Population Shift Underlies Ca2+-induced Regulatory Transitions in the Sodium-Calcium Exchanger (NCX)

In eukaryotic Na⁺/Ca²⁺ exchangers (NCX) the Ca²⁺ binding CBD1 and CBD2 domains form a two-domain regulatory tandem (CBD12). An allosteric Ca²⁺ sensor (Ca3–Ca4 sites) is located on CBD1, whereas CBD2 contains a splice-variant segment. Recently, a Ca²⁺-driven interdomain switch has been described, albeit how it couples Ca²⁺ binding with signal propagation remains unclear. To resolve the dynamic features of Ca²⁺-induced conformational transitions we analyze here distinct splice variants and mutants of isolated CBD12 at varying temperatures by using small angle x-ray scattering (SAXS) and equilibrium ⁴⁵Ca²⁺ binding assays. The ensemble optimization method SAXS analysis demonstrates that the apo and Mg²⁺-bound forms of CBD12 are highly flexible, whereas Ca²⁺ binding to the Ca3–Ca4 sites results in a population shift of conformational landscape to more rigidified states. Population shift occurs even under conditions in which no effect of Ca²⁺ is observed on the globally derived D_max (maximal interatomic distance), although under comparable conditions a normal [Ca²⁺]-dependent allosteric regulation occurs. Low affinity sites (Ca1–Ca2) of CBD1 do not contribute to Ca²⁺-induced population shift, but the occupancy of these sites by 1 mm Mg²⁺ shifts the Ca²⁺ affinity (K_d) at the neighboring Ca3–Ca4 sites from ∼ 50 nm to ∼ 200 nm and thus, keeps the primary Ca²⁺ sensor (Ca3–Ca4 sites) within a physiological range. Thus, Ca²⁺ binding to the Ca3–Ca4 sites results in a population shift, where more constraint conformational states become highly populated at dynamic equilibrium in the absence of global conformational transitions in CBD alignment.     

Fifty years of Bird Study

Capsule Field ornithology is alive and well, and in the future can contribute much more in Britain and elsewhere.

Aims To review the progress of field ornithology in Britain in the context of Bird Study and the British Trust for Ornithology.

Methods An overview was taken of the main subject areas published in Bird Study to characterize progress over 50 years. Some quantification of data on the main bird organizations was performed.

ResultsKnowledge of status and trends of British birds has moved from the qualitative to generally well detailed quantitative over the past 50 years. Causes of distribution and changes are increasingly well understood in terms of habitat and of population processes. Behaviour and ecology have grown to be separate disciplines in their own right although birds have been major subjects of study within them. Migration studies have lagged somewhat in Britain but advanced elsewhere in recent decades. Amongst the main bird organizations, the BTO still has a growing membership, that of the RSPB has reached an astonishing level but may be nearing a plateau while the BOU's membership is clearly in decline.

Conclusions Field ornithology has made a large contribution to the environmental debate and the future is set for further integration across disciplines in answering large-scale questions. Great public interest has supported the growth of ornithology with a big switch from amateur to professional workers. There is a major challenge to exploit the value of birds in promoting interest in the environment and delivering sound facts to support the biodiversity debate elsewhere on Earth. Fifty years of history in Britain indicate what is possible.     

Modeling the circadian variability of ambulatorily monitored blood pressure by multiple-component analysis

The use of a set of new end points derived from ambulatory blood pressure monitoring (ABPM), in addition to the blood pressure (BP) values themselves, has been advocated to improve the sensitivity and specificity in diagnosing hypertension and to evaluate a person's response to treatment. An adequate estimation of rhythmic parameters depends, however, on the ability to describe properly the circadian pattern of BP variability. The purpose of this study was to identify a simple model that could characterize sufficiently well the circadian pattern of BP in normotensive healthy volunteers sampled by ambulatory monitoring. We studied 278 clinically healthy Spanish adults (184 men), 22.7±3.3 yr of age, without medical history of hypertension and mean BP from ambulatory profiles always below 135/85 mmHg for systolic/diastolic BP, who underwent sequential ABPM providing a total of 1115 series of BPs and heart rates (HRs), sampled on each occasion at 0.5h intervals for 48 h. Subjects were assessed while adhering to their usual diurnal activity and nocturnal sleep routine, without restrictions but avoiding the use of medication. The circadian rhythm in BP and HR for each subject was established by multiple-component analysis. A statistically significant 24h component is documented for 97% of the BP profiles, with a significant second (12h) harmonic documented in 65% of the profiles. Other ultradian harmonic components were significant in less than 20% of the profiles. A statistically significant increase in the coefficient of determination (percent of overall variability explained by the function fitted to the data) was only obtained after including the periods of 24 and 12 h for BP, and periods of 24, 12, and 6 h for HR in the model components. Although other ultradian components can be demonstrated as statistically significant in a small percent of subjects, a rather simple model including only the two first harmonics of the 24h period describes sufficiently well, at the specified sampling rate, the circadian pattern of BP in normotensive subjects. Departure from this model could characterize overt pathology, as recently demonstrated in the diagnosis of preeclampsia.     

水分对番茄不同叶龄叶片光合作用的影响

以番茄品种"金棚1号"为材料,采用盆栽方式,按照蒸腾蒸发量(ET)的50%、75%、100%和125%作为补充灌溉量研究了不同水分下番茄结果期叶片气体交换特性和光响应特征参数随叶龄的变化。结果表明:番茄叶片随着叶龄的增加,净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)逐渐降低,水分利用效率(WUE)呈先上升后下降趋势;叶龄为18 d和29 d的叶片最大净光合速率(Pmax)随灌溉量的增加均先增加后降低,分别在75%ET和100%ET处理达到最大值。叶龄为38 d和47 d的叶片Pmax均以125%ET处理最大。表观量子效率(α)随叶龄的增大也先升高后下降,在叶龄为38 d时最大;番茄叶片的光饱和点(LSP)随叶龄的加大而减小。不同水分处理下不同叶龄叶片的光响应特征参数为:叶片在叶龄为18 d时,Pmax为20.64—26.73μmol.m-.2s-1,α为0.0518—0.0556;叶龄为29 d时,Pmax为11.00—24.24μmol.m-.2s-1,α为0.0522—0.0594;叶龄为38 d时,Pmax为11.77—18.18μmol.m-.2s-1,α为0.0619—0.0693;叶龄为47 d时,Pmax为9.09—18.17μmol.m-.2s-1,α为0.0538—0.0606。随叶龄加大,增加补充灌溉量有利于延缓叶片光合能力的降低。气孔限制是水分影响番茄叶片光合作用的主要因素,气孔限制与非气孔限制因素是番茄叶片Pn随叶龄变化的原因。     

Unraveling Seasonality in Population Averages: An Examination of Seasonal Variation in Glucose Levels in Diabetes Patients Using a Large Population-based Data Set

It has been shown that the population average blood glucose level of diabetes patients shows seasonal variation, with higher levels in the winter than summer. However, seasonality in the population averages could be due to a tendency in the individual to seasonal variation, or alternatively due to occasional high winter readings (spiking), with different individuals showing this increase in different winters. A method was developed to rule out spiking as the dominant pattern underlying the seasonal variation in the population averages. Three years of data from three community-serving laboratories in Israel were retrieved. Diabetes patients (N?=?3243) with a blood glucose result every winter and summer over the study period were selected. For each individual, the following were calculated: seasonal average glucose for all winters and summers over the period of study (2006–2009), winter-summer difference for each adjacent winter-summer pair, and average of these five differences, an index of the degree of spikiness in the pattern of the six seasonal levels, and number of times out of five that each winter-summer difference was positive. Seasonal population averages were examined. The distribution of the individual's differences between adjacent seasons (winter minus summer) was examined and compared between subgroups. Seasonal population averages were reexamined in groups divided according to the index of the degree of spikiness in the individual's glucose pattern over the series of seasons. Seasonal population averages showed higher winter than summer levels. The overall median winter-summer difference on the individual level was 8?mg/dL (0.4?mmol/L). In 16.9% (95% confidence interval [CI]: 15.6–18.2%) of the population, all five winter-summer differences were positive versus 3.6% (95% CI: 3.0–4.2%) where all five winter-summer differences were negative. Seasonal variation in the population averages was not attenuated in the group having the lowest spikiness index; comparison of the distributions of the winter-summer differences in the high-, medium-, and low-spikiness groups showed no significant difference (p?=?.213). Therefore, seasonality in the population average blood glucose in diabetes patients is not just the result of occasional high measurements in different individuals in different winters, but presumably reflects a general periodic tendency in individuals for winter glucose levels to be higher than summer levels. (Author correspondence: anneke@clalit.org.il)     

Dynamical behaviour of a two-predator model with prey refuge

A three-component model consisting on one-prey and two-predator populations is considered with a Holling type II response function incorporating a constant proportion of prey refuge. We also consider the competition among predators for their food (prey) and shelter. The essential mathematical features of the model have been analyzed thoroughly in terms of stability and bifurcations arising in some selected situations. Threshold values for some parameters indicating the feasibility and stability conditions of some equilibria are determined. The range of significant parameters under which the system admits different types of bifurcations is investigated. Numerical illustrations are performed in order to validate the applicability of the model under consideration.     

Genes alternations with exposure time of environmental factors

A theoretical model discussing the environmental factors (EFs) effect of exposure time on genes, which leads to human diseases, is presented using multi-logistic model. The advantages and limitations of this model are discussed in terms of its usefulness for simulating genetic samples. It has been shown that EFs affect genes with the same degree both at high exposure level, low exposure time and at low exposure level, high exposure time.     

Microsecond Scale Replica Exchange Molecular Dynamic Simulation of Villin Headpiece: An Insight into the Folding Landscape

Abstract

Reaching the experimental time scale of millisecond is a grand challenge for protein folding simulations. The development of advanced Molecular Dynamics techniques like Replica Exchange Molecular Dynamics (REMD) makes it possible to reach these experimental timescales. In this study, an attempt has been made to reach the multi microsecond simulation time scale by carrying out folding simulations on a three helix bundle protein, Villin, by combining REMD and Amber United Atom model. Twenty replicas having different temperatures ranging from 295 K to 390 K were simulated for 1.5 μs each. The lowest Root Mean Square Deviation (RMSD) structure of 2.5 Å was obtained with respect to native structure (PDB code 1VII), with all the helices formed. The folding population landscapes were built using segment-wise RMSD and Principal Components as reaction coordinates. These analyses suggest the two-stage folding for Villin. The combination of REMD and Amber United Atom model may be useful to understand the folding mechanism of various fast folding proteins     

不同护坡草本植物的根系特征及对土壤渗透性的影响

为明确三峡库区植被边坡植物物种根系特征与土壤渗透性之间的关系,以裸地为对照,应用WinRHIZO(Pro.2004c)根系分析系统对香根草(Vetiveria zizanioides(Lin.) Nash)、百喜草(Paspalum notatum Flugge)、狗牙根(Cynodon dactylon (L) Pers.)和紫花苜蓿(Medicago sativa L.)等4种护坡草本的根系特征进行定量分析.结果表明:(1)紫花苜蓿和香根草的根长密度和根表面积密度显著大于狗牙根和百喜草;(2)不同草本类型和同一草本不同土层之间土壤渗透性存在较大差异,且各草本土壤渗透性随土层深度的增加而降低;相对于裸地而言,4种草本均能显著增强土壤渗透性,其土壤渗透性优劣表现为:香根草＞紫花苜蓿＞百喜草＞狗牙根;(3)土壤的初始入渗率、稳渗率、平均渗透率和渗透总量等各参数均随根长密度和根表面积密度增大而增强,且与直径介于0.5-5 mm不同径级的根系特征之间存在明显的相关性,故根系对土壤渗透性的增强作用主要归功于0.5-5 mm径级的根长密度和根表面积密度;(4)根长密度、根表面积密度对考斯加科夫入渗模型参数K和a有较大影响,随着根长密度和根表面积密度的增加,表征土壤初始入渗率的K值逐渐增大,而表征入渗能力衰减的参数a逐渐减小.     

灵空山油松种群年龄结构与动态分析

对山西灵空山自然保护区的油松（Pinus tabulaeformis）种群进行了调查,利用生存分析理论及谱分析理论,分析了油松种群径级结构和静态生命表,绘制了存活曲线,同时分析了种群数量的周期性。主要结果如下：（1）油松种群幼苗幼树个体数较多,中径级的个体数较稳定,而高径级由于种间竞争及环境因子的影响,个体数明显下降。（2）油松种群的存活曲线呈现Deevey-Ⅱ型。动态表现为前期增长,中期稳定,后期衰退。（3）油松种群波动存在小周期,但变化不大,说明油松种群发展较为稳定。