Página 9 dos resultados de 60878 itens digitais encontrados em 0.037 segundos
Resultados filtrados por Publicador: National Academy of Sciences

‣ De novo design of biomimetic antimicrobial polymers

Tew, Gregory N.; Liu, Dahui; Chen, Bin; Doerksen, Robert J.; Kaplan, Justin; Carroll, Patrick J.; Klein, Michael L.; DeGrado, William F.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em 16/04/2002 Português
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46.675503%
The design of polymers and oligomers that mimic the complex structures and remarkable biological properties of proteins is an important endeavor with both fundamental and practical implications. Recently, a number of nonnatural peptides with designed sequences have been elaborated to provide biologically active structures; in particular, facially amphiphilic peptides built from β-amino acids have been shown to mimic both the structures as well as the biological function of natural antimicrobial peptides such as magainins and cecropins. However, these natural peptides as well as their β-peptide analogues are expensive to prepare and difficult to produce on a large scale, limiting their potential use to certain pharmaceutical applications. We therefore have designed a series of facially amphiphilic arylamide polymers that capture the physical and biological properties of this class of antimicrobial peptides, but are easy to prepare from inexpensive monomers. The design process was aided by molecular calculations with density functional theory-computed torsional potentials. This new class of amphiphilic polymers may be applied in situations where inexpensive antimicrobial agents are required.

‣ Myc and Mad bHLHZ domains possess identical DNA-binding specificities but only partially overlapping functions in vivo

James, Leonard; Eisenman, Robert N.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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46.675503%
The opposing transcriptional activities of the basic-helix–loop–helix-leucine zipper proteins Myc and Mad, taken together with information related to their expression patterns and biological effects, have led to a model of the Myc/Max/Mad network in which Myc and Mad proteins function as antagonists. This antagonism is presumed to operate at the level of genes targeted by these complexes, where Myc:Max activates and Mad:Max represses expression of the same set of genes. However, a detailed analysis of the DNA-binding preferences for Mad proteins has not been performed. Furthermore, the model does not address the findings that Myc:Max indirectly represses transcription of several regulatory genes. To examine these issues relating to DNA-binding specificity and biological responses, we have determined the DNA-binding preferences of Mad1 by using selection and amplification of randomized oligonucleotides and demonstrated that its intrinsic specificity is identical with that of c-Myc. We have also used a chimeric Myc protein, containing a substitution of the entire Mad basic-helix–loop–helix-leucine zipper motif, and shown that it can reproduce the growth-promoting activities of Myc, but not its apoptotic function. Our results suggest that Myc and Mad...

‣ A Bayesian framework for combining heterogeneous data sources for gene function prediction (in Saccharomyces cerevisiae)

Troyanskaya, Olga G.; Dolinski , Kara; Owen, Art B.; Altman, Russ B.; Botstein , David
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
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46.675503%
Genomic sequencing is no longer a novelty, but gene function annotation remains a key challenge in modern biology. A variety of functional genomics experimental techniques are available, from classic methods such as affinity precipitation to advanced high-throughput techniques such as gene expression microarrays. In the future, more disparate methods will be developed, further increasing the need for integrated computational analysis of data generated by these studies. We address this problem with magic (Multisource Association of Genes by Integration of Clusters), a general framework that uses formal Bayesian reasoning to integrate heterogeneous types of high-throughput biological data (such as large-scale two-hybrid screens and multiple microarray analyses) for accurate gene function prediction. The system formally incorporates expert knowledge about relative accuracies of data sources to combine them within a normative framework. magic provides a belief level with its output that allows the user to vary the stringency of predictions. We applied magic to Saccharomyces cerevisiae genetic and physical interactions, microarray, and transcription factor binding sites data and assessed the biological relevance of gene groupings using Gene Ontology annotations produced by the Saccaromyces Genome Database. We found that by creating functional groupings based on heterogeneous data types...

‣ Cu nanocrystal growth on peptide nanotubes by biomineralization: Size control of Cu nanocrystals by tuning peptide conformation

Banerjee, Ipsita A.; Yu, Lingtao; Matsui, Hiroshi
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.675503%
With recent interest in seeking new biologically inspired device-fabrication methods in nanotechnology, a new biological approach was examined to fabricate Cu nanotubes by using sequenced histidine-rich peptide nanotubes as templates. The sequenced histidine-rich peptide molecules were assembled as nanotubes, and the biological recognition of the specific sequence toward Cu lead to efficient Cu coating on the nanotubes. Cu nanocrystals were uniformly coated on the histidine-incorporated nanotubes with high packing density. In addition, the diameter of Cu nanocrystal was controlled between 10 and 30 nm on the nanotube by controlling the conformation of histidine-rich peptide by means of pH changes. Those nanotubes showed significant change in electronic structure by varying the nanocrystal diameter; therefore, this system may be developed to a conductivity-tunable building block for microelectronics and biological sensors. This simple biomineralization method can be applied to fabricate various metallic and semiconductor nanotubes with peptides whose sequences are known to mineralize specific ions.

‣ A unifying approach for food webs, phylogeny, social networks, and statistics

Chiu, Grace S.; Westveld, Anton H.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.71717%
A food web consists of nodes, each consisting of one or more species. The role of each node as predator or prey determines the trophic relations that weave the web. Much effort in trophic food web research is given to understand the connectivity structure, or the nature and degree of dependence among nodes. Social network analysis (SNA) techniques—quantitative methods commonly used in the social sciences to understand network relational structure—have been used for this purpose, although postanalysis effort or biological theory is still required to determine what natural factors contribute to the feeding behavior. Thus, a conventional SNA alone provides limited insight into trophic structure. Here we show that by using novel statistical modeling methodologies to express network links as the random response of within- and internode characteristics (predictors), we gain a much deeper understanding of food web structure and its contributing factors through a unified statistical SNA. We do so for eight empirical food webs: Phylogeny is shown to have nontrivial influence on trophic relations in many webs, and for each web trophic clustering based on feeding activity and on feeding preference can differ substantially. These and other conclusions about network features are purely empirical...