Gating and inward rectifying properties of the MthK K+ channel with and without the gating ring

In MthK, a Ca2+-gated K+ channel from Methanobacterium thermoautotrophicum, eight cytoplasmic RCK domains form an octameric gating ring that controls the intracellular gate of the ion conduction pore. The binding of Ca2+ ions to the RCK domains alters the conformation of the gating ring, thereby opening the gate. In the present study, we examined the Ca2+- and pH-regulated gating and the rectifying conduction properties of MthK at the single-channel level. The open probability (Po) of MthK exhibits a sigmoidal relationship with intracellular [Ca2+], and a Hill coefficient >1 is required to describe the dependence of Po on [Ca2+], suggesting cooperative Ca2+ activation of the channel. Additionally, intracellular Ca2+ also blocks the MthK pore in a voltage-dependent manner, rendering an apparently inwardly rectifying I-V relation. Intracellular pH has a dual effect on MthK gating. Below pH 7.5, the channel becomes insensitive to Ca2+. This occurs because the gating ring is structurally unstable at this pH and tends to disassemble (Ye, S., Y. Li, L. Chen, and Y. Jiang. 2006. Cell. 126:1161-1173). In contrast, above pH 7.5, a further increase in pH shifts the Po-[Ca2+] relation towards a lower Ca2+ concentration, augments Po at saturating [Ca2+], and activates the channel even in the absence of Ca2+. Channel activity is marked by bursts of rapid openings and closings separated by relatively longer interburst closings. The duration of interburst closing and the burst length are highly Ca2+ and pH dependent, whereas the kinetics of intraburst events is Ca2+ and pH independent. The rapid intraburst openings and closings are also observed with the isolated MthK pore lacking the attached intracellular gating ring. The fast kinetic events, independent of both Ca2+ and pH, therefore appear to be determined by processes occurring within the ion conduction pore, whereas the slow events reflect the gating process controlled by Ca2+ and pH through the gating ring.     

Evaluation of antimicrobial activity of certain Chinese plants used in folkloric medicine

Six selected plants, belonging to 3 families from Nanjing of China, were extracted with the solvent 95% (v/v) ethanol to yield 11 extracts. The extracts were evaluated for their effects on the growth of eight clinical bacteria, two fungi and one yeast using a modified agar diffusion method. The results showed that the majority of the extracts investigated showed greater activities against the Gram-positive bacteria than against the Gram-negative bacteria, the fungi and the yeast. The strongest antimicrobial activity was exhibited by the stem extracts of Mahonia fortunei against multiresistant Staphylococcus aureus strains, followed by the stem extracts of Mahonia bealei, while Bacillus thuringiensis was the most sensitive to all extracts.     

Self-organizing circuit assembly through spatiotemporally coordinated neuronal migration within geometric constraints

Background

Neurons are dynamically coupled with each other through neurite-mediated adhesion during development. Understanding the collective behavior of neurons in circuits is important for understanding neural development. While a number of genetic and activity-dependent factors regulating neuronal migration have been discovered on single cell level, systematic study of collective neuronal migration has been lacking. Various biological systems are shown to be self-organized, and it is not known if neural circuit assembly is self-organized. Besides, many of the molecular factors take effect through spatial patterns, and coupled biological systems exhibit emergent property in response to geometric constraints. How geometric constraints of the patterns regulate neuronal migration and circuit assembly of neurons within the patterns remains unexplored.

Methodology/Principal Findings

We established a two-dimensional model for studying collective neuronal migration of a circuit, with hippocampal neurons from embryonic rats on Matrigel-coated self-assembled monolayers (SAMs). When the neural circuit is subject to geometric constraints of a critical scale, we found that the collective behavior of neuronal migration is spatiotemporally coordinated. Neuronal somata that are evenly distributed upon adhesion tend to aggregate at the geometric center of the circuit, forming mono-clusters. Clustering formation is geometry-dependent, within a critical scale from 200 µm to approximately 500 µm. Finally, somata clustering is neuron-type specific, and glutamatergic and GABAergic neurons tend to aggregate homo-philically.

Conclusions/Significance

We demonstrate self-organization of neural circuits in response to geometric constraints through spatiotemporally coordinated neuronal migration, possibly via mechanical coupling. We found that such collective neuronal migration leads to somata clustering, and mono-cluster appears when the geometric constraints fall within a critical scale. The discovery of geometry-dependent collective neuronal migration and the formation of somata clustering in vitro shed light on neural development in vivo.     

PAX6 haplotypes are associated with high myopia in Han chinese

Background

The paired box 6 (PAX6) gene is considered as a master gene for eye development. Linkage of myopia to the PAX6 region on chromosome 11p13 was shown in several studies, but the results for association between myopia and PAX6 were inconsistent so far.

Methodology/Principal Findings

We genotyped 16 single nucleotide polymorphisms (SNPs) in the PAX6 gene and its regulatory regions in an initial study for 300 high myopia cases and 300 controls (Group 1), and successfully replicated the positive results with another independent group of 299 high myopia cases and 299 controls (Group 2). Five SNPs were genotyped in the replication study. The spherical equivalent of subjects with high myopia was ≤−8.0 dioptres. The PLINK package was used for genetic data analysis. No association was found between each of the SNPs and high myopia. However, exhaustive sliding-window haplotype analysis highlighted an important role for rs12421026 because haplotypes containing this SNP were found to be associated with high myopia. The most significant results were given by the 4-SNP haplotype window consisting of rs2071754, rs3026393, rs1506 and rs12421026 (P = 3.54×10⁻¹⁰, 4.06×10⁻¹¹ and 1.56×10⁻¹⁸ for Group 1, Group 2 and Combined Group, respectively) and the 3-SNP haplotype window composed of rs3026393, rs1506 and rs12421026 (P = 5.48×10⁻¹⁰, 7.93×10⁻¹² and 6.28×10⁻²³ for the three respective groups). The results remained significant after correction for multiple comparisons by permutations. The associated haplotyes found in a previous study were also successfully replicated in this study.

Conclusions/Significance

PAX6 haplotypes are associated with susceptibility to the development of high myopia in Chinese. The PAX6 locus plays a role in high myopia.     

Acyl-CoA oxidase from Candida tropicalis

Acyl coenzyme A oxidase (acyl-CoA oxidase) has been isolated in good yield from Candida tropicalis pK 233 grown on n-alkanes. Gel filtration, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and measurement of flavin content suggest that the oxidase is an octamer of Mr 75 000 subunits each containing one flavin. The oxidase yields the red semiquinone form on dithionite or photochemical reduction, slowly forms an N-5 adduct with 0.16 M sulfite at pH 7.4, and is rapidly reduced by borohydride, forming the 3,4-dihydroflavin isomer. The red flavosemiquinone is only kinetically stabilized with respect to disproportionation in the free enzyme but is thermodynamically stabilized on binding enoyl-CoA derivatives. The enzyme is reduced by butyryl-, octanoyl-, and palmitoyl-CoA without formation of prominent long-wavelength bands. Acyl-CoA oxidase and the acyl-CoA dehydrogenases share many similarities in their interaction with CoA derivatives. For example, both enzymes stabilize the anionic radical on binding enoyl-CoA derivatives, both dehydrogenate 2-oxoheptadecyldethio-CoA but cannot utilize S-heptadecyl-CoA, both form long-wavelength bands with CoA persulfide species, and both enzymes are attacked by the suicide substrates 3,4-pentadienoyl-CoA and (methylene-cyclopropyl)acetyl-CoA at the flavin prosthetic group.     

灌水施肥对羊草(Aneurolepidium chinense)草原群落光合速率的影响

对天然羊草群落进行灌水和施肥后,测定了它们(灌水、灌水加施肥和对照)的群落光合速率。结果如下:1.在灌水、施肥加灌水处理后23天测定,处理群落的叶层高度分别比对照高8%和9%;群落LAI分别比对照高68.97%和99.93%;群落生物量分别比对照高41%和65.69%;群落日净光合量分别是对照的2.48倍和3.76倍;最大光合量分别是对照的2.82倍和3.12倍。2.灌水施肥处理后,羊草群落光合速率日变化的类型与对照基本一致,属于双峰型。唯独灌水加施肥群落(处理后3天)是单峰型,没有中午降低现象。看出较好的水肥条件能改变群落的日变化类型。3.在温湿度条件较差时或随着处理时间的推移,处理的效果越显著。第一阶段测定时,灌水、灌水加施肥处理的群落日净光合量分别是对照的1.26和1.17倍。第二阶段测定时,分别是对照的1.40和1.84倍。第三阶段测定时,分别是对照的2.48和3.76倍。     

Phycobilisome from Anabaena Variabilis Kütz. and its Model Conjugates

The model conjugates phycocyanin-allophycocyanin (C-PC-APC) and phycoerythrocyanin-phycocyanin-allophycocyanin (PEC-C-PC-APC) were synthesized by using a heterobifunctional coupling reagent N-succinimidyl-3-(2-pyridyldithio)propionate. The rod-core complex (αβ)₆ ^PCL_RC ²⁷(αβ)₃ ^APCL_C ^8.9 and phycobilisomes were separated from Anabaena variabilis. Energy transfer features for the conjugates and the complexes were compared. The absorption and fluorescence emission spectra indicated that the linker-peptides mediate interaction of phycobiliproteins and prompt energy transfer. The energy transfer in the conjugates was detected by fluorescence emission spectra and confirmed by the addition of dithiothreitol. The conjugates may be used as models for studying the energy transfer mechanism in phycobilisomes. This revised version was published online in September 2006 with corrections to the Cover Date.     

Stomatal conductance is a key parameter to assess limitations to photosynthesis and growth potential in barley genotypes

Fourteen genotypes of barley were compared for response to salinity by monitoring the parameters gas exchange and chlorophyll fluorescence. We present relationships between stomatal conductance (gs) gas exchange chlorophyll fluorescence parameters and aboveground dry matter (AGDM). We found that genetic variability provided a continuum of data for gs across control and saline conditions. We used this continuum of gs values to test the overall relationships between gs and net photosynthesis (A), leaf internal CO2 concentration (Ci), actual quantum yield of PSII electron transport (PhiPSII), relative electron yield over net CO2 assimilation rate (ETR/A), and AGDM. The relationship between gs and A was highly significant (P < 0.0001) for both control and saline treatments, while correlations between gs and Ci, and Ci and A were significant only under control conditions. Unexpectedly, we found positive correlations between gs and PhiPSII (P < 0.0001) for both conditions. A comparison between relationships of gs and A, and gs and PhiPSII seemed to indicate a possible acclimation to salinity at the chloroplastic level. Finally, the relationships between gs and ETR/A were exceptionally strong for both growing conditions (P < 0.0001) indicating that, as gs values were negatively affected in barley by genetics and salinity as main or interactive effects, there was a progressive increase in photorespiration in barley. Overall, we found that stomatal conductance was a key parameter in the study of barley responses to limiting situations for photosynthesis. We also found a strong relationship between AGDM and gs regardless of growing conditions and genotypes. For breeding evaluations to select barley genotypes for salinity tolerance, it may be possible to replace all measurements of gas exchange and chlorophyll fluorescence by the simple use of a porometer.     

Synthesis and in vitro antitumor activity of 4(3H)-quinazolinone derivatives with dithiocarbamate side chains

A series of 4(3H)-quinazolinone derivatives with dithiocarbamate side chains were synthesized and tested for their in vitro antitumor activity against human myelogenous leukemia K562 cells. Among them, (3,4-dihydro-2-methyl-4-oxoquinazolin-6-yl)methyl 4-(4-fluorophenyl)piperazine-1-carbodithioate 8q exhibited significant inhibitory activity against K562 cells with IC(50) value of 0.5 microM.     

Gene Expression of Neuropilin-1 and Its Receptors,VEGF/Semaphorin 3a,in Normal and Cancer Cells

Extracellular domains of the transmembrane glycoprotein, neuropilin-1 (Np1), specifically bind an array of factors and co-receptors including class-3 semaphorins (Sema3a), vascular endothelial growth factor (VEGF), hepatocyte growth factor, platelet-derived growth factor BB, transforming growth factor-β 1 (TGF-β1), and fibroblast growth factor2 (FGF2). Np1 may have a role in immune response, tumor cell growth, and angiogenesis, but its relative expression in comparison to its co-primary receptors, VEGF and Sema3a, is not known. In this study we determined the mRNA expression of Np1 and its co-receptors, VEGF and Sema3a, and the ratio of VEGF/Sema3a in different human and rodent cell lines. Expression of Np1, VEGF and Sema3a is very low in cells derived from normal tissues, but these proteins are highly expressed in tumor-derived cells. Furthermore, the ratio of VEGF/Sema3a is highly variable in different tumor cells. The elevated mRNA expression of Np1 and its putative receptors in tumor cells suggests a role for these proteins in tumor cell migration and angiogenesis. As different tumor cells exhibit varying VEGF/Sema3a ratios, it appears that cancer cells show differential response to angiogenic factors. These results bring to light the individual variation among the cancer-related genes, Np1, VEGF, and Sema3a, and provide an important impetus for the possible personalized therapeutic approaches for cancer patients.