Structure of the saxiphilin:saxitoxin (STX) complex reveals a convergent molecular recognition strategy for paralytic toxins.

Dinoflagelates and cyanobacteria produce saxitoxin (STX), a lethal bis-guanidinium neurotoxin causing paralytic shellfish poisoning. A number of metazoans have soluble STX-binding proteins that may prevent STX intoxication. However, their STX molecular recognition mechanisms remain unknown. Here, we present structures of saxiphilin (Sxph), a bullfrog high-affinity STX-binding protein, alone and bound to STX. The structures reveal a novel high-affinity STX-binding site built from a "proto-pocket" on a transferrin scaffold that also bears thyroglobulin domain protease inhibitor repeats. Comparison of Sxph and voltage-gated sodium channel STX-binding sites reveals a convergent toxin recognition strategy comprising a largely rigid binding site where acidic side chains and a cation-π interaction engage STX. These studies reveal molecular rules for STX recognition, outline how a toxin-binding site can be built on a naïve scaffold, and open a path to developing protein sensors for environmental STX monitoring and new biologics for STX intoxication mitigation

Effects of perturbing forces on the orbital stability of planetary systems

We consider dynamical effects of additional perturbative forces due to the non-point mass nature of stars and planets: effects such as quadrupolar distortion and tidal friction in the systems of exo-planets. It is shown that these forces should not be neglected while modelling the dynamics of planetary systems, especially taking into account the undefined real masses of the planets due to unknown orbital inclinations and the unsatisfactory application of Keplerian fits to the radial velocity data in multiple planetary systems.Comment: 5 pages, 2 figures, accepted by ApJ Le

Energy Saving Analysis of a Solar Combi-system using Detailed Control Algorithm Modeled with Modelica

AbstractThis paper analyzes the detailed behavior and efficiency of a solar combi-system during a full year based on an existing control algorithm developed by SolisArt Company. Whereas so far simulations are usually done with a simplified control system or black box models, it may be formed conveniently by a detailed algorithm model to control all the system equipments thanks to Modelica language versatility. According to the results, reducing energy demands or increasing solar area lead to higher energy savings and high economy rate between 34 and 70% with 6 collectors. Finally, the developed model can also be used to size and optimize the key components of the system

Global dynamics and stability limits for planetary systems around HD 12661, HD 38529, HD 37124 and HD 160691

In order to distinguish between regular and chaotic planetary orbits we apply a new technique called MEGNO in a wide neighbourhood of orbital parameters determined using standard two-body Keplerian fits for HD 12661, HD 38529, HD 37124 and HD 160691 planetary systems. We show that the currently announced orbital parameters place these systems in very different situations from the point of view of dynamical stability. While HD 38529 and HD 37124 are located within large stability zones in the phase space around their determined orbits, the preliminary orbits in HD 160691 are highly unstable. The orbital parameters of the HD 12661 planets are located in a border region between stable and unstable dynamical regimes, so while its currently determined orbital parameters produce stable regular orbits, a minor change within the margin of error of just one parameter may result in a chaotic dynamical system.Comment: 12 pages, 3 figures, accepted ApJ, revised version following the referee's repor

The great ideas of biology: Exploration through experimentation in an undergraduate lab course

We developed an introductory laboratory course to provide a visceral experience that aims at getting students truly excited about scientific study of the living world. Our vehicle to do that was to focus on what Paul Nurse dubbed “the great ideas of biology” rather than an approach to biology that celebrates specific factual knowledge. To that end, we developed eight diverse experimental modules, each of which highlights a key biological concept and gives an opportunity to use theory to generate testable hypotheses, to perform high quality measurements to test those hypotheses (some of which are clearly wrong), and to perform sophisticated computational data analysis. Some modules incorporate modern microscopy and computational techniques in classic experiments, such as bacterial growth and the Luria‐Delbrück experiment, while others address current research questions using methods like optogenetics and single molecule measurements. We have offered the course eight times, and in the most recent edition of the course, we conducted pre/post‐course interviews and attitude surveys. The students, both bio and non‐bio majors alike, reported being captivated by seeing life occur across the broad range of experiments and model organisms. We observed demonstrable development of their curiosity and enthusiasm for biology. Additionally, we found that prior to the course, students had only vague notions about what it means to make quantitative biological measurements and interpret them. They completed the course with a clearer understanding of scientific inquiry in biology and the skills and confidence to actually perform and interpret measurements in living systems

Estimating metabolic rate for butadiene at steady state using a Bayesian physiologically-based pharmacokinetic model

In a study of 133 volunteer subjects, demographic, physiologic and pharmacokinetic data through exposure to 1,3-Butadiene (BD) were collected in order to estimate the percentage of BD concentration metabolized at steady state, and to determine whether this percentage varies across gender, racial, and age groups. During the 20 min of continuous exposure to 2 parts per million (ppm) of BD, five measurements of exhaled concentration were made on each subject. In the following 40 min washout period, another five measurements were collected. A Bayesian hierarchical compartmental physiologically-based pharmacokinetic model (PKPB) was used. Using prior information on the model parameters, Markov Chain Monte Carlo (MCMC) simulation was conducted to obtain posterior distributions. The overall estimate of the mean percent of BD metabolized at steady state was 12.7% (95% credible interval: 7.7–17.8%). There was no significant difference in gender with males having a mean of 13.5%, and females 12.3%. Among the racial groups, Hispanic (13.9%), White (13.0%), Asian (12.1%), and Black (10.9%), the significant difference came from the difference between Black and Hispanic with a 95% credible interval from −5.63 to −0.30%. Those older than 30 years had a mean of 12.2% versus 12.9% for the younger group; although this was not a statistically significant difference. Given a constant inhalation input of 2 ppm, at steady state, the overall mean exhaled concentrationwas estimated to be 1.75ppm (95% credible interval: 1.64–1.84).An equivalent parameter, first-order metabolic rate constant, was also estimated and found to be consistent with the percent of BD metabolized at steady state across gender, race, and age strata

Gravitational decoherence of planetary motions

We study the effect of the scattering of gravitational waves on planetary motions, say the motion of the Moon around the Earth. Though this effect has a negligible influence on dissipation, it dominates fluctuations and the associated decoherence mechanism, due to the very high effective temperature of the background of gravitational waves in our galactic environment.Comment: 6 pages, no figure, to appear in EuroPhysics Letters; needs `epl.cls