Single Particle Fluorescence Burst Analysis of Epsin Induced Membrane Fission

Vital cellular processes, from cell growth to synaptic transmission, rely on membrane-bounded carriers and vesicles to transport molecular cargo to and from specific intracellular compartments throughout the cell. Compartment-specific proteins are required for the final step, membrane fission, which releases the transport carrier from the intracellular compartment. The role of fission proteins, especially at intracellular locations and in non-neuronal cells, while informed by the dynamin-1 paradigm, remains to be resolved. In this study, we introduce a highly sensitive approach for the identification and analysis of membrane fission machinery, called burst analysis spectroscopy (BAS). BAS is a single particle, free-solution approach, well suited for quantitative measurements of membrane dynamics. Here, we use BAS to analyze membrane fission induced by the potent, fission-active ENTH domain of epsin. Using this method, we obtained temperature-dependent, time-resolved measurements of liposome size and concentration changes, even at sub-micromolar concentration of the epsin ENTH domain. We also uncovered, at 37°C, fission activity for the full-length epsin protein, supporting the argument that the membrane-fission activity observed with the ENTH domain represents a native function of the full-length epsin protein.     

Activation of Toll-like Receptor 4 (TLR4) Attenuates Adaptive Thermogenesis via Endoplasmic Reticulum Stress

Adaptive thermogenesis is the cellular process transforming chemical energy into heat in response to cold. A decrease in adaptive thermogenesis is a contributing factor to obesity. However, the molecular mechanisms responsible for the compromised adaptive thermogenesis in obese subjects have not yet been elucidated. In this study we hypothesized that Toll-like receptor 4 (TLR4) activation and subsequent inflammatory responses are key regulators to suppress adaptive thermogenesis. To test this hypothesis, C57BL/6 mice were either fed a palmitate-enriched high fat diet or administered with chronic low-dose LPS before cold acclimation. TLR4 stimulation by a high fat diet or LPS were both associated with reduced core body temperature and heat release. Impairment of thermogenic activation was correlated with diminished expression of brown-specific markers and mitochondrial dysfunction in subcutaneous white adipose tissue (sWAT). Defective sWAT browning was concomitant with elevated levels of endoplasmic reticulum (ER) stress and autophagy. Consistently, TLR4 activation by LPS abolished cAMP-induced up-regulation of uncoupling protein 1 (UCP1) in primary human adipocytes, which was reversed by silencing of C/EBP homologous protein (CHOP). Moreover, the inactivation of ER stress by genetic deletion of CHOP or chemical chaperone conferred a resistance to the LPS-induced suppression of adaptive thermogenesis. Collectively, our data indicate the existence of a novel signaling network that links TLR4 activation, ER stress, and mitochondrial dysfunction, thereby antagonizing thermogenic activation of sWAT. Our results also suggest that TLR4/ER stress axis activation may be a responsible mechanism for obesity-mediated defective brown adipose tissue activation.     

Evolutionary Expansion of the Amidohydrolase Superfamily in Bacteria in Response to the Synthetic Compounds Molinate and Diuron

The amidohydrolase superfamily has remarkable functional diversity, with considerable structural and functional annotation of known sequences. In microbes, the recent evolution of several members of this family to catalyze the breakdown of environmental xenobiotics is not well understood. An evolutionary transition from binuclear to mononuclear metal ion coordination at the active sites of these enzymes could produce large functional changes such as those observed in nature, but there are few clear examples available to support this hypothesis. To investigate the role of binuclear-mononuclear active-site transitions in the evolution of new function in this superfamily, we have characterized two recently evolved enzymes that catalyze the hydrolysis of the synthetic herbicides molinate (MolA) and phenylurea (PuhB). In this work, the crystal structures, mutagenesis, metal ion analysis, and enzyme kinetics of both MolA and PuhB establish that these enzymes utilize a mononuclear active site. However, bioinformatics and structural comparisons reveal that the closest putative ancestor of these enzymes had a binuclear active site, indicating that a binuclear-mononuclear transition has occurred. These proteins may represent examples of evolution modifying the characteristics of existing catalysts to satisfy new requirements, specifically, metal ion rearrangement leading to large leaps in activity that would not otherwise be possible.     

microRNAs and the evolution of complex multicellularity: identification of a large,diverse complement of microRNAs in the brown alga Ectocarpus

There is currently convincing evidence that microRNAs have evolved independently in at least six different eukaryotic lineages: animals, land plants, chlorophyte green algae, demosponges, slime molds and brown algae. MicroRNAs from different lineages are not homologous but some structural features are strongly conserved across the eukaryotic tree allowing the application of stringent criteria to identify novel microRNA loci. A large set of 63 microRNA families was identified in the brown alga Ectocarpus based on mapping of RNA-seq data and nine microRNAs were confirmed by northern blotting. The Ectocarpus microRNAs are highly diverse at the sequence level with few multi-gene families, and do not tend to occur in clusters but exhibit some highly conserved structural features such as the presence of a uracil at the first residue. No homologues of Ectocarpus microRNAs were found in other stramenopile genomes indicating that they emerged late in stramenopile evolution and are perhaps specific to the brown algae. The large number of microRNA loci in Ectocarpus is consistent with the developmental complexity of many brown algal species and supports a proposed link between the emergence and expansion of microRNA regulatory systems and the evolution of complex multicellularity.     

Serum Urate and Incident Cardiovascular Disease: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

Objective

There is controversy about whether serum urate (sUA) predicts future cardiovascular disease (CVD) independently of classical risk factors, and the age at which any prediction starts. We studied the sUA-CVD association among generally healthy adults.

Methods

CARDIA recruited 5115 black and white individuals aged 18–30 years in 1985–1986 (year-0). Fatal and nonfatal CVD events by year 27 (n = 164) were ascertained during annual contacts and classified using medical records. The association with sUA (year-0, 10, 15 and 20) was modeled using Cox proportional hazards regression, pooling over gender-specific quartiles.

Results

Mean sUA concentration was higher in men than women, but increased over time in both genders. Those with elevated sUA had worse metabolic profiles that substantially deteriorated over time. Adjusting for demographic and lifestyle factors (the minimal model), baseline sUA concentration was positively associated with incident CVD (hazard ratio (HR) per mg/dL = 1.21; 95% confidence interval: 1.05, 1.39; P = 0.005). This positive association attenuated to nonsignificance in the full model accounting simultaneously for classical CVD risk factors (HR = 1.09; 0.94, 1.27; P = 0.24). Both the minimal and full models appeared to show stronger associations (than year-0 sUA) between year-10 sUA and incident CVD (HR = 1.27 and 1.12, respectively), but sUA was not statistically significant in the full model. Despite fewer events, year-15 sUA showed a significant sUA-CVD association pattern, with minimal model association magnitude comparable to year-10, and remained significant in the full model (HR = 1.19; 1.02, 1.40; P = 0.03). Hyperuricemia at year-15 strongly predicted CVD risk (HR = 2.11; 1.34, 3.33; P = 0.001), with some attenuation in the full model (HR = 1.68; P = 0.04).

Conclusions

sUA may be an early biomarker for CVD in adults entering middle age. The prediction of CVD by sUA appeared to strengthen with aging. The potential complex relation of sUA with deterioration of a cluster of metabolic abnormalities warrants future exploration.     

Estimation of the genome size of blue-green algae from DNA renaturation rates

The molecular weight of the genomes of the blue-green algaeAnacystis nidulans andAnabaena cylindrica have been estimated as 2.27×10⁹ and 2.47×10⁹ daltons respectively from the renaturation kinetics of DNA. Thus the genomes of these organisms are similar in size to that ofEscherichia coli K-12, (2.40×10⁹ daltons) measured by the same technique. No evidence was obtained of repeated sequences in the DNA of the two blue-green algae.