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O problema da troca de mensagens de diferentes tamanhos em redes multi-aglomerados; The complete exchange of messages of different sizes between interconnected clusters using a backbone problem.

Katayama, Fabio Massaaki
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 27/10/2006 PT
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36.53%
Com o aumento no uso de aglomerados e grades de computadores, cresce o interesse no estudo de comunicações entre processadores. Em um computador paralelo dedicado, ou em uma rede local homogênea, o tempo de comunicação é geralmente modelado de forma similar, independente de quais processadores estão se comunicando. Em uma rede onde os links entre os computadores são heterogêneos, computadores mais próximos tendem a apresentar menor latência e maior largura de banda do que computadores distantes. Além disso, a largura de banda agregada é diferente dependendo do número de conexões simultâneas existentes entre dois aglomerados distantes. Neste trabalho estudaremos a troca completa de mensagens de tamanhos diferentes entre aglomerados interligados por backbones. Proporemos um novo algoritmo de comunicação baseado em algoritmos conhecidos, apresentaremos simulações de escalonamentos dos algoritmos estudados para esta rede multi-aglomerado e analisaremos os resultados destas simulações.; The growth in popularity of clusters and computational grids caused an increase in the interest in studying interprocessors communications. The comunication time in a dedicated parallel computer or in a local homogeneous network is modeled in a similar way...

Intrinsic backbone preferences are fully present in blocked amino acids

Avbelj, Franc; Grdadolnik, Simona Golic; Grdadolnik, Joze; Baldwin, Robert L.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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The preferences of amino acid residues for φ,ψ backbone angles vary strikingly among the amino acids, as shown by the backbone angle φ found from the 3J(Hα,HN) coupling constant for short peptides in water. New data for the 3J(Hα,HN) values of blocked amino acids (dipeptides) are given here. Dipeptides exhibit the full range of coupling constants shown by longer peptides such as GGXGG and dipeptides present the simplest system for analyzing backbone preferences. The dipeptide coupling constants are surprisingly close to values computed from the coil library (conformations of residues not in helices and not in sheets). Published coupling constants for GGXGG peptides agree closely with dipeptide values for all nonpolar residues and for some polar residues but not for X = D, N, T, and Y, which are probably affected by polar side chain–backbone interactions in GGXGG peptides. Thus, intrinsic backbone preferences are already determined at the dipeptide level and remain almost unchanged in GGXGG peptides and are strikingly similar in the coil library of conformations from protein structures. The simplest explanation for the backbone preferences is that backbone conformations are strongly affected by electrostatic dipole–dipole interactions in the peptide backbone and by screening of these interactions with water...

Conserved thermodynamic contributions of backbone hydrogen bonds in a protein fold

Wang, Min; Wales, Thomas E.; Fitzgerald, Michael C.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
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Backbone–backbone hydrogen-bonding interactions are a ubiquitous and highly conserved structural feature of proteins that adopt the same fold (i.e., have the same overall backbone topology). This work addresses the question of whether or not this structural conservation is also reflected as a thermodynamic conservation. Reported here is a comparative thermodynamic analysis of backbone hydrogen bonds in two proteins that adopt the same fold but are unrelated at the primary amino acid sequence level. With amide-to-ester bond mutations introduced by total chemical synthesis methods, the thermodynamic consequences of backbone–backbone hydrogen-bond deletions at five different structurally equivalent positions throughout the β-α-α fold of Arc repressor and CopG were assessed. The ester bond-containing analogues all folded into native-like three-dimensional structures that were destabilized from 2.5 to 6.0 kcal/(mol dimer) compared with wild-type controls. Remarkably, the five paired analogues with amide-to-ester bond mutations at structurally equivalent positions were destabilized to exactly the same degree, regardless of the degree to which the mutation site was buried in the structure. The results are interpreted as evidence that the thermodynamics of backbone–backbone hydrogen-bonding interactions in a protein fold are conserved.

Backrub-like backbone simulation recapitulates natural protein conformational variability and improves mutant side-chain prediction

Smith, Colin A.; Kortemme, Tanja
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
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Incorporation of effective backbone sampling into protein simulation and design is an important step in increasing the accuracy of computational protein modeling. Recent analysis of high-resolution crystal structures has suggested a new model, termed backrub, to describe localized, hinge-like alternative backbone and side chain conformations observed in the crystal lattice. The model involves internal backbone rotations about axes between Cα atoms. Based on this observation, we have implemented a backrub-inspired sampling method in the Rosetta structure prediction and design program. We evaluate this model of backbone flexibility using three different tests. First, we show that Rosetta backrub simulations recapitulate the correlation between backbone and side-chain conformations in the high-resolution crystal structures upon which the model was based. As a second test of backrub sampling, we show that backbone flexibility improves the accuracy of predicting point-mutant side chain conformations over fixed backbone rotameric sampling alone. Finally, we show that backrub sampling of triosephosphate isomerase loop 6 can capture the ms/µs oscillation between the open and closed states observed in solution. Our results suggest that backrub sampling captures a sizable fraction of localized conformational changes that occur in natural proteins. Application of this simple model of backbone motions may significantly improve both protein design and atomistic simulations of localized protein flexibility.

TMAO influence on the backbone of proteins: an oligoglycine model

Hu, Char Y.; Lynch, Gillian C.; Kokubo, Hironori; Pettitt, B. Montgomery
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/02/2010 EN
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The study of organic osmolytes has been pivotal in demonstrating the role of solvent effects on the protein backbone in the folding process. Whereas a thermodynamic description of the interactions between the protein backbone and osmolyte has been well defined, the structural analysis of the effect of osmolyte on the protein backbone has been incomplete. Therefore, we have carried out simulations of a peptide backbone model, glycine15 in protecting osmolyte TMAO solution in order to determine the effect of the solution structure on the conformation of the peptide backbone. We demonstrate that the models chosen show that the ensemble of backbone structures shifts towards a more collapsed state in TMAO solution as compared to pure water solution. The collapse is consistent with preferential exclusion of the osmolyte caused by unfavorable interactions between osmolyte and peptide backbone. The exclusion is due to strong triplet correlations of osmolyte, water, and peptide backbone. This provides a clear mechanism demonstrating that even a modest concentration of TMAO forces the protein backbone to adopt a more collapsed structure in the absence of sidechain effects.

Retrieving Backbone String Neighbors Provides Insights Into Structural Modeling of Membrane Proteins*

Sun, Jiang-Ming; Li, Tong-Hua; Cong, Pei-Sheng; Tang, Sheng-Nan; Xiong, Wen-Wei
Fonte: The American Society for Biochemistry and Molecular Biology Publicador: The American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
EN
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26.96%
Identification of protein structural neighbors to a query is fundamental in structure and function prediction. Here we present BS-align, a systematic method to retrieve backbone string neighbors from primary sequences as templates for protein modeling. The backbone conformation of a protein is represented by the backbone string, as defined in Ramachandran space. The backbone string of a query can be accurately predicted by two innovative technologies: a knowledge-driven sequence alignment and encoding of a backbone string element profile. Then, the predicted backbone string is employed to align against a backbone string database and retrieve a set of backbone string neighbors. The backbone string neighbors were shown to be close to native structures of query proteins. BS-align was successfully employed to predict models of 10 membrane proteins with lengths ranging between 229 and 595 residues, and whose high-resolution structural determinations were difficult to elucidate both by experiment and prediction. The obtained TM-scores and root mean square deviations of the models confirmed that the models based on the backbone string neighbors retrieved by the BS-align were very close to the native membrane structures although the query and the neighbor shared a very low sequence identity. The backbone string system represents a new road for the prediction of protein structure from sequence...

Dead-End Elimination with Perturbations (“DEEPer”): A provable protein design algorithm with continuous sidechain and backbone flexibility

Hallen, Mark A.; Keedy, Daniel A.; Donald, Bruce R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
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Computational protein and drug design generally require accurate modeling of protein conformations. This modeling typically starts with an experimentally-determined protein structure and considers possible conformational changes due to mutations or new ligands. The DEE/A* algorithm provably finds the GMEC (global minimum-energy conformation) of a protein assuming the backbone does not move and the sidechains take on conformations from a set of discrete, experimentally-observed conformations called rotamers. DEE/A* can efficiently find the overall GMEC for exponentially many mutant sequences. Previous improvements to DEE/A* include modeling ensembles of sidechain conformations and either continuous sidechain or backbone flexibility. We present a new algorithm, DEEPer (Dead-End Elimination with Perturbations), that combines these advantages and can also handle much more extensive backbone flexibility and backbone ensembles. DEEPer provably finds the GMEC or, if desired by the user, all conformations and sequences within a specified energy window of the GMEC. It includes the new abilities to handle arbitrarily large backbone perturbations and to generate ensembles of backbone conformations. It also incorporates the shear, an experimentally-observed local backbone motion never before used in design. Additionally...

A simple model of backbone flexibility improves modeling of side-chain conformational variability

Friedland, Gregory D.; Linares, Anthony J.; Smith, Colin A.; Kortemme, Tanja
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
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The considerable flexibility of side-chains in folded proteins is important for protein stability and function, and may play a role in mediating pathways of energetic connectivity between allosteric sites. While sampling side-chain degrees of freedom has been an integral part of several successful computational protein design methods, the predictions of these approaches have not been directly compared to experimental measurements of side-chain motional amplitudes. In addition, protein design methods generally keep the backbone fixed, an approximation that may substantially limit the ability to accurately model side-chain flexibility. Here we describe a Monte Carlo approach to modeling side-chain conformational variability and validate our method against a large dataset of methyl relaxation order parameters derived from Nuclear Magnetic Resonance experiments (17 proteins and a total of 530 data points). We also evaluate a model of backbone flexibility based on Backrub motions, a type of conformational change frequently observed in ultra-high resolution X-ray structures that accounts for correlated side-chain backbone movements. The fixed-backbone model performs reasonably well with an overall rmsd between computed and predicted side-chain order parameters of 0.26. Notably...

Changing the topology of protein backbone: the effect of backbone cyclization on the structure and dynamics of a SH3 domain

Schumann, Frank H.; Varadan, Ranjani; Tayakuniyil, Praveen P.; Grossman, Jennifer H.; Camarero, Julio A.; Fushman, David
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 08/04/2015 EN
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26.93%
Understanding of the effects of the backbone cyclization on the structure and dynamics of a protein is essential for using protein topology engineering to alter protein stability and function. Here we have determined, for the first time, the structure and dynamics of the linear and various circular constructs of the N-SH3 domain from protein c-Crk. These constructs differ in the length and amino acid composition of the cyclization region. The backbone cyclization was carried out using intein-mediated intramolecular chemical ligation between the juxtaposed N- and the C-termini. The structure and backbone dynamics studies were performed using solution NMR. Our data suggest that the backbone cyclization has little effect on the overall three-dimensional structure of the SH3 domain: besides the termini, only minor structural changes were found in the proximity of the cyclization region. In contrast to the structure, backbone dynamics are significantly affected by the cyclization. On the subnanosecond time scale, the backbone of all circular constructs on average appears more rigid than that of the linear SH3 domain; this effect is observed over the entire backbone and is not limited to the cyclization site. The backbone mobility of the circular constructs becomes less restricted with increasing length of the circularization loop. In addition...

Uma proposta para a provisão de QoS em redes backbone UMTS

Alecrim, Paulo Dias de
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Dissertação
POR
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Com o crescimento da demanda das aplicações multimídia na Internet e com os atuais backbones de alta capacidade, espera-se que as redes backbone UMTS suportem diferentes aplicações com requisitos de QoS, principalmente aquelas sensíveis a retardos, perdas e jitter. Entretanto, as aplicações de tempo real exigem mecanismos apropriados para garantir QoS de acordo com suas características específicas. Neste trabalho propõe-se a utilização de um mecanismo baseada no modelo DiffServ, que classificará e tratará cada pacote de acordo com as necessidades estabelecidas previamente por suas aplicações. Tal proposta provê um tratamento diferenciado ao tráfego de diversos fluxos na rede. Os resultados obtidos a partir de modelagem e simulação demonstraram que a utilização do mecanismo proposto trata as classes de tráfego UMTS de forma diferenciada, oferecendo um nível de QoS satisfatório mesmo em condições de mobilidade dos usuários. ______________________________________________________________________________ ABSTRACT; With the growth of the demand of multimedia applications in the Internet and with the current backbones, it is expected that UMTS backbones support different applications with QoS requirements, mainly those which are sensitive to delays...

Backbone Colouring of Graphs

Golestanian, Arnoosh
Fonte: Brock University Publicador: Brock University
Tipo: Electronic Thesis or Dissertation
ENG
Relevância na Pesquisa
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Consider an undirected graph G and a subgraph of G, H. A q-backbone k-colouring of (G,H) is a mapping f: V(G) {1, 2, ..., k} such that G is properly coloured and for each edge of H, the colours of its endpoints differ by at least q. The minimum number k for which there is a backbone k-colouring of (G,H) is the backbone chromatic number, BBCq(G,H). It has been proved that backbone k-colouring of (G,T) is at most 4 if G is a connected C4-free planar graph or non-bipartite C5-free planar graph or Cj-free, j∈{6,7,8} planar graph without adjacent triangles. In this thesis we improve the results mentioned above and prove that 2-backbone k-colouring of any connected planar graphs without adjacent triangles is at most 4 by using a discharging method. In the second part of this thesis we further improve these results by proving that for any graph G with χ(G) ≥ 4, BBC(G,T) = χ(G). In fact, we prove the stronger result that a backbone tree T in G exists, such that ∀ uv ∈ T, |f(u)-f(v)|=2 or |f(u)-f(v)| ≥ k-2, k = χ(G). For the case that G is a planar graph, according to Four Colour Theorem, χ(G) = 4; so, BBC(G,T) = 4.

Broadband for Africa : Developing Backbone Communications Networks

Williams, Mark D. J.
Fonte: World Bank Publicador: World Bank
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Many countries in Sub-Saharan Africa see information and communication technology (ICT) as a necessary foundation for long-term economic development. While the region has been very successful in increasing access to basic voice communications, there has been no comparable improvement in broadband connectivity. In fact, the broadband access gap between Sub-Saharan Africa and the rest of the world is getting wider just as the gap in basic voice communications is getting smaller. Increasing access to broadband connectivity is therefore emerging as a high priority for policy makers across the continent. This book begins with a brief review of the ICT market and considers the extent of demand for broadband and the ICT services that high-capacity backbone networks make possible. This is followed by a review of the existing coverage of backbone networks in the region, a discussion of how this compares with other parts of the world, and an analysis of the possible explanations for the current pattern of network development. Finally...

Small-Time Scaling Behavior of Internet Backbone Traffic

Ribeiro, Vinay Joseph; Zhang, Zhi-Li; Moon, Sue; Diot, Christophe; Ribeiro, Vinay Joseph; Zhang, Zhi-Li; Moon, Sue; Diot, Christophe
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Journal Paper; We perform an extensive wavelet analysis of Internet backbone traffic signals to observe and understand the causes of small-time (sub-seconds) scaling phenomena present in them. We observe that for a majority of the traffic traces, the (second-order) scaling exponents at small time scales (1ms - 100ms) are fairly close to 0.5, indicating that traffic fluctuations at these time scales are (nearly) uncorrelated. Some traces, however, do exhibit moderately large scaling exponents (approximately 0.7) at small time scales. In addition, the traces manifest mostly monofractal behaviors at small time scales. To identify the network causes of the observed scaling behavior, we analyze the flow composition of the traffic along two dimensions -- flow size and flow density. Our study points to the dense flows (i.e., flows with bursts of densely clustered packets) as the correlation-causing factor in small time scales, and reveals that the traffic composition in terms of proportions of dense vs. sparse flows plays a major role in influencing the small-time scalings of aggregate traffic. Since queuing inside routers is strongly influenced by traffic fluctuations at small time-scales, our observations and results have significant implications in networking modeling...

Small-time scaling behaviors of Internet backbone traffic: An empirical study

Zhang, Zhi-Li; Ribeiro, Vinay Joseph; Moon, Sue; Diot, Christophe; Zhang, Zhi-Li; Ribeiro, Vinay Joseph; Moon, Sue; Diot, Christophe
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Conference paper
ENG
Relevância na Pesquisa
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Conference Paper; We study the small-time (sub-seconds) scaling behaviors of Internet backbone traffic, based on traces collected from OC3/12/48 links in a tier-1 ISP. We observe that for a majority of these traces, the (second-order) scaling exponents at small time scales (1ms - 100ms) are fairly close to 0.5, indicating that traffic fluctuations at these time scales are (nearly) uncorrelated. In addition, the traces manifest mostly monofractal behaviors at small time scales. The objective of the paper is to understand the potential causes or factors that influence the small-time scalings of Internet backbone traffic via empirical data analysis. We analyze the traffic composition of the traces along two dimensions â flow size and flow density. Our study uncovers dense flows (i.e., flows with bursts of densely clustered packets) as the correlation-causing factor in small time scales, and reveals that the traffic composition in terms of proportions of dense vs. sparse flows plays a major role in influecing the small-time scalings of aggregate traffic.

Aplicações single-page: caso de implementação com Backbone.js

Vitorino, Bruno
Fonte: Universidade Aberta de Portugal Publicador: Universidade Aberta de Portugal
Tipo: Trabalho em Andamento
Publicado em /09/2015 POR
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Trabalho apresentado no Mestrado em Tecnologias e Sistemas Informáticos Web, com uma pequena introdução ao conceito de aplicações Single-page e um exemplo de implementação utilizando a framework Backbone.js

Backbone Fragility and the Local Search Cost Peak

Gent, I. P.; Singer, J.; Smaill, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/06/2011
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26.97%
The local search algorithm WSat is one of the most successful algorithms for solving the satisfiability (SAT) problem. It is notably effective at solving hard Random 3-SAT instances near the so-called `satisfiability threshold', but still shows a peak in search cost near the threshold and large variations in cost over different instances. We make a number of significant contributions to the analysis of WSat on high-cost random instances, using the recently-introduced concept of the backbone of a SAT instance. The backbone is the set of literals which are entailed by an instance. We find that the number of solutions predicts the cost well for small-backbone instances but is much less relevant for the large-backbone instances which appear near the threshold and dominate in the overconstrained region. We show a very strong correlation between search cost and the Hamming distance to the nearest solution early in WSat's search. This pattern leads us to introduce a measure of the backbone fragility of an instance, which indicates how persistent the backbone is as clauses are removed. We propose that high-cost random instances for local search are those with very large backbones which are also backbone-fragile. We suggest that the decay in cost beyond the satisfiability threshold is due to increasing backbone robustness (the opposite of backbone fragility). Our hypothesis makes three correct predictions. First...

Estimating Market Power in the Internet Backbone Using Band-X data

Giovannetti, Emanuele; Ristuccia, Cristiano A.
Fonte: Universidade de Cambridge Publicador: Universidade de Cambridge
Tipo: Trabalho em Andamento Formato: 417870 bytes; application/pdf; application/pdf
EN_GB
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Recent industry studies found the Internet backbone industry competitive. In our paper we explore a novel route to monitor for market power using prices and quality data from Band-X. First we test the hypothesis that Europe is a connectivity market on its own, unchallenged by the US and then, by using a Panel data Regression, we find that these markets are not very competitive since brand effects play a major role because price variations are only marginally affected by qualitative dimensions. More worryingly we find that companies with high prices are often able to supply an inferior quality I.P. transit.

RNA Backbone Rotamers and Chiropraxis

Murray, Laura Weston
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação Formato: 17902885 bytes; application/pdf
Publicado em 25/07/2007 EN_US
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RNA backbone is biologically important with many roles in reactions and interactions, but has historically been a challenge in structural determination. It has many atoms and torsions to place, and often there is less data on it than one might wish. This problem leads to both random and systematic error, producing noise in an already high-dimensional and complex distribution to further complicate data-driven analysis. With the advent of the ribosomal subunit structures published in 2000, large RNA structures at good resolution, it became possible to apply the Richardson laboratory's quality-filtering, visualization, and analysis techniques to RNA and develop new tools for RNA as well. A first set of 42 RNA backbone rotamers was identified, developed, and published in 2003; it has since been thoroughly overhauled in conjunction with the backbone group of the RNA Ontology Consortium to combine the strengths of different approaches, incorporate new data, and produce a consensus set of 46 conformers. Meanwhile, extensive work has taken place on developing validation and remodeling tools to correct and improve existing structures as well as to assist in initial fitting. The use of base-phosphate perpendicular distances to identify sugar pucker has proven very useful in both hand-refitting and the semi-automated process of using RNABC (RNA Backbone Correction)...

Local Motion And Local Accuracy In Protein Backbone

Davis, Ian Wheeler
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação Formato: 18399336 bytes; 333 pages.; application/pdf
EN_US
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Proteins are chemically simple molecules, being unbranched polymers of uncomplicated organic compounds. Nonetheless, they fold up into a dazzling variety of complex and beautiful configurations with a dizzying array of structural, regulatory, and catalytic functions. Despite great progress, we still have very limited ability to predict the folded conformation of an amino acid sequence, and limited understanding of its dynamics and motions. Thus, this work presents a quartet of interrelated studies that address some aspects of the detailed local conformations and motions of protein backbone. First, I used a density-dependent smoothing algorithm and a high-quality, B-filtered data set to construct highly accurate conformational distributions for protein backbone (Ramachandran plots) and sidechains (rotamers). These distributions are the most accurate and restrictive produced to date, with improved discrimination between rare-but-real conformations and artifactual ones. Second, I analyzed hundreds of alternate conformations in atomic resolution crystal structures, and discovered that dramatic conformational change in a protein sidechain is often coupled to a subtle but very common mode of conformational change in its backbone -- the backrub motion. Examination of other biophysical data further supports the ubiquity of this motion. Third...

RNA Backbone Validation, Correction, and Implications for RNA-Protein Interfaces

Kapral, Gary Joseph
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2013
Relevância na Pesquisa
26.91%

RNA is the molecular workhorse of nature, capable of doing many cellular tasks, from genetic data storage and regulation, to enzymatic synthesis--even to the point of self-catalyzing its own replication. While RNA can act as a catalyst on its own, as in the hammerhead ribozyme, the added efficiency of proteins is often a necessity; the ribosome--the large ribozyme responsible for peptide chain formation, is aided by proteins which ensure correct assembly and structural stability. These complexes of RNA and proteins feature in many essential cellular processes, including the RISC silencing complex and in the spliceosome. Despite its enormous utility, structural determination of RNA is notoriously difficult--particularly in the backbone, since a nucleotide standardly has 12 torsion angles (including χ) and 12 non-hydrogen atoms, compared to 4 torsions (including χ1) and 4 non-H atoms in a typical amino acid. The abundance of backbone atoms, their conformational flexibility, and experimental resolution limitations often result in systematic errors that can have a significant impact on the interpretation. False trails due to structural errors can lead to significant loss of time and effort, especially with such high-profile complexes as the ribosome and the RISC complex.

My research has focused on harnessing the recently discovered ribosome structures and the Richardsons' RNA dataset to find trends in RNA backbone conformations and motifs that were then used to develop structural validation techniques and provide improved diagnosis and correction techniques for RNA backbone. Methods for fixing RNA structure have been developed for both NMR and X-ray crystallography. For NMR structures...