSAF for a broad range of general anesthetics is highly correlated with anesthetic potency, confirming the utility and relevance of this model system (17).Ferritin is a 24-mer iron-binding protein. It sequesters free iron ions, thereby helping to maintain non-toxic levels of iron in the cell and functioning as a cellular iron reservoir (18, 19). Each subunit has a molecular mass of ∼20 kDa and adopts a 4-helix bundle fold. The 24-mer forms a hollow, roughly spherical particle with 432 symmetry. Two ferritin isoforms are found in mammals, heavy (H) and light (L), and 24-mers can contain all H chains, all L chains, or mixtures of varying stoichiometry; the biological significance of the H/L ratio is not yet clear (20).In addition to the large central cavity, the apoferritin 24-mer contains additional, smaller cavities at the dimer interfaces; these smaller cavities are of an appropriate size to accommodate anesthetics. X-ray crystallography has confirmed that this interfacial cavity is the binding site for the inhalational anesthetics halothane and isoflurane, and isothermal titration calorimetry (ITC) measurements have shown that this interfacial site has a relatively high affinity for these anesthetics (K_a values ∼10⁵ m⁻¹) (14).General anesthetics fall into at least two broad classes, inhalational and injectable. Whereas both classes of drugs can induce the amnesia, immobility, and hypnosis associated with anesthesia, molecules in the two classes differ substantially in their chemical and physical properties. Prior to this work, only one crystal structure has been available for an injectable general anesthetic complexed with a protein-propofol, bound to HSA (16). This structure revealed that the propofol binding sites on this protein do not, by and large, overlap with the binding sites for inhalational anesthetics. This raises the question of whether the two types of drug invariably bind to separate sets of targets, or whether they could possibly transduce their effects by binding to a single protein site. To address this question we assessed whether propofol binds to the apoferritin site that had been previously identified as the binding site for inhalational anesthetics. Using x-ray crystallography, calorimetry, and molecular modeling, we show that the two types of anesthetics do indeed share a common binding site. We also investigated structure-binding relationships for a homologous series of propofol-like compounds and found that, remarkably, the energetics of binding to apoferritin precisely match the compound''s abilities to potentiate GABA effects at GABA_A receptors, suggesting that similar structural and physicochemical factors mediate anesthetic recognition by both apoferritin and ligand-gated ion channels. This argues for the possibility that anesthetic binding might trigger structural and dynamic alterations in GABA_A receptors similar to those observed in apoferritin, and that these changes underlie anesthetic effects.     

Modeling of single-cell oil production under nitrogen-limited and substrate inhibition conditions

Sweet sorghum extract was used as substrate for lipid accumulation by the oleaginous fungus Mortierella isabellina in batch cultures. Various initial sugar (13–91 g/L) and nitrogen (100–785 mg/L) concentrations resulting in various C/N (43–53) ratios were tested. Oil accumulation ranged between 43% and 51% corresponding to oil production from 2.2 to 9.3 g/L. A detailed mathematical model was developed. This model is able to adequately predict biomass growth, lipid accumulation, and sugar and nitrogen consumption. The model assumes that fungus growth is inhibited at high sugar concentrations. A set of kinetic experiments was used for model kinetic parameters estimation, while another set of experiments was used for model validation. The developed model could be generalized for similar systems of lipid accumulation and become a useful tool for reactor design for biofuel production. Bioeng. 2011; 108:1049–1055. © 2010 Wiley Periodicals, Inc.