Energy barriers, cooperativity, and hidden intermediates in the folding of small proteins

Current theoretical views of the folding process of small proteins (< approximately 100 amino acids) postulate that the landscape of potential mean force (PMF) for the formation of the native state has a funnel shape and that the free energy barrier to folding arises from the chain configurational entropy only. However, recent theoretical studies on the formation of hydrophobic clusters with explicit water suggest that a barrier should exist on the PMF of folding, consistent with the fact that protein folding generally involves a large positive activation enthalpy at room temperature. In addition, high-resolution structural studies of the hidden partially unfolded intermediates have revealed the existence of non-native interactions, suggesting that the correction of the non-native interactions during folding should also lead to barriers on PMF. To explore the effect of a PMF barrier on the folding behavior of proteins, we modified Zwanzig's model for protein folding with an uphill landscape of PMF for the formation of transition states. We found that the modified model for short peptide segments can satisfy the thermodynamic and kinetic criteria for an apparently two-state folding. Since the Levinthal paradox can be solved by a stepwise folding of short peptide segments, a landscape of PMF with a locally uphill search for the transition state and cooperative stabilization of folding intermediates/native state is able to explain the available experimental results for small proteins. We speculate that the existence of cooperative hidden folding intermediates in small proteins could be the consequence of the highly specific structures of the native state, which are selected by evolution to perform specific functions and fold in a biologically meaningful time scale.     

Allocation of carbon in a mature eucalypt forest and some effects of soil phosphorus availability

Pools and annual fluxes of carbon (C) were estimated for a mature Eucalyptus pauciflora (snowgum) forest with and without phosphorus (P) fertilizer addition to determine the effect of soil P availability on allocation of C in the stand. Aboveground biomass was estimated from allometric equations relating stem and branch diameters of individual trees to their biomass. Biomass production was calculated from annual increments in tree diameters and measurements of litterfall. Maintenance and construction respiration were calculated for each component using equations given by Ryan (1991a). Total belowground C flux was estimated from measurements of annual soil CO₂ efflux less the C content of annual litterfall (assuming forest floor and soil C were at approximate steady state for the year that soil CO₂ efflux was measured). The total C content of the standing biomass of the unfertilized stand was 138 t ha^-1, with approximately 80% aboveground and 20% belowground. Forest floor C was 8.5 t ha^-1. Soil C content (0–1 m) was 369 t ha^-1 representing 70% of the total C pool in the ecosystem. Total gross annual C flux aboveground (biomass increment plus litterfall plus respiration) was 11.9 t ha^-1 and gross flux belowground (coarse root increment plus fine root production plus root respiration) was 5.1 t ha^-1. Total annual soil efflux was 7.1 t ha^-1, of which 2.5 t ha^-1 (35%) was contributed by litter decomposition.The short-term effect of changing the availability of P compared with C on allocation to aboveground versus belowground processes was estimated by comparing fertilized and unfertilized stands during the year after treatment. In the P-fertilized stand annual wood biomass increment increased by 30%, there was no evidence of change in canopy biomass, and belowground C allocation decreased by 19% relative to the unfertilized stand. Total annual C flux was 16.97 and 16.75 t ha^-1 yr^-1 and the ratio of below- to aboveground C allocation was 0.43 and 0.35 in the unfertilized and P-fertilized stands, respectively. Therefore, the major response of the forest stand to increased soil P availability appeared to be a shift in C allocation; with little change in total productivity. These results emphasise that both growth rate and allocation need to be estimated to predict changes in fluxes and storage of C in forests that may occur in response to disturbance or climate change.     

Gastric inhibitory polypeptide modulates adiposity and fat oxidation under diminished insulin action

Gut hormone gastric inhibitory polypeptide (GIP) stimulates insulin secretion from pancreatic β-cells upon ingestion of nutrients. Inhibition of GIP signaling prevents the onset of obesity and consequent insulin resistance induced by high-fat diet. In this study, we investigated the role of GIP in accumulation of triglycerides into adipocytes and in fat oxidation peripherally using insulin receptor substrate (IRS)-1-deficient mice and revealed that IRS-1^−/−GIPR^−/− mice exhibited both reduced adiposity and ameliorated insulin resistance. Furthermore, increased gene expression of CD36 and UCP2 in liver, and increased expression and enzyme activity of 3-hydroxyacyl-CoA dehydrogenase in skeletal muscle of IRS-1^−/−GIPR^−/− mice might contribute to the lower respiratory quotient and the higher fat oxidation in light phase. These results suggest that GIP plays a crucial role in switching from fat oxidation to fat accumulation under the diminished insulin action as a potential target for secondary prevention of insulin resistance.     

Spatiotemporal and kinematic changes in gait while carrying an energy harvesting assault pack system

Soldiers are fielded with a variety of equipment including battery powered electronic devices. An energy harvesting assault pack (EHAP) was developed to provide a power source to recharge batteries and reduce the quantity and load of extra batteries carried into the field. Little is known about the biomechanical implications of carrying a suspended-load energy harvesting system compared to the military standard assault pack (AP). Therefore, the goal of this study was to determine the impact of pack type and load magnitude on spatiotemporal and kinematic parameters while walking at 1.34 m/s on an instrumented treadmill at decline, level, and incline grades. There was greater forward trunk lean while carrying the EHAP and the heavy load (decline: p < 0.001; level: p = 0.009; incline: p = 0.003). As load increased from light to heavy, double support stance time was longer (decline: p = 0.012; level: p < 0.001; incline: p < 0.001), strides were shorter (incline: p = 0.013), and knee flexion angle at heel strike was greater (decline: p = 0.033; level: p = 0.035; incline: p = 0.005). When carrying the EHAP, strides (decline: p = 0.007) and double support stance time (incline: p = 0.006) was longer, the knee was more flexed at heel strike (level: p = 0.014; incline: p < 0.001) and there was a smaller change in knee flexion during weight acceptance (decline: p = 0.0013; level: p = 0.007; incline: p = 0.0014). Carrying the EHAP elicits changes to gait biomechanics compared to carrying the standard AP. Understanding how load-suspension systems influence loaded gait biomechanics are warranted before transitioning these systems into military or recreational environments.     

Fair Resource Allocation to Health Research: Priority Topics for Bioethics Scholarship

This article draws attention to the limited amount of scholarship on what constitutes fairness and equity in resource allocation to health research by individual funders. It identifies three key decisions of ethical significance about resource allocation that research funders make regularly and calls for prioritizing scholarship on those topics – namely, how health resources should be fairly apportioned amongst public health and health care delivery versus health research, how health research resources should be fairly allocated between health problems experienced domestically versus other health problems typically experienced by disadvantaged populations outside the funder's country, and how domestic and non‐domestic health research funding should be further apportioned to different areas, e.g. types of research and recipients. These three topics should be priorities for bioethics research because their outcomes have a substantial bearing on the achievement of health justice. The proposed agenda aims to move discussion on the ethics of health research funding beyond its current focus on the mismatch between worldwide basic and clinical research investment and the global burden of disease. Individual funders’ decision‐making on whether and to what extent to allocate resources to non‐domestic health research, health systems research, research on the social determinants of health, capacity development, and recipients in certain countries should also be the focus of ethical scrutiny.     

Simulated impact of the renewable fuels standard on US Conservation Reserve Program enrollment and conversion

A socioeconomic model is used to estimate the land‐use implications on the U.S. Conservation Reserve Program from potential increases in second‐generation biofuel production. A baseline scenario with no second‐generation biofuel production is compared to a scenario where the Renewable Fuels Standard (RFS2) volumes are met by 2022. We allow for the possibility of converting expiring CRP lands to alternative uses such as conventional crops, dedicated second‐generation biofuel crops, or harvesting existing CRP grasses for biomass. Results indicate that RFS2 volumes (RFS2‐v) can be met primarily with crop residues (78% of feedstock demand) and woody residues (19% of feedstock demand) compared with dedicated biomass (3% of feedstock demand), with only minimal conversion of cropland (0.27 million hectares, <1% of total cropland), pastureland (0.28 million hectares of pastureland, <1% of total pastureland), and CRP lands (0.29 million hectares of CRP lands, 3% of existing CRP lands) to biomass production. Meeting RFS2 volumes would reduce CRP re‐enrollment by 0.19 million hectares, or 4%, below the baseline scenario where RFS2 is not met. Yet under RFS2‐v scenario, expiring CRP lands are more likely to be converted to or maintain perennial cover, with 1.78 million hectares of CRP lands converting to hay production, and 0.29 million hectares being harvested for existing grasses. A small amount of CRP is harvested for existing biomass, but no conversion of CRP to dedicated biomass crops, such as switchgrass, are projected to occur. Although less land is enrolled in CRP under RFS2‐v scenario, total land in perennial cover increases by 0.15 million hectares, or 2%, under RFS2‐v. Sensitivity to yield, payment and residue retention assumptions are evaluated.     

三江源区不同建植期人工草地甘肃马先蒿生物量分配

以三江源区不同建植期人工草地中典型杂草甘肃马先蒿为研究对象,以建植前为对照,比较建植期为5年、10年的垂穗披碱草人工草地中马先蒿形态特征、器官生物量和资源投资状况.结果表明:(1)甘肃马先蒿在不同建植期人工草地中个体形态特征如株高、花柱高、花数目存在显著差异,而根系长、分枝数、叶片数差异不显著;不同阶段各器官生物量发生改变,根系生物量、茎叶生物量、繁殖器官生物量变化差异显著,而总生物量无显著差异.(2)综合建植前与建植后5、10年这3个时期样地中甘肃马先蒿在形态特征与资源投资状况的变化特征发现:总生物量、茎叶生物量、繁殖器官生物量、花数都呈现先下降再上升的V"字形变化趋势,根系生物量、株高逐渐增大,而花序长度则持续下降;资源相对投资比例也随建植期的不同表现出明显的差异,地上部分和地下部分的相对投资随时间的增加而上升,繁殖投资则表现出逐年降低的趋势.(3)以总生物量为个体大小参数,在同一时期内甘肃马先蒿各器官的绝对生物量具有明显的大小依赖性,随着个体大小的增加,茎叶生物量、根系生物量和花生物量均显著增加.但不同建植期人工草地中各器官生物量的个体大小依赖性响应程度不同,其中茎叶生物量和根系生物量的大小依赖程度随建植年限的增加而增加,而花生物量的个体大小依赖性却随建植期的延长而减弱.     

Growth patterns of Juncus gerardi clonal populations in a coastal habitat

Juncus gerardi populations demonstrated a logistic growth curve during the colonization stage. Shoot production by vegetative multiplication was virtually continuous from December to June. Experiments suggested that the stabilisation stage of the demographic curve reflected water deficit. Taller, fertile, winter and early spring cohorts could be distinguished from shorter, infertile end of spring and beginning of summer cohorts. Shoot emergence began in March and terminated at the end of June, when water becomes a limiting factor due to a period of water shortage, typical of the thermo-atlantic climate. Spatial extension of populations was due to rhizome growth, which ceased during flowering.Flowering in May temporarily checked growth in shoot height of all emerged cohorts. No cost of reproduction was demonstrated concerning the rate of appearance of new shoots.Although fertile shoots were taller than vegetative shoots, their growth rates were significantly lower from April onwards. The tallest fertile shoots produced the most capsules.Energy allocation to seed production is the only possible means for long-term establishment of new genotypes, and vegetative multiplication appears as the principal source of recruitment of new modules in Juncus gerardi.Resource allocation patterns in this clonal species are discussed in relation to the ecological background in the concerned marshlands and with theoretical proposals derived from models of spatial colonization strategies in clonal plants.Nomenclature: follows Flora Europaea (Tutin et al., 1964ndash;1980).     

Copper-induced alteration in sucrose partitioning and its relationship to the root growth of two Elsholtzia haichowensis Sun populations

Hydroponic culture was used to comparatively investigate the copper (Cu)-induced alteration to sucrose metabolism and biomass allocation in two Elsholtzia haichowensis Sun populations with one from a Cu-contaminated site (CS) and the other from a non-contaminated site (NCS). Experimental results revealed that biomass allocation preferred roots over shoots in CS population, and shoots over roots in NCS population under Cu exposure. The difference in biomass allocation was correlated with the difference in sucrose partitioning between the two populations. Cu treatment (45 μM) significantly decreased leaf sucrose content and increased root sucrose content in CS population as a result of the increased activities of leaf sucrose synthesis enzymes (sucrose phosphate synthetase and sucrose synthase) and root sucrose cleavage enzyme (vacuolar invertase), which led to increased sucrose transport from leaves to roots. In contrast, higher Cu treatment increased sucrose content in leaves and decreased sucrose content in roots in NCS population as a result of the decreased activities of root sucrose cleavage enzymes (vacuolar and cell wall invertases) that led to less sucrose transport from leaves to roots. These results provide important insights into carbon resource partitioning and biomass allocation strategies in metallophytes and are beneficial for the implementation of phytoremediation techniques.