MicroED structure of the NaK ion channel reveals a Na+ partition process into the selectivity filter.

Sodium (Na+) is a ubiquitous and important inorganic salt mediating many critical biological processes such as neuronal excitation, signaling, and facilitation of various transporters. The hydration states of Na+ are proposed to play critical roles in determining the conductance and the selectivity of Na+ channels, yet they are rarely captured by conventional structural biology means. Here we use the emerging cryo-electron microscopy (cryoEM) method micro-electron diffraction (MicroED) to study the structure of a prototypical tetrameric Na+-conducting channel, NaK, to 2.5 Å resolution from nano-crystals. Two new conformations at the external site of NaK are identified, allowing us to visualize a partially hydrated Na+ ion at the entrance of the channel pore. A process of dilation coupled with Na+ movement is identified leading to valuable insights into the mechanism of ion conduction and gating. This study lays the ground work for future studies using MicroED in membrane protein biophysics

Recycled plastics as fillers in polymer cement concrete composites

How to handle the plastic waste is a big task for the modern society in environmental protection. People already focus on it, especially in PET soft drink bottles. Although PET bottle can be reclaimed, its usages are restricted due to the limitation in color and difficulty in purification. On the other side, concrete is the most common material for human beings to used [sic] in construction. Concrete has good compressive strength, but poor [sic] in flexural and tensile strengths, which limits its applications. So, scientists try to improve its properties by adding the polymer into the conventional concrete, to enhance its strengths, chemical resistance and ductility. In this study, the behaviors of the PPCC in corporation [sic] of the recycled plastics as filler, without causing any problem of color and purity, has been investigated on tensile, flexural and compressive strengths, weight reduction and weathering test. The reason to chose [sic] the unsaturated polyester polymer Portland cement concrete (UP-PPCC) is to develop a novel method to transfer the plastics waste to valuable product and to solve the problem about dumping the million tons of plastic waste. The results of experiments show that UP-PPCC system has very good adhesive ability to bind the flakes of plastics with polymer-concrete matrix and the light-weighing [sic] plastic concrete can cut down the cost of transportation

K+ Channel's Equilibrium Preference Reveals the Origin of Its Conduction Selectivity and the Inactivated State of the Selectivity Filter

K^+ channels are a class of membrane proteins that rapidly and selectively transport K^+ ions across lipid membranes. K^+ ions are concentrated inside the cell, and its efflux is responsible for the rapid repolarization during action potential. Given that K^+ channels play important roles in cell physiology, their activities are tightly controlled through a variety of features, of which high ion selectivity and gating are the two most common. The work presented in this dissertation will address two fundamental questions about them. First, what is the origin of the ion selectivity during conduction? Second, C-type inactivation is gating mechanism that takes place in the selectivity filter, and how is the C-type inactivated state of the filter differ from other functional states? Ion selectivity is achieved through a highly conserved region in the channel named the selectivity filter, which is a queue of four binding sites observed in crystal structures of all K^+ channels. These sites are selective for K^+ over another abundant Na^+ ion at equilibrium, so a model based on the equilibrium selectivity was proposed to explain the conduction selectivity in K^+ channels. A recent study showed that eliminating sites from the filter of K^+-selective channels abolished their conduction selectivity, suggesting that these channels may have lost their equilibrium selectivity. To test the hypothesis, we measured the ion binding preference of K^+ channels and non-selective mutant channels. Unexpectedly, my results demonstrated that these channels have strong K^+ selectivity at equilibrium, suggesting that the conduction selectivity is likely derived from a blocking mechanism created by interacting ions inside the filter. C-type inactivation reduces ion flow through the selectivity filter of K^+ channels following channel opening. Crystal structures of the open KcsA K^+ channel shows a constricted selectivity filter that does not permit ion conduction, which was proposed by others to be the inactivated conformation. However, recent work using a semi-synthetic channel that is unable to adopt the constricted conformation but inactivates like wild-type channels challenges this idea. I measured the equilibrium ion-binding properties of channels in three different conformations to differentiate their apparent binding affinities. My results revealed that the inactivated filter is more similar to the conductive conformation than the constricted conformation from an energetic point of view. In this dissertation, I primarily applied isothermal titration calorimetry to measure the ion equilibrium preference to the selectivity filter, because it is a mechanism-free approach to detect the states of the channel in an aqueous solution. These data provide further constraints on mechanistic models of ion selectivity and inactivation in K^+ channels, which allowed to propose that the conduction selectivity of K^+ channels derives from ion interaction in the filter and that the inactivated filter resembles the conductive filter of the KcsA K^+ channel

WORKPLACE ORGANIZATION AND HUMAN RESOURCE PRACTICES: THE RETAIL FOOD INDUSTRY

Most retail food firms adhere to traditional human resources management practices, with employees enjoying little involvement in decision-making and little participation in company financial returns. More than one tenth of non-food firms have innovative human resources systems, with much individual and group involvement in decision-making and financial returns, but only a minuscule proportion of food firms have such systems. At the other end of the spectrum, more than one-fifth of food stores and eating and drinking places (and nearly one-third of food wholesale firms) have traditional systems, as compared to only one-tenth of non-food firms. The tasks and the human resource practices typical of retail food firms are consistent with each other. Core employees in these firms perform tasks that are generally simpler and less variable than those in other industries, and the firms' human resource practices generally give workers less autonomy and incentives than those in other industries. Whether the structure and variability of tasks are the result of a particular business strategy or adoption of a certain technology is not known. Which came first, these simple tasks, the workers who perform them, or these human resource policies is similarly unknown. We arrive at these conclusions through analysis of an original data set composed of 806 Minnesota firms, including 211 food firms, which allows us to characterize the change in human resource practices since the early 1980s, and to examine differences in the organization of work across companies. Work organization and human resource practices in the retail food industry have changed substantially, although the change has been less pronounced than in most other industries.Labor and Human Capital, Marketing,

Devastating chest wall necrotizing fasciitis following pigtail catheter drainage

SummaryPigtail catheter for drainage of pleural effusion has gained popularity. Complication related to the insertion of these small-bore catheter is low. In this report, we highlight two cases with devastating necrotizing fasciitis of chest wall following pigtail catheter insertion

An Unexpected Cause of a Subcutaneous Nodule: A Case Report of Dirofilaria Infection

Humans are not natural hosts of Dirofilaria; however, pulmonary or subcutaneous infections may occur through mosquitoes transmission. Patients presenting with simple subcutaneous nodules may not seek early medical attention, and hence systemic involvement through hematogenous spread may occur. Definitive diagnosis of Dirofilaria infection is made by histopathological examinations of the infected tissues. We report a patient with an incidental diagnosis of Dirofilaria infection confirmed by histopathological findings of a subcutaneous nodule on the right thigh. The source of infection remains unknown

The contrast in suspended particle dynamics at surface and near bottom on the river-dominated northern South China Sea shelf in summer: implication on physics and biogeochemistry coupling

To understand the process-response relations among physical forcing and biogeochemical properties of suspended particles (SPs) in the river-dominated northern South China Sea shelf, a 5-day shipboard observation was conducted at a fixed location on the dispersal pathway of the Zhujiang (Pearl) River plume (ZRP) in the summer of 2016. Instrumented moorings were deployed near the sampling site to record the flow and wave fields every 10 minutes. Hydrographic properties were measured hourly to identify different water masses. Water and SPs samples at the surface (3 m) and near the bottom (3 m above the bed) were taken every 3 h for the analyses of nutrients, chlorophyll-a (Chl-a), and particulate organic matter (POM including POC, PN, and δ13CPOC). Meanwhile, the grain-size composition of SPs and seafloor sediment were also analyzed. Results showed that monsoon winds drove cold upwelling and ZRP waters at the surface. Both the upwelling and ZRP regimes contained newly produced marine phytoplankton based on low POC/Chl-a ratio (PC ratio) and enriched δ13CPOC. However, SPs in the ZRP regime were smaller (<153 µm), having denser particle bulk density, and less enriched δ13CPOC, indicating different bio-communities from the upwelling regime. EOF analysis of the surface data suggested that mixing processes and the dispersal of the ZRP regime were mainly controlled by far-field storm winds, tidal modulation, and strength of mixing. On the other hand, a bottom nepheloid layer (BNL) was observed, mainly consisting of SPs<63 μm with higher bulk density than SPs at the surface. POM in the BNL was degraded and δ13CPOC-depleted according to the PC ratio and δ13CPOC. EOF analysis of the near-bottom data indicated that the dominant physical processes influencing the biogeochemical properties of SPs in the BNL were jointly the upwelling-associated lateral transport (first order) and tide-related resuspension (second order). Our study identified the contrast between the surface and near-bottom regimes with the coupling patterns among physical forcing and physiochemical properties of SPs using good constraints on particle dynamics and particle sources