Aggregation and conformational studies on a pentapeptide derivative

Most of the disease causing proteins such as beta amyloid, amylin, and huntingtin protein, which are natively disordered, readily form fibrils consisting of beta-sheet polymers. Though all amyloid fibrils are made up of beta-sheet polymers, not all peptides with predominant beta-sheet content in the native state develop into amyloid fibrils. We hypothesize that stable amyloid like fibril formation may require mixture of different conformational states in the peptide. We have tested this hypothesis on amyloid forming peptide namely HCl(Ile)(5)NH(CH(2)CH(2)O)(3)CH(3) (I). We show peptide I, has propensity to form self-assembled structures of beta-sheets in aqueous solutions. When incubated over a period of time in aqueous buffer, I self assembled into beta sheet like structures with diameters ranging from 30 to 60 A that bind with amyloidophilic dyes like Congo red and Thioflavin T. Interestingly peptide I developed into unstable fibrils after prolonged aging at higher concentration in contrast with the general mature fibril-forming propensity of various amyloid petides known to date.     

Bacterial cell-body rotation driven by a single flagellar motor and by a bundle

Using self-trapped Escherichia coli bacteria that have intact flagellar bundles on glass surfaces, we study statistical fluctuations of cell-body rotation in a steady (unstimulated) state. These fluctuations underline direction randomization of bacterial swimming trajectories and plays a fundamental role in bacterial chemotaxis. A parallel study is also conducted using a classical rotation assay in which cell-body rotation is driven by a single flagellar motor. These investigations allow us to draw the important conclusion that during periods of counterclockwise motor rotation, which contributes to a run, all flagellar motors are strongly correlated, but during the clockwise period, which contributes to a tumble, individual motors are uncorrelated in long times. Our observation is consistent with the physical picture that formation and maintenance of a coherent flagellar bundle is provided by a single dominant flagellum in the bundle.     

Root Exudates Regulate Soil Fungal Community Composition and Diversity

Plants are in constant contact with a community of soil biota that contains fungi ranging from pathogenic to symbiotic. A few studies have demonstrated a critical role of chemical communication in establishing highly specialized relationships, but the general role for root exudates in structuring the soil fungal community is poorly described. This study demonstrates that two model plant species (Arabidopsis thaliana and Medicago truncatula) are able to maintain resident soil fungal populations but unable to maintain nonresident soil fungal populations. This is mediated largely through root exudates: the effects of adding in vitro-generated root exudates to the soil fungal community were qualitatively and quantitatively similar to the results observed for plants grown in those same soils. This effect is observed for total fungal biomass, phylotype diversity, and overall community similarity to the starting community. Nonresident plants and root exudates influenced the fungal community by both positively and negatively impacting the relative abundance of individual phylotypes. A net increase in fungal biomass was observed when nonresident root exudates were added to resident plant treatments, suggesting that increases in specific carbon substrates and/or signaling compounds support an increased soil fungal population load. This study establishes root exudates as a mechanism through which a plant is able to regulate soil fungal community composition.     

Amino-functionalized zirconocene (C5H4CH(Me)NMe2)2ZrCl2, a catalyst for the dehydropolymerization of PhSiH3: Probing of peripheral substituent effects on catalyst dehydropolymerization activity

The amino-functionalized metallocene (C₅H₄CH(Me)NMe₂)₂ZrCl₂, [(Cp^N)₂ZrCl₂] was synthesized by salt metathesis of ZrCl₄ and 2 equiv. of C₅H₄CH(Me)NMe₂Li. The metallocene was obtained in good yield as a mixture of rac and meso diastereomers as established by NMR spectroscopy. The addition of 2 equiv. of n-BuLi to the metallocene (Cp^N)₂ZrCl₂ produced a co-catalyst system which was active, at a 1.0 mol% loading, in the dehydropolymerization of PhSiH₃ to poly(phenylsilane), PPSi. The PPSi was obtained as a 9:1 linear–cyclic mixture (M_w=3850, M_n=2300) as established by GPC analysis; ²⁹Si{¹H} NMR spectroscopy revealed an atactic polymer microstructure.     

The PDZ domain protein PICK1 and the sodium channel BNaC1 interact and localize at mechanosensory terminals of dorsal root ganglion neurons and dendrites of central neurons.

Members of the BNaC/ASIC family of ion channels have been implicated in mechanotransduction and nociception mediated by dorsal root ganglion (DRG) neurons. These ion channels are also expressed in the CNS. We identified the PDZ domain protein PICK1 as an interactor of BNaC1(ASIC2) in a yeast two-hybrid screen. We show by two-hybrid assays, glutathione S-transferase pull-down assays, and coimmunoprecipitations that the BNaC1-PICK1 interaction is specific, and that coexpression of both proteins leads to their clustering in intracellular compartments. The interaction between BNaC1 and PICK1 requires the PDZ domain of PICK1 and the last four amino acids of BNaC1. BNaC1 is similar to two other BNaC/ASIC family members, BNaC2 (ASIC1) and ASIC4, at its extreme C terminus, and we show that PICK1 also interacts with BNaC2. We found that PICK1, like BNaC1 and BNaC2, is expressed by DRG neurons and, like the BNaC1alpha isoform, is present at their peripheral mechanosensory endings. Both PICK1 and BNaC1alpha are also coexpressed by some pyramidal neurons of the cortex, by pyramidal neurons of the CA3 region of hippocampus, and by cerebellar Purkinje neurons, localizing to their dendrites and cell bodies. Therefore, PICK1 interacts with BNaC/ASIC channels and may regulate their subcellular distribution or function in both peripheral and central neurons.     

Evidence for Human Immunodeficiency Virus Type 1 Replication In Vivo in CD14+ Monocytes and Its Potential Role as a Source of Virus in Patients on Highly Active Antiretroviral Therapy

In vitro studies show that human immunodeficiency virus type 1 (HIV-1) does not replicate in freshly isolated monocytes unless monocytes differentiate to monocyte-derived macrophages. Similarly, HIV-1 may replicate in macrophages in vivo, whereas it is unclear whether blood monocytes are permissive to productive infection with HIV-1. We investigated HIV-1 replication in CD14(+) monocytes and resting and activated CD4(+) T cells by measuring the levels of cell-associated viral DNA and mRNA and the genetic evolution of HIV-1 in seven acutely infected patients whose plasma viremia had been <100 copies/ml for 803 to 1,544 days during highly active antiretroviral therapy (HAART). HIV-1 DNA was detected in CD14(+) monocytes as well as in activated and resting CD4(+) T cells throughout the course of study. While significant variation in the decay slopes of HIV-1 DNA was seen among individual patients, viral decay in CD14(+) monocytes was on average slower than that in activated and resting CD4(+) T cells. Measurements of HIV-1 sequence evolution and the concentrations of unspliced and multiply spliced mRNA provided evidence of ongoing HIV-1 replication, more pronounced in CD14(+) monocytes than in resting CD4(+) T cells. Phylogenetic analyses of HIV-1 sequences indicated that after prolonged HAART, viral populations related or identical to those found only in CD14(+) monocytes were seen in plasma from three of the seven patients. In the other four patients, HIV-1 sequences in plasma and the three cell populations were identical. CD14(+) monocytes appear to be one of the potential in vivo sources of HIV-1 in patients receiving HAART.