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‣ The Saccharomyces cerevisiae aquaporin Aqy1 is involved in sporulation

Sidoux-Walter, Frédéric; Pettersson, Nina; Hohmann, Stefan
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Aquaporins mediate rapid selective water transport across biological membranes. Elucidation of their precise physiological roles promises important insight into cellular and organismal osmoregulation. The genome of the yeast Saccharomyces cerevisiae encodes two similar but differentially regulated aquaporins. Here, we show that expression of AQY1 is stimulated during sporulation and that the Aqy1 protein is detectable exclusively in spore membranes. When spores are rapidly frozen, those that lack Aqy1 survive better, providing for a functional test of active spore water channels. Under ambient conditions, lack of Aqy1 reduces spore fitness. Because this reduction is independent from germination conditions, Aqy1 may be important during spore formation rather than subsequent maintenance or germination. Indeed, it seems that Aqy1 is degraded after spores have been formed and during germination. Taken together, Aqy1 is developmentally controlled and may play a role in spore maturation, probably by allowing water outflow. Taken together, we demonstrate a functional role of an aquaporin in gametogenesis, as well as in the formation of durable structures such as spores, a role that may have wider biological and medical implications.

‣ Experimental evolution of conflict mediation between genomes

Sachs, Joel L.; Bull, James J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Transitions to new levels of biological complexity often require cooperation among component individuals, but individual selection among those components may favor a selfishness that thwarts the evolution of cooperation. Biological systems with elements of cooperation and conflict are especially challenging to understand because the very direction of evolution is indeterminate and cannot be predicted without knowing which types of selfish mutations and interactions can arise. Here, we investigated the evolution of two bacteriophages (f1 and IKe) experimentally forced to obey a life cycle with elements of cooperation and conflict, whose outcome could have ranged from extinction of the population (due to selection of selfish elements) to extreme cooperation. Our results show the de novo evolution of a conflict mediation system that facilitates cooperation. Specifically, the two phages evolved to copackage their genomes into one protein coat, ensuring cotransmission with each other and virtually eliminating conflict. Thereafter, IKe evolved such extreme genome reduction that it lost the ability to make its own virions independent of f1. Our results parallel a variety of conflict mediation mechanisms existing in nature: evolution of reduced genomes in symbionts...

‣ Surviving heat shock: Control strategies for robustness and performance

El-Samad, H.; Kurata, H.; Doyle, J. C.; Gross, C. A.; Khammash, M.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Molecular biology studies the cause-and-effect relationships among microscopic processes initiated by individual molecules within a cell and observes their macroscopic phenotypic effects on cells and organisms. These studies provide a wealth of information about the underlying networks and pathways responsible for the basic functionality and robustness of biological systems. At the same time, these studies create exciting opportunities for the development of quantitative and predictive models that connect the mechanism to its phenotype then examine various modular structures and the range of their dynamical behavior. The use of such models enables a deeper understanding of the design principles underlying biological organization and makes their reverse engineering and manipulation both possible and tractable The heat shock response presents an interesting mechanism where such an endeavor is possible. Using a model of heat shock, we extract the design motifs in the system and justify their existence in terms of various performance objectives. We also offer a modular decomposition that parallels that of traditional engineering control architectures.

‣ Sterol structure determines the separation of phases and the curvature of the liquid-ordered phase in model membranes

Bacia, Kirsten; Schwille, Petra; Kurzchalia, Teymuras
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The existence of lipid rafts in biological membranes in vivo is still debated. In contrast, the formation of domains in model systems has been well documented. In giant unilamellar vesicles (GUVs) prepared from ternary mixtures of dioleoyl-phosphatidylcholine/sphingomyelin/cholesterol, a clear separation of liquid-disordered and sphingomyelin-enriched, liquid-ordered phases could be observed. This phase separation can lead to the fission of the liquid-ordered phase from the vesicle. Here we show that in cholesterol-containing GUVs, the phase separation can involve dynamic redistribution of lipids from one phase into another as a result of a cross-linking perturbation. We found that the molecular structure of a sterol used for the preparation of GUVs determines (i) its ability to induce phase separation and (ii) the curvature (positive or negative) of the formed liquid-ordered phase. As a consequence, the latter can pinch off to the outside or inside of the vesicle. Remarkably, some mixtures of sterols induce liquid-ordered domains exhibiting both positive and negative curvature, which can lead to a new type of budding behavior in GUVs. Our findings could have implications for the role of sterols in various cell-biological processes such as budding of secretory vesicles...

‣ Automated microscope system for determining factors that predict neuronal fate

Arrasate, Montserrat; Finkbeiner, Steven
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Unraveling cause-and-effect relationships in the nervous system is challenging because some biological processes begin stochastically, take a significant amount of time to unfold, and affect small neuronal subpopulations that can be difficult to isolate and measure. Single-cell approaches are slow, subject to user bias, and sometimes too laborious to achieve sample sizes large enough to detect important effects. Here, we describe an automated imaging and analysis system that enables us to follow the fates of individual cells and intracellular proteins over time. Observations can be quantified in a high-throughput manner with minimal user bias. We have adapted survival analysis methods to determine whether and how factors measured during longitudinal analysis predict a particular biological outcome. The ability to monitor complex processes at single-cell resolution quickly, quantitatively, and over long intervals should have wide applications for biology.

‣ Characterization of Dicer-deficient murine embryonic stem cells

Murchison, Elizabeth P.; Partridge, Janet F.; Tam, Oliver H.; Cheloufi, Sihem; Hannon, Gregory J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Dicer is an RNase III-family nuclease that initiates RNA interference (RNAi) and related phenomena by generation of the small RNAs that determine the specificity of these gene silencing pathways. We have previously shown that Dicer is essential for mammalian development, with Dicer-deficient mice dying at embryonic day 7.5 with a lack of detectable multipotent stem cells. To permit a more detailed investigation of the biological roles of Dicer, we have generated embryonic stem cell lines in which their single Dicer gene can be conditionally inactivated. As expected, Dicer loss compromises maturation of microRNAs and leads to a defect in gene silencing triggered by long dsRNAs. However, the absence of Dicer does not affect the ability of small interfering RNAs to repress gene expression. Of interest, Dicer loss does compromise the proliferation of ES cells, possibly rationalizing the phenotype previously observed in Dicer-null animals. Dicer loss also affects the abundance of transcripts from mammalian centromeres but does so without a pronounced affect on histone modification status at pericentric repeats or methylation of centromeric DNA. These studies provide a conditional model of RNAi deficiency in mammals that will permit the dissection of the biological roles of the RNAi machinery in cultured mammalian cells.

‣ Genetically attenuated, P36p-deficient malarial sporozoites induce protective immunity and apoptosis of infected liver cells

van Dijk, Melissa R.; Douradinha, Bruno; Franke-Fayard, Blandine; Heussler, Volker; van Dooren, Maaike W.; van Schaijk, Ben; van Gemert, Geert-Jan; Sauerwein, Robert W.; Mota, Maria M.; Waters, Andrew P.; Janse, Chris J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Immunization with Plasmodium sporozoites that have been attenuated by γ-irradiation or specific genetic modification can induce protective immunity against subsequent malaria infection. The mechanism of protection is only known for radiation-attenuated sporozoites, involving cell-mediated and humoral immune responses invoked by infected hepatocytes cells that contain long-lived, partially developed parasites. Here we analyzed sporozoites of Plasmodium berghei that are deficient in P36p (p36p-), a member of the P48/45 family of surface proteins. P36p plays no role in the ability of sporozoites to infect and traverse hepatocytes, but p36p- sporozoites abort during development within the hepatocyte. Immunization with p36p- sporozoites results in a protective immunity against subsequent challenge with infectious wild-type sporozoites, another example of a specifically genetically attenuated sporozoite (GAS) conferring protective immunity. Comparison of biological characteristics of p36p- sporozoites with radiation-attenuated sporozoites demonstrates that liver cells infected with p36p- sporozoites disappear rapidly as a result of apoptosis of host cells that may potentiate the immune response. Such knowledge of the biological characteristics of GAS and their evoked immune responses are essential for further investigation of the utility of an optimized GAS-based malaria vaccine.

‣ Mechanism of radiation-induced bystander effect: Role of the cyclooxygenase-2 signaling pathway

Zhou, Hongning; Ivanov, Vladimir N.; Gillespie, Joseph; Geard, Charles R.; Amundson, Sally A.; Brenner, David J.; Yu, Zengliang; Lieberman, Howard B.; Hei, Tom K.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The radiation-induced bystander effect is defined as “the induction of biological effects in cells that are not directly traversed by a charged particle but are in close proximity to cells that are.” Although these bystander effects have been demonstrated with a variety of biological endpoints in both human and rodent cell lines (as well as in 3D tissue samples), the mechanism of the phenomenon is not known. Although gap junction communication and the presence of soluble mediator(s) are both known to play important roles in the bystander response, the precise signaling molecules have yet to be identified. By using the Columbia University charged particle beam in conjunction with a strip dish design, we show here that the cyclooxygenase-2 (COX-2, also known as prostaglandin endoperoxide synthase-2) signaling cascade plays an essential role in the bystander process. Treatment of bystander cells with NS-398, which suppresses COX-2 activity, significantly reduced the bystander effect. Because the critical event of the COX-2 signaling is the activation of the mitogen-activated protein kinase pathways, our finding that inhibition of the extracellular signal-related kinase phosphorylation suppressed bystander response further confirmed the important role of mitogen-activated protein kinase signaling cascade in the bystander process. These results provide evidence that the COX-2-related pathway...

‣ Generation of tissue-specific transgenic birds with lentiviral vectors

Scott, Benjamin B.; Lois, Carlos
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Birds are of great interest for a variety of research purposes, and effective methods for manipulating the avian genome would greatly accelerate progress in fields that rely on birds as model systems for biological research, such as developmental biology and behavioral neurobiology. Here, we describe a simple and effective method for producing transgenic birds. We used lentiviral vectors to produce transgenic quails that express GFP driven by the human synapsin gene I promoter. Expression of GFP was specific to neurons and consistent across multiple generations. Expression was sufficient to allow visualization of individual axons and dendrites of neurons in vivo by intrinsic GFP fluorescence. Tissue-specific transgene expression at high levels provides a powerful tool for biological research and opens new avenues for genetic manipulation in birds.

‣ The stress-regulated protein M6a is a key modulator for neurite outgrowth and filopodium/spine formation

Alfonso, Julieta; Fernández, María E.; Cooper, Benjamin; Flugge, Gabriele; Frasch, Alberto C.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Neuronal remodeling is a fundamental process by which the brain responds to environmental influences, e.g., during stress. In the hippocampus, chronic stress causes retraction of dendrites in CA3 pyramidal neurons. We have recently identified the glycoprotein M6a as a stress-responsive gene in the hippocampal formation. This gene is down-regulated in the hippocampus of both socially and physically stressed animals, and this effect can be reversed by antidepressant treatment. In the present work, we analyzed the biological function of the M6a protein. Immunohistochemistry showed that the M6a protein is abundant in all hippocampal subregions, and subcellular analysis in primary hippocampal neurons revealed its presence in membrane protrusions (filopodia/spines). Transfection experiments revealed that M6a overexpression induces neurite formation and increases filopodia density in hippocampal neurons. M6a knockdown with small interference RNA methodology showed that M6a low-expressing neurons display decreased filopodia number and a lower density of synaptophysin clusters. Taken together, our findings indicate that M6a plays an important role in neurite/filopodium outgrowth and synapse formation. Therefore, reduced M6a expression might be responsible for the morphological alterations found in the hippocampus of chronically stressed animals. Potential mechanisms that might explain the biological effects of M6a are discussed.

‣ Mapping of orthologous genes in the context of biological pathways: An application of integer programming

Mao, Fenglou; Su, Zhengchang; Olman, Victor; Dam, Phuongan; Liu, Zhijie; Xu, Ying
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Mapping biological pathways across microbial genomes is a highly important technique in functional studies of biological systems. Existing methods mainly rely on sequence-based orthologous gene mapping, which often leads to suboptimal mapping results because sequence-similarity information alone does not contain sufficient information for accurate identification of orthology relationship. Here we present an algorithm for pathway mapping across microbial genomes. The algorithm takes into account both sequence similarity and genomic structure information such as operons and regulons. One basic premise of our approach is that a microbial pathway could generally be decomposed into a few operons or regulons. We formulated the pathway-mapping problem to map genes across genomes to maximize their sequence similarity under the constraint that the mapped genes be grouped into a few operons, preferably coregulated in the target genome. We have developed an integer-programming algorithm for solving this constrained optimization problem and implemented the algorithm as a computer software program, p-map. We have tested p-map on a number of known homologous pathways. We conclude that using genomic structure information as constraints could greatly improve the pathway-mapping accuracy over methods that use sequence-similarity information alone.

‣ Networks of gold nanoparticles and bacteriophage as biological sensors and cell-targeting agents

Souza, Glauco R.; Christianson, Dawn R.; Staquicini, Fernanda I.; Ozawa, Michael G.; Snyder, Evan Y.; Sidman, Richard L.; Miller, J. Houston; Arap, Wadih; Pasqualini, Renata
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Biological molecular assemblies are excellent models for the development of nanoengineered systems with desirable biomedical properties. Here we report an approach for fabrication of spontaneous, biologically active molecular networks consisting of bacteriophage (phage) directly assembled with gold (Au) nanoparticles (termed Au–phage). We show that when the phage are engineered so that each phage particle displays a peptide, such networks preserve the cell surface receptor binding and internalization attributes of the displayed peptide. The spontaneous organization of these targeted networks can be manipulated further by incorporation of imidazole (Au–phage–imid), which induces changes in fractal structure and near-infrared optical properties. The networks can be used as labels for enhanced fluorescence and dark-field microscopy, surface-enhanced Raman scattering detection, and near-infrared photon-to-heat conversion. Together, the physical and biological features within these targeted networks offer convenient multifunctional integration within a single entity with potential for nanotechnology-based biomedical applications.

‣ Microparadigms: Chains of collective reasoning in publications about molecular interactions

Rzhetsky, Andrey; Iossifov, Ivan; Loh, Ji Meng; White, Kevin P.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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We analyzed a very large set of molecular interactions that had been derived automatically from biological texts. We found that published statements, regardless of their verity, tend to interfere with interpretation of the subsequent experiments and, therefore, can act as scientific “microparadigms,” similar to dominant scientific theories [Kuhn, T. S. (1996) The Structure of Scientific Revolutions (Univ. Chicago Press, Chicago)]. Using statistical tools, we measured the strength of the influence of a single published statement on subsequent interpretations. We call these measured values the momentums of the published statements and treat separately the majority and minority of conflicting statements about the same molecular event. Our results indicate that, when building biological models based on published experimental data, we may have to treat the data as highly dependent-ordered sequences of statements (i.e., chains of collective reasoning) rather than unordered and independent experimental observations. Furthermore, our computations indicate that our data set can be interpreted in two very different ways (two “alternative universes”): one is an “optimists’ universe” with a very low incidence of false results (<5%)...

‣ Neutral and adaptive variation in gene expression

Whitehead, Andrew; Crawford, Douglas L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Variation among populations in gene expression should be related to the accumulation of random-neutral changes and evolution by natural selection. The following evolutionary analysis has general applicability to biological and medical science because it accounts for genetic relatedness and identifies patterns of expression variation that are affected by natural selection. To identify genes evolving by natural selection, we allocate the maximum among-population variation to genetic distance and then examine the remaining variation relative to a hypothesized important ecological parameter (temperature). These analyses measure the expression of metabolic genes in common-gardened populations of the fish Fundulus heteroclitus whose habitat is distributed along a steep thermal gradient. Although much of the variation in gene expression fits a null model of neutral drift, the variation in expression for 22% of the genes that regress with habitat temperature was far greater than could be accounted for by genetic distance alone. The most parsimonious explanation for among-population variation for these genes is evolution by natural selection. In addition, many metabolic genes have patterns of variation incongruent with neutral evolution: They have too much or too little variation. These patterns of biological variation in expression may reflect important physiological or ecological functions.

‣ The intricate side of systems biology

Voit, Eberhard; Neves, Ana Rute; Santos, Helena
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The combination of high-throughput methods of molecular biology with advanced mathematical and computational techniques has propelled the emergent field of systems biology into a position of prominence. Unthinkable a decade ago, it has become possible to screen and analyze the expression of entire genomes, simultaneously assess large numbers of proteins and their prevalence, and characterize in detail the metabolic state of a cell population. Although very important, the focus on comprehensive networks of biological components is only one side of systems biology. Complementing large-scale assessments, and sometimes at the risk of being forgotten, are more subtle analyses that rationalize the design and functioning of biological modules in exquisite detail. This intricate side of systems biology aims at identifying the specific roles of processes and signals in smaller, fully regulated systems by computing what would happen if these signals were lacking or organized in a different fashion. We exemplify this type of approach with a detailed analysis of the regulation of glucose utilization in Lactococcus lactis. This organism is exposed to alternating periods of glucose availability and starvation. During starvation, it accumulates an intermediate of glycolysis...

‣ Identifying genes important for spermatogonial stem cell self-renewal and survival

Oatley, Jon M.; Avarbock, Mary R.; Telaranta, Aino I.; Fearon, Douglas T.; Brinster, Ralph L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Spermatogonial stem cells (SSCs) are the foundation for spermatogenesis and, thus, preservation of a species. Because of stem cell rarity, studying their self-renewal is greatly facilitated by in vitro culture of enriched biologically active cell populations. A recently developed culture method identified glial cell line-derived neurotrophic factor (GDNF) as the essential growth factor that supports in vitro self-renewal of SSCs and results in an increase in their number. This system is a good model to study mechanisms of stem cell self-renewal because of the well defined culture conditions, enriched cell population, and available transplantation assay. By withdrawing and replacing GDNF in culture medium, we identified regulated expression of many genes by using microarray analysis. The expression levels of six of these genes were dramatically decreased by GDNF withdrawal and increased by GDNF replacement. To demonstrate the biological significance of the identified GDNF-regulated genes, we examined the importance of the most responsive of the six, bcl6b, a transcriptional repressor. By using siRNA to reduce transcript levels, Bcl6b was shown to be crucial for SSC maintenance in vitro. Moreover, evaluation of Bcl6b-null male testes revealed degeneration and/or absence of active spermatogenesis in 24 ± 7% of seminiferous tubules. These data suggest that Bcl6b is an important molecule in SSC self-renewal and validate the biological relevance of the GDNF-regulated genes identified through microarray analysis. In addition...

‣ Aspm specifically maintains symmetric proliferative divisions of neuroepithelial cells

Fish, Jennifer L.; Kosodo, Yoichi; Enard, Wolfgang; Pääbo, Svante; Huttner, Wieland B.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The ASPM (abnormal spindle-like microcephaly-associated) protein has previously been implicated in the determination of human cerebral cortical size, but the cell biological basis of this regulation has not been studied. Here we investigate the role of Aspm in mouse embryonic neuroepithelial (NE) cells, the primary stem and progenitor cells of the mammalian brain. Aspm was found to be concentrated at mitotic spindle poles of NE cells and to be down-regulated with their switch from proliferative to neurogenic divisions. Upon RNA interference in telencephalic NE cells, Aspm mRNA is reduced, mitotic spindle poles lack Aspm protein, and the cleavage plane of NE cells is less frequently oriented perpendicular to the ventricular surface of the neuroepithelium. The alteration in the cleavage plane orientation of NE cells increases the probability that these highly polarized cells undergo asymmetric division, i.e., that apical plasma membrane is inherited by only one of the daughter cells. Concomitant with the resulting increase in abventricular cells in the ventricular zone, a larger proportion of NE cell progeny is found in the neuronal layer, implying a reduction in the number of NE progenitor cells upon Aspm knock-down relative to control. Our results demonstrate that Aspm is crucial for maintaining a cleavage plane orientation that allows symmetric...

‣ A family of conserved noncoding elements derived from an ancient transposable element

Xie, Xiaohui; Kamal, Michael; Lander, Eric S.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The evolutionary origin of the conserved noncoding elements (CNEs) in the human genome remains poorly understood but may hold important clues to their biological functions. Here, we report the discovery of a CNE family with ≈124 instances in the human genome that demonstrates a clear signature of having been derived from an ancient transposon. The CNE family is also present in the chicken genome, although typically not at orthologous locations. The CNE family is closely related to the active transposon SINE3 in zebrafish and also to a previously uncharacterized transposon in the coelacanth, the so-called “living fossil” belonging to the lobe-finned fish lineage. The mammal, bird, zebrafish, and coelacanth families all share a highly similar core element of ≈180 bp but have important differences in their 5′ and 3′ ends. The core element has thus been preserved over 450 million years of evolution, implying an important biological function. In addition, we identify 95 additional CNE families that likely predate the mammalian radiation. The results highlight both the creative role of transposons and the importance of CNE families.

‣ A microrotary motor powered by bacteria

Hiratsuka, Yuichi; Miyata, Makoto; Tada, Tetsuya; Uyeda, Taro Q. P.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Biological molecular motors have a number of unique advantages over artificial motors, including efficient conversion of chemical energy into mechanical work and the potential for self-assembly into larger structures, as is seen in muscle sarcomeres and bacterial and eukaryotic flagella. The development of an appropriate interface between such biological materials and synthetic devices should enable us to realize useful hybrid micromachines. Here we describe a microrotary motor composed of a 20-μm-diameter silicon dioxide rotor driven on a silicon track by the gliding bacterium Mycoplasma mobile. This motor is fueled by glucose and inherits some of the properties normally attributed to living systems.

‣ Anomalous resonance in a nanomechanical biosensor

Gupta, Amit K.; Nair, Pradeep R.; Akin, Demir; Ladisch, Michael R.; Broyles, Steve; Alam, Muhammad A.; Bashir, Rashid
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The decrease in resonant frequency (−Δωr) of a classical cantilever provides a sensitive measure of the mass of entities attached on its surface. This elementary phenomenon has been the basis of a new class of bio-nanomechanical devices as sensing components of integrated microsystems that can perform rapid, sensitive, and selective detection of biological and biochemical entities. Based on classical analysis, there is a widespread perception that smaller sensors are more sensitive (sensitivity ≈ −0.5ωr/mC, where mC is the mass of the cantilever), and this notion has motivated scaling of biosensors to nanoscale dimensions. In this work, we show that the response of a nanomechanical biosensor is far more complex than previously anticipated. Indeed, in contrast to classical microscale sensors, the resonant frequencies of the nanosensor may actually decrease or increase after attachment of protein molecules. We demonstrate theoretically and experimentally that the direction of the frequency change arises from a size-specific modification of diffusion and attachment kinetics of biomolecules on the cantilevers. This work may have broad impact on microscale and nanoscale biosensor design, especially when predicting the characteristics of bio-nanoelectromechanical sensors functionalized with biological capture molecules.