Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation

The most important chemical cleaning agent of the atmosphere is the hydroxyl radical, OH. It determines the oxidizing power of the atmosphere, and thereby controls the removal of nearly all gaseous atmospheric pollutants. The atmospheric supply of OH is limited, however, and could be overcome by consumption due to increasing pollution and climate change, with detrimental feedback effects. To date, the high variability of OH concentrations has prevented the use of local observations to monitor possible trends in the concentration of this species. Here we present and analyse long-term measurements of atmospheric OH concentrations, which were taken between 1999 and 2003 at the Meteorological Observatory Hohenpeissenberg in southern Germany. We find that the concentration of OH can be described by a surprisingly linear dependence on solar ultraviolet radiation throughout the measurement period, despite the fact that OH concentrations are influenced by thousands of reactants. A detailed numerical model of atmospheric reactions and measured trace gas concentrations indicates that the observed correlation results from compensations between individual processes affecting OH, but that a full understanding of these interactions may not be possible on the basis of our current knowledge of atmospheric chemistry. As a consequence of the stable relationship between OH concentrations and ultraviolet radiation that we observe, we infer that there is no long-term trend in the level of OH in the Hohenpeissenberg data set.     

Movement of 'gating charge' is coupled to ligand binding in a G-protein-coupled receptor

Activation by agonist binding of G-protein-coupled receptors (GPCRs) controls most signal transduction processes. Although these receptors span the cell membrane, they are not considered to be voltage sensitive. Recently it was shown that both the activity of GPCRs and their affinity towards agonists are regulated by membrane potential. However, it remains unclear whether GPCRs intrinsically respond to changes in membrane potential. Here we show that two prototypical GPCRs, the m2 and m1 muscarinic receptors (m2R and m1R), display charge-movement-associated currents analogous to 'gating currents' of voltage-gated channels. The gating charge-voltage relationship of m2R correlates well with the voltage dependence of the affinity of the receptor for acetylcholine. The loop that couples m2R and m1R to their G protein has a crucial function in coupling voltage sensing to agonist-binding affinity. Our data strongly indicate that GPCRs serve as sensors for both transmembrane potential and external chemical signals.     

Protein flexibility acclimatizes photosynthetic energy conversion to the ambient temperature

Adjustment of catalytic activity in response to diverse ambient temperatures is fundamental to life on Earth. A crucial example of this is photosynthesis, where solar energy is converted into electrochemical potential that drives oxygen and biomass generation at temperatures ranging from those of frigid Antarctica to those of scalding hot springs. The energy conversion proceeds by concerted mobilization of electrons and protons on photoexcitation of reaction centre protein complexes. Following physicochemical paradigms, the rates of imperative steps in this process were predicted to increase exponentially with rising temperatures, resulting in different yields of solar energy conversion at the distinct growth temperatures of photosynthetic mesophiles and extremophiles. In contrast, here we show a meticulous adjustment of energy conversion rate, resulting in similar yields from mesophiles and thermophiles. The key molecular players in the temperature adjustment process consist of a cluster of hitherto unrecognized protein cavities and an adjacent packing motif that jointly impart local flexibility crucial to the reaction centre proteins. Mutations within the packing motif of mesophiles that increase the bulkiness of the amino-acid side chains, and thus reduce the size of the cavities, promote thermophilic behaviour. This novel biomechanical mechanism accounts for the slowing of the catalytic reaction above physiological temperatures in contradiction to the classical Arrhenius paradigm. The mechanism provides new guidelines for manipulating the acclimatization of enzymes to the ambient temperatures of diverse habitats. More generally, it reveals novel protein elements that are of potential significance for modulating structure-activity relationships in membrane and globular proteins alike.     

Corneal avascularity is due to soluble VEGF receptor-1

Corneal avascularity-the absence of blood vessels in the cornea-is required for optical clarity and optimal vision, and has led to the cornea being widely used for validating pro- and anti-angiogenic therapeutic strategies for many disorders. But the molecular underpinnings of the avascular phenotype have until now remained obscure and are all the more remarkable given the presence in the cornea of vascular endothelial growth factor (VEGF)-A, a potent stimulator of angiogenesis, and the proximity of the cornea to vascularized tissues. Here we show that the cornea expresses soluble VEGF receptor-1 (sVEGFR-1; also known as sflt-1) and that suppression of this endogenous VEGF-A trap by neutralizing antibodies, RNA interference or Cre-lox-mediated gene disruption abolishes corneal avascularity in mice. The spontaneously vascularized corneas of corn1 and Pax6+/- mice and Pax6+/- patients with aniridia are deficient in sflt-1, and recombinant sflt-1 administration restores corneal avascularity in corn1 and Pax6+/- mice. Manatees, the only known creatures uniformly to have vascularized corneas, do not express sflt-1, whereas the avascular corneas of dugongs, also members of the order Sirenia, elephants, the closest extant terrestrial phylogenetic relatives of manatees, and other marine mammals (dolphins and whales) contain sflt-1, indicating that it has a crucial, evolutionarily conserved role. The recognition that sflt-1 is essential for preserving the avascular ambit of the cornea can rationally guide its use as a platform for angiogenic modulators, supports its use in treating neovascular diseases, and might provide insight into the immunological privilege of the cornea.     

劫后重生的猪鼻果蝠

一场罕见的飓风使蒙特塞拉特岛的野生动物遭受了灭顶之灾,而随后的一场火山爆发更让这里成为了不毛之地。然而,一种叫猪鼻果蝠的蝙蝠却奇迹般地生存下来,并最终成为这片森林的救世主……     

用改进的遗传算法进行多流股换热器网络综合

建立了有分流情况下换热器网络综合的教学模型,该模型改进了文献中等温混合的不合理假设,有分流情况下的换热器网络综合问题本质上是一个混合整数非线性规划(MINLP)问题。这类问题的非凸非线性特性使得目标函数存在多个局部最优解,传统的基于梯度的搜索方法在处理这类问题时由于计算规模庞大且极易陷于局部最优解而不再适用,因此对遗传算法进行多流股换热器网络综合的方法进行了研究,最后通过例题证明了方法的有效性。