Role of the central cations in the mechanical unfolding of DNA and RNA G-quadruplexes.

Cations are known to mediate diverse interactions in nucleic acids duplexes but they are critical in the arrangement of four-stranded structures. Here, we use all-atom molecular dynamics simulations with explicit solvent to analyse the mechanical unfolding of representative intramolecular G-quadruplex structures: a parallel, a hybrid and an antiparallel DNA and a parallel RNA, in the presence of stabilising cations. We confirm the stability of these conformations in the presence of [Formula: see text] central ions and observe distortions from the tetrad topology in their absence. Force-induced unfolding dynamics is then investigated. We show that the unfolding events in the force-extension curves are concomitant to the loss of coordination between the central ions and the guanines of the G-quadruplex. We found lower ruptures forces for the parallel configuration with respect to the antiparallel one, while the behaviour of the force pattern of the parallel RNA appears similar to the parallel DNA. We anticipate that our results will be essential to interpret the fine structure rupture profiles in stretching assays at high resolution and will shed light on the mechanochemical activity of G-quadruplex-binding machinery

Unfolding mechanism and free energy landscape of single, stable, alpha helices at low pull speeds

Single alpha helices (SAHs) stable in isolated form are often found in motor proteins where they bridge functional domains. Understanding the mechanical response of SAHs is thus critical to understand their function. The quasi-static force-extension relation of a small number of SAHs is known from single-molecule experiments. Unknown, or still controversial, are the molecular scale details behind those observations. We show that the deformation mechanism of SAHs pulled from the termini at pull speeds approaching the quasi-static limit differs from that of typical helices found in proteins, which are stable only when interacting with other protein domains. Using molecular dynamics simulations with atomistic resolution at low pull speeds previously inaccessible to simulation, we show that SAHs start unfolding from the termini at all pull speeds we investigated. Unfolding proceeds residue-by-residue and hydrogen bond breaking is not the main event determining the barrier to unfolding. We use the molecular simulation data to test the cooperative Sticky Chain model. This model yields excellent fits of the force-extension curves and quantifies the distance, xE = 0.13 nm, to the transition state, the natural frequency of bond vibration, ν0 = 0.82 ns−1, and the height, V0=2.9 kcal/mol, of the free energy barrier associated with the deformation of single residues. Our results demonstrate that the Sticky Chain model could advantageously be used to analyze experimental force-extension curves of SAHs and other biopolymers

Extracellular cysteine in connexins: Role as redox sensors

Indexación: Scopus.Connexin-based channels comprise hemichannels and gap junction channels. The opening of hemichannels allow for the flux of ions and molecules from the extracellular space into the cell and vice versa. Similarly, the opening of gap junction channels permits the diffusional exchange of ions and molecules between the cytoplasm and contacting cells. The controlled opening of hemichannels has been associated with several physiological cellular processes; thereby unregulated hemichannel activity may induce loss of cellular homeostasis and cell death. Hemichannel activity can be regulated through several mechanisms, such as phosphorylation, divalent cations and changes in membrane potential. Additionally, it was recently postulated that redox molecules could modify hemichannels properties in vitro. However, the molecular mechanism by which redox molecules interact with hemichannels is poorly understood. In this work, we discuss the current knowledge on connexin redox regulation and we propose the hypothesis that extracellular cysteines could be important for sensing changes in redox potential. Future studies on this topic will offer new insight into hemichannel function, thereby expanding the understanding of the contribution of hemichannels to disease progression.http://journal.frontiersin.org/article/10.3389/fphys.2016.00001/ful

Obtaining and Structural Characterization of M-type Hexaferrites Doped with Two Cations in the Fe3+ Sites

A study of the microstructural and structural properties of M-type barium hexaferrites (BaM) samples doped with two dopants in the Fe3+ sites: (Co3+, Al3+), (Co2+, Ti4+) and (Co2+, Sn4+) is reported. The samples were obtained using the conventional ceramic method. The structure was investigated by using of X-ray diffraction (XRD) to determine the dopant distribution in the Fe3+ sites

Optimization of Chaetoceros gracilis microalgae production for fish feeding using an airlift photobioreactor

An experimental procedure was carried out to maximize Chaetoceros gracilis growth. Chaetoceros gracilis, marine microalgae, is considered for feeding fisheries with no GMO (Genetically Modified Organisms) to avoid human health hazards. Furthermore, following United Nations Resolution on water, the microalgae is grown in photobioreactors due to its low water usage. To maximize the microalgae growth, an experimental design was carried out to analyze the effects of Light Intensity, CO2 supply per day, Sparger type, Photoperiod and Inlet airflow, pH and water temperature were monitored but not controlled. It was found that Light intensity and CO2 supply per day have statistical significance. Out of three possible scenarios, 1700 lux and 80 gr/day of CO2, leads to a cell density at day three of 310×104 cel/mL which represents 20% more of the density attained in day two under bag (standard) growing conditions. It was also found that water Ph has also a strong effect over cell density

Résultats électroencéphalographiques dans 33 cas de tumeurs intracraniennes chirurgicalement vérififes

Escola Paulista de MedicinaUniv. de São Paulo Fac. Med.Instituto de Electrencefalografia (São Paulo)Escola Paulista de Medicina Serviço de NeurologiaUNIFESP, EPM, Serviço de NeurologiaSciEL

Videofonograma

Pensar a imagem em movimento como artifício disparador de significações que cingem o tema da dissertação, que dê e que abra visibilidade ao acervo que reuni do mundo camponês aquilo que me irrompe e aquilo que penso ser suas erupções - estas pautadas pelo nucleação política que a movimentação social organizada no campo gera e coaduna. Neste universo, que semânticas (visuais) são translúcidas, ou pretende-se que sejam, e quais não se fixam, não são dadas nem estabelecem referência na gramática do real? O vídeo é eleito como linguagem que manifesta a instabilidade fronteiriça entre reminiscência e imaginação; educação, arte e divulgação; estética e política

Head movement and its relation to hearing

Head position at any point in time plays a fundamental role in shaping the auditory information that reaches a listener, information that continuously changes as the head moves and reorients to different listening situations. The connection between hearing science and the kinesthetics of head movement has gained interest due to technological advances that have increased the feasibility of providing behavioral and biological feedback to assistive listening devices that can interpret movement patterns that reflect listening intent. Increasing evidence also shows that the negative impact of hearing deficits on mobility, gait, and balance may be mitigated by prosthetic hearing device intervention. Better understanding of the relationships between head movement, full body kinetics, and hearing health, should lead to improved signal processing strategies across a range of assistive and augmented hearing devices. The purpose of this review is to introduce the wider hearing community to the kinesiology of head movement and to place it in the context of hearing and communication with the goal of expanding the field of ecologically-specific listener behavior