Electrostatic changes in phosphorylase kinase induced by its obligatory allosteric activator Ca2+

Skeletal muscle phosphorylase kinase (PhK) is a 1.3-MDa hexadecameric complex that catalyzes the phosphorylation and activation of glycogen phosphorylase b. PhK has an absolute requirement for Ca(2+) ions, which couples the cascade activation of glycogenolysis with muscle contraction. Ca(2+) activates PhK by binding to its nondissociable calmodulin subunits; however, specific changes in the structure of the PhK complex associated with its activation by Ca(2+) have been poorly understood. We present herein the first comparative investigation of the physical characteristics of highly purified hexadecameric PhK in the absence and presence of Ca(2+) ions using a battery of biophysical probes as a function of temperature. Ca(2+)-induced differences in the tertiary and secondary structure of PhK measured by fluorescence, UV absorption, FTIR, and CD spectroscopies as low resolution probes of PhK's structure were subtle. In contrast, the surface electrostatic properties of solvent accessible charged and polar groups were altered upon the binding of Ca(2+) ions to PhK, which substantially affected both its diffusion rate and electrophoretic mobility, as measured by dynamic light scattering and zeta potential analyses, respectively. Overall, the observed physicochemical effects of Ca(2+) binding to PhK were numerous, including a decrease in its electrostatic surface charge that reduced particle mobility without inducing a large alteration in secondary structure content or hydrophobic tertiary interactions. Without exception, for all analyses in which the temperature was varied, the presence of Ca(2+) rendered the enzyme increasingly labile to thermal perturbation.     

N-terminal deletion affects catalytic activity of saporin toxin

Single-chain ribosome inactivating proteins (RIPs) are cytotoxic components of macromolecular pharmaceutics for immunotherapy of cancer and other human diseases. Saporin belongs to a family of single-chain RIPs sharing sequence and structure homology. In a preliminary attempt to define an active saporin polypeptide of minimum size we have generated proteins with deletions at the N-terminus and at the C-terminus. An N-terminal (sapDelta1-20) deletion mutant of saporin displayed defective catalytic activity, drastically reduced cytotoxicity but increased ability to interact with liposomes inducing their permeabilization at low pH. A C-terminal (sapDelta239-253) deletion mutant showed instead a moderate reduction in cytotoxic activity. A substantial alteration of secondary structure was evidenced by Fourier transformed infrared spectroscopy (FTIR) in the sapDelta1-20 mutant. It can be hypothesized that the defective functions of sapDelta1-20 are due to alterations of its spatial configuration.     

Secondary chemicals protect mould from fungivory

The vast repertoire of toxic fungal secondary metabolites has long been assumed to have an evolved protective role against fungivory. It still remains elusive, however, whether fungi contain these compounds as an anti-predator adaptation. We demonstrate that loss of secondary metabolites in the soil mould Aspergillus nidulans causes, under the attack of the fungivorous springtail Folsomia candida, a disadvantage to the fungus. Springtails exhibited a distinct preference for feeding on a mutant deleted for LaeA, a global regulator of Aspergillus secondary metabolites. Consumption of the mutant yielded a reproductive advantage to the arthropod but detrimental effects on fungal biomass compared with a wild-type fungus capable of producing the entire arsenal of secondary metabolites. Our results demonstrate that fungal secondary metabolites shape food choice behaviour, can affect population dynamics of fungivores, and suggest that fungivores may provide a selective force favouring secondary metabolites synthesis in fungi.     

Effects of plant extracts on the feeding behaviour of the slug Arion lusitanicus

Methanol extracts of the plants Geranium robertianum, Lepidium sativum, Origanum vulgare, Salvia officinalis, Salvia pratensis, Saponaha officinalis, Thymus vulgaris, Trifolium repens and Valerianella locusta were produced and applied to cotyledons of 6–8 days old rape seedlings to investigate whether they can influence the feeding of the slug Arion lusitanicus on young rape. All plant extracts appeared to reduce slug feeding on rape to some extent, but only the extracts of Saponaria officinalis and V. locusta significantly deterred A. lusitanicus from feeding. The small effects of some extracts may be due to a poor extraction efficiency or an insufficient feeding inhibition capacity of these extracts.     

SEM studies on vessels in ferns. 11. Ophioglossum

With scanning electron microscopy (SEM), the nature of metaxylem vessel elements and tracheids was examined in Ophioglossum crotalophomides, 0. pendulum subsp. falcatum , and 0. vulgatum roots and rhizomes. Vessels were identified in all species. End walls of vessel elements, which bear perforations, are like lateral wall pitting of those elements in the secondary wall framework and differ only in absence of pit membranes or presence of pit membrane remnants. Some of the perforations contain pit membrane remnants that have large pores, small porosities, or are threadlike or weblike in structure. Dimorphic perforations were found in some vessel elements of rhizomes of 0. pendulum subsp. falcatum. Tracheids are very likely present in addition to vessels in all three species. The secondary wall framework of both tracheids and vessels is basically scalariform, although deviations in pattern are present. Vessel elements of Ophiglossum are entirely comparable to those of leptosporangiate ferns.     

神经网络在蛋白质二级结构预测中的应用

介绍了蛋白质二级结构预测的研究意义,讨论了用在蛋白质二级结构预测方面的神经网络设计问题,并且较详尽地评述了近些年来用神经网络方法在蛋白质二级结构预测中的主要工作进展情况,展望了蛋白质结构预测的前景。     

Informative characteristics of 12 divergent domains in complete large subunit rDNA sequences from the harmful dinoflagellate genus, Alexandrium (Dinophyceae)

The genus Alexandrium includes organisms of interest, both for the study of dinoflagellate evolution and for their impacts as toxic algae affecting human health and fisheries. Only partial large subunit (LSU) rDNA sequences of Alexandrium and other dinoflagellates are available, although they contain much genetic information. Here, we report complete LSU rDNA sequences from 11 strains of Alexandrium, including Alexandrium affine, Alexandrium catenella, Alexandrium fundyense, Alexandrium minutum, and Alexandrium tamarense, and discuss their segmented domains and structure. Putative LSU rRNA coding regions were recorded to be around 3,400 bp long. Their GC content (about 43.7%) is among the lowest when compared with other organisms. Furthermore, no AT-rich regions were found in Alexandrium LSU rDNA, although a low GC content was recorded within the LSU rDNA. No intron-like sequences were found. The secondary structure of the LSU rDNA and parsimony analyses showed that most variation in LSU rDNA is found in the divergent (D) domains with the D2 region being the most informative. This high D domain variability can allow members of the diverse Alexandrium genus to be categorized at the species level. In addition, phylogenetic analysis of the alveolate group using the complete LSU sequences strongly supported previous findings that the dinoflagellates and apicomplexans form a clade.     

植物毛状根的培养及其化学进展：2.植物毛状根的次生代谢

本文介绍了毛状根的次生代谢调控、次生代谢物质的生产、生物转化、生物合成以及工业化应用。     

东北次生林主要树种比叶面积对光照强度的响应

通过测定不同光照条件下（15％透光、30％透光、60％透光、全光）东北次生林主要树种（红松、红皮云杉、胡桃楸、水曲柳和黄波罗）的比叶面积,探讨了不同树种对光照变化的响应与适应。结果表明:不同树种比叶面积存在明显的差异,尤其是常绿针叶树种与落叶树种之间差异显著（P<0.001）,指示不同功能型树种存在不同的生存策略;随着光照强度降低,所有树种比叶面积呈现增加的趋势,尤其是弱光照（15％）和低光照（30％）相对于全光和中光照（60％）差异显著（P<0.05）;不同树种比叶面积随光照强度的变化幅度明显不同,且变化最显著的光照区域也有所不同;不同年龄红松比叶面积的变化趋势一致,但变幅不同,4年生幼苗对光照响应则更为明显。本研究结果表明,所有树种均能通过改变叶形态来适应光照条件的变化,在低光条件下通过增加单位质量叶面积,提高叶片光捕获能力;但各树种对光照强度变化的不同响应则表明树种之间不同的光适应机制,这对森林生态系统内部树种的共生具有重要意义;年龄较小的幼苗对光照的强响应指示其在植物更新过程中叶片水平上生理生态学机理研究中的重要性。     

Resilience of tropical rain forests: tree community reassembly in secondary forests

Understanding the recovery dynamics of ecosystems presents a major challenge in the human-impacted tropics. We tested whether secondary forests follow equilibrium or non-equilibrium dynamics by evaluating community reassembly over time, across different successional stages, and among multiple life stages. Based on long-term and static data from six 1-ha plots in NE Costa Rica, we show that secondary forests are undergoing reassembly of canopy tree and palm species composition through the successful recruitment of seedlings, saplings, and young trees of mature forest species. Such patterns were observed over time within sites and across successional stages. Floristic reassembly in secondary forests showed a clear convergence with mature forest community composition, supporting an equilibrium model. This resilience stems from three key factors co-occurring locally: high abundance of generalist species in the regional flora, high levels of seed dispersal, and local presence of old-growth forest remnants.