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Influência do tamanho das bases ósseas apicais no apinhamento dentário; Relationship of apical base length and dental crowding

Murillo-Goizueta, Oscar Edwin Francisco
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 26/01/2009 PT
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27.27%
A influencia de diversos fatores, principalmente no apinhamento dentário antero-inferior, vem sendo estudada desde muito tempo atras. Entretanto, a influencia do comprimento das bases apicais sobre o apinhamento dentario ainda nao foi esclarecida. Como existem evidencias na literatura de que esse fator pode influenciar o apinhamento dentario, resolveu-se desenvolver este trabalho para investigar a relacao entre comprimentos de bases apicais e apinhamento dentário superior e inferior na ma oclusao de Classe II completa. Um total de 80 documentacoes de pacientes ortodonticos retrospectivos, 47 homens e 33 mulheres com ma oclusao de Classe II completa foram divididas em 2 grupos segundo a discrepancia do perimetro do arco ou apinhamento inferior. O grupo 1, constituído por 25 pacientes com apinhamento inferior 3mm e com uma idade media de 12,81 anos; e o grupo 2, formado por 55 pacientes com apinhamento inferior < 3mm e com uma idade media de 13,33 anos. Os comprimentos das bases apicais da maxila e da mandibula e as discrepancias do perimetro dos arcos foram medidos nos cefalogramas e nos modelos de estudo iniciais, respectivamente. Os comprimentos das bases apicais e o apinhamento dentario foram comparados entre os grupos pelo teste t e tambem foram realizadas correlacoes entre os comprimentos das bases e o apinhamento para cada arco dentario. Os resultados mostraram que o grupo com maior apinhamento dentario teve comprimentos de bases apicais significantemente menores. Tambem foi encontrada uma correlacao negativa significante entre o comprimento das bases osseas e o apinhamento dentario na ma oclusao de Classe II completa.; The influence of many factors on dental crowding has been studied since long time ago...

Avaliação da correlação da recidiva da sobressaliência e da sobremordida com a recidiva do apinhamento anterior em casos tratados com extrações; Evaluation of the correlation of the overjet and overbite relapse with the relapse of anterior crowding in extraction cases

Oliveira, Ricardo Cesar Gobbi de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 02/03/2011 PT
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27.34%
Tendo em vista a imprevisibilidade da estabilidade oclusal pós correção ortodôntica, este estudo objetivou correlacionar a recidiva da sobremordida e da sobressaliência com a recidiva do apinhamento ântero-superior e ântero-inferior, em casos com má oclusão de Classe I e Classe II de Angle, tratados ortodonticamente com extração de 4 pré-molares, tratados pela técnica Edgewise. Para isso, foram selecionados 40 pacientes (20 do gênero feminino e 20 do gênero masculino), 25 pacientes portadores de má oclusão de Classe I e 15 de Classe II de Angle, com idade média inicial de 13,01 anos, que foram tratados por um tempo médio de 2,15 anos, e avaliados na fase pós-contenção após um período médio de 5,43 anos. Todos os pacientes apresentavam pelo menos 3 mm de sobremordida e 4mm de sobressaliência ao início do tratamento ortodôntico. Foram utilizados os modelos de gesso das fases do início do tratamento (T1), final de tratamento (T2) e da fase pós-contenção, em média 5 anos após o término do tratamento (T3) de todos os casos selecionados para que fossem quantificadas as recidivas dessas duas variáveis, assim como a recidiva do apinhamento anterior. Utilizou-se a análise de variância a um critério de seleção...

Crowding and surround suppression: Not to be confused

Petrov, Yury; Popple, Ariella V.; McKee, Suzanne P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/04/2007 EN
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Crowding and surround suppression share many similarities, which suggests the possibility of a common mechanism. Despite decades of research, there has been little effort to compare the two phenomena in a consistent fashion. A recent study by D. M. Levi, S. Hariharan, and S. A. Klein (2002) argues that the two are unrelated because crowding effects can be much stronger than suppression effects. Here we report experiments in which the same Gabor target was used both for orientation identification (crowding) and contrast detection (suppression) tasks. In agreement with early crowding studies (e. g., H. Bouma, 1973) we found, that an outward mask is much more effective than an inward mask for the orientation identification task. Notably, no such anisotropy was observed for the contrast detection task, commonly used to measure surround suppression. The anisotropic masking, which defines crowding, is observed only at fine scales (roughly within an octave of the acuity limit), whereas surround suppression is observed at all scales. Our results demonstrate that surround suppression and crowding are indeed two distinct phenomena. We used this characteristic anisotropy to show that a popular crowding paradigm in which target contrast is varied to measure crowding is confounding it with surround suppression. Surround suppression apparently dominates at low contrasts...

The nature of letter crowding as revealed by first- and second-order classification images

Nandy, Anirvan S.; Tjan, Bosco S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 07/02/2007 EN
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Visual crowding refers to the marked inability to identify an otherwise perfectly identifiable object when it is flanked by other objects. Crowding places a significant limit on form vision in the visual periphery; its mechanism is, however, unknown. Building on the method of signal-clamped classification images (Tjan & Nandy, 2006), we developed a series of first- and second-order classification-image techniques to investigate the nature of crowding without presupposing any model of crowding. Using an “o” versus “x” letter-identification task, we found that (1) crowding significantly reduced the contrast of first-order classification images, although it did not alter the shape of the classification images; (2) response errors during crowding were strongly correlated with the spatial structures of the flankers that resembled those of the erroneously perceived targets; (3) crowding had no systematic effect on intrinsic spatial uncertainty of an observer nor did it suppress feature detection; and (4) analysis of the second-order classification images revealed that crowding reduced the amount of valid features used by the visual system and, at the same time, increased the amount of invalid features used. Our findings strongly support the feature-mislocalization or source-confusion hypothesis as one of the proximal contributors of crowding. Our data also agree with the inappropriate feature-integration account with the requirement that feature integration be a competitive process. However...

Holistic crowding of Mooney faces

Farzin, Faraz; Rivera, Susan M.; Whitney, David
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 29/06/2009 EN
Relevância na Pesquisa
27.27%
An object or feature is generally more difficult to identify when other objects are presented nearby, an effect referred to as crowding. Here, we used Mooney faces to examine whether crowding can also occur within and between holistic face representations (C. M. Mooney, 1957). Mooney faces are ideal stimuli for this test because no cues exist to distinguish facial features in a Mooney face; to find any facial feature, such as an eye or a nose, one must first holistically perceive the image as a face. Through a series of six experiments we tested the effect of crowding on Mooney face recognition. Our results demonstrate crowding between and within Mooney faces and fulfill the diagnostic criteria for crowding, including eccentricity dependence and lack of crowding in the fovea, critical flanker spacing consistent with less than half the eccentricity of the target, and inner-outer flanker asymmetry. Further, our results show that recognition of an upright Mooney face is more strongly impaired by upright Mooney face flankers than inverted ones. Taken together, these results suggest crowding can occur selectively between high-level representations of faces and that crowding must occur at multiple levels in the visual system.

Effects of Macromolecular Crowding on Protein Conformational Changes

Dong, Hao; Qin, Sanbo; Zhou, Huan-Xiang
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.32%
Many protein functions can be directly linked to conformational changes. Inside cells, the equilibria and transition rates between different conformations may be affected by macromolecular crowding. We have recently developed a new approach for modeling crowding effects, which enables an atomistic representation of “test” proteins. Here this approach is applied to study how crowding affects the equilibria and transition rates between open and closed conformations of seven proteins: yeast protein disulfide isomerase (yPDI), adenylate kinase (AdK), orotidine phosphate decarboxylase (ODCase), Trp repressor (TrpR), hemoglobin, DNA β-glucosyltransferase, and Ap4A hydrolase. For each protein, molecular dynamics simulations of the open and closed states are separately run. Representative open and closed conformations are then used to calculate the crowding-induced changes in chemical potential for the two states. The difference in chemical-potential change between the two states finally predicts the effects of crowding on the population ratio of the two states. Crowding is found to reduce the open population to various extents. In the presence of crowders with a 15 Å radius and occupying 35% of volume, the open-to-closed population ratios of yPDI...

Macromolecular crowding remodels the energy landscape of a protein by favoring a more compact unfolded state

Hong, Jiang; Gierasch, Lila M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 04/08/2010 EN
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27.3%
The interior of cells is highly crowded with macromolecules, which impacts all physiological processes. To explore how macromolecular crowding may influence cellular protein folding, we interrogated the folding landscape of a model β-rich protein, cellular retinoic acid-binding protein I (CRABP I), in the presence of an inert crowding agent (Ficoll 70). Urea titrations revealed a crowding-induced change in the water-accessible polar amide surface of its denatured state, based on an observed ca. 15% decrease in the m-value (the change in unfolding free energy with respect to urea concentration), and the effect of crowding on the equilibrium stability of CRABP I was less than our experimental error (i.e., ≤1.2 kcal/mol). Consequently, we directly probed the effect of crowding on the denatured state of CRABP I by measuring side chain accessibility using iodide quenching of tryptophan fluorescence and chemical modification of cysteines. We observed that the urea-denatured state is more compact under crowded conditions, and the observed extent of reduction of the m value by crowding agent is fully consistent with the extent of reduction of the accessibility of the Trp and Cys probes, suggesting a random and nonspecific compaction of the unfolded state. The thermodynamic consequences of crowding-induced compaction are discussed. In addition...

Saccadic selection and crowding in visual search: stronger lateral masking leads to shorter search times

de Vries, Jelmer P.; Hooge, Ignace T. C.; Wiering, Marco A.; Verstraten, Frans A. J.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
27.3%
We investigated the role of crowding in saccadic selection during visual search. To guide eye movements, often information from the visual periphery is used. Crowding is known to deteriorate the quality of peripheral information. In four search experiments, we studied the role of crowding, by accompanying individual search elements by flankers. Varying the difference between target and flankers allowed us to manipulate crowding strength throughout the stimulus. We found that eye movements are biased toward areas with little crowding for conditions where a target could be discriminated peripherally. Interestingly, for conditions in which the target could not be discriminated peripherally, this bias reversed to areas with strong crowding. This led to shorter search times for a target presented in areas with stronger crowding, compared to a target presented in areas with less crowding. These findings suggest a dual role for crowding in visual search. The presence of flankers similar to the target deteriorates the quality of the peripheral target signal but can also attract eye movements, as more potential targets are present over the area.

Ideal observer analysis of crowding and the reduction of crowding through learning

Sun, Gerald J.; Chung, Susana T. L.; Tjan, Bosco S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/05/2010 EN
Relevância na Pesquisa
27.3%
Crowding is a prominent phenomenon in peripheral vision where nearby objects impede one’s ability to identify a target of interest. The precise mechanism of crowding is not known. We used ideal observer analysis and a noise-masking paradigm to identify the functional mechanism of crowding. We tested letter identification in the periphery with and without flanking letters and found that crowding increases equivalent input noise and decreases sampling efficiency. Crowding effectively causes the signal from the target to be noisier and at the same time reduces the visual system’s ability to make use of a noisy signal. After practicing identification of flanked letters without noise in the periphery for 6 days, subjects’ performance for identifying flanked letters improved (reduction of crowding). Across subjects, the improvement was attributable to either a decrease in crowding-induced equivalent input noise or an increase in sampling efficiency, but seldom both. This pattern of results is consistent with a simple model whereby learning reduces crowding by adjusting the spatial extent of a perceptual window used to gather relevant input features. Following learning, subjects with inappropriately large windows reduced their window sizes; while subjects with inappropriately small windows increased their window sizes. The improvement in equivalent input noise and sampling efficiency persists for at least 6 months.

Perceived Positions Determine Crowding

Maus, Gerrit W.; Fischer, Jason; Whitney, David
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 24/05/2011 EN
Relevância na Pesquisa
27.3%
Crowding is a fundamental bottleneck in object recognition. In crowding, an object in the periphery becomes unrecognizable when surrounded by clutter or distractor objects. Crowding depends on the positions of target and distractors, both their eccentricity and their relative spacing. In all previous studies, position has been expressed in terms of retinal position. However, in a number of situations retinal and perceived positions can be dissociated. Does retinal or perceived position determine the magnitude of crowding? Here observers performed an orientation judgment on a target Gabor patch surrounded by distractors that drifted toward or away from the target, causing an illusory motion-induced position shift. Distractors in identical physical positions led to worse performance when they drifted towards the target (appearing closer) versus away from the target (appearing further). This difference in crowding corresponded to the difference in perceived positions. Further, the perceptual mislocalization was necessary for the change in crowding, and both the mislocalization and crowding scaled with drift speed. The results show that crowding occurs after perceived positions have been assigned by the visual system. Crowding does not operate in a purely retinal coordinate system; perceived positions need to be taken into account.

Crowding follows the binding of relative position and orientation

Greenwood, John A.; Bex, Peter J.; Dakin, Steven C.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 21/03/2012 EN
Relevância na Pesquisa
27.34%
Crowding–the deleterious influence of clutter on object recognition–disrupts the identification of visual features as diverse as orientation, motion, and color. It is unclear whether this occurs via independent feature-specific crowding processes (preceding the feature binding process) or via a singular (late) mechanism tuned for combined features. To examine the relationship between feature binding and crowding, we measured interactions between the crowding of relative position and orientation. Stimuli were a target cross and two flanker crosses (each composed of two near-orthogonal lines), 15 degrees in the periphery. Observers judged either the orientation (clockwise/counterclockwise) of the near-horizontal target line, its position (up/down relative to the stimulus center), or both. For single-feature judgments, crowding affected position and orientation similarly: thresholds were elevated and responses biased in a manner suggesting that the target appeared more like the flankers. These effects were tuned for orientation, with near-orthogonal elements producing little crowding. This tuning allowed us to separate the predictions of independent (feature specific) and combined (singular) models: for an independent model, reduced crowding for one feature has no effect on crowding for other features...

Grouping and Crowding Affect Target Appearance over Different Spatial Scales

Sayim, Bilge; Cavanagh, Patrick
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 13/08/2013 EN
Relevância na Pesquisa
27.3%
Crowding is the impairment of peripheral target perception by nearby flankers. A number of recent studies have shown that crowding shares many features with grouping. Here, we investigate whether effects of crowding and grouping on target perception are related by asking whether they operate over the same spatial scale. A target letter T had two sets of flanking Ts of varying orientations. The first set was presented close to the target, yielding strong crowding. The second set was either close enough to cause crowding on their own or too far to cause crowding on their own. The Ts of the second set had the same orientation that either matched the target’s orientation (Grouped condition) or not (Ungrouped condition). In Experiment 1, the Grouped flankers reduced crowding independently of their distance from the target, suggesting that grouping operated over larger distances than crowding. In Experiments 2 and 3 we found that grouping did not affect sensitivity but produced a strong bias to report that the grouped orientation was present at the target location whether or not it was. Finally, we investigated whether this bias was a response or perceptual bias, rejecting the former in favor of a perceptual grouping explanation. We suggest that the effect of grouping is to assimilate the target to the identity of surrounding flankers when they are all the same...

The Effect of Macromolecular Crowding on the Electrostatic Component of Barnase–Barstar Binding: A Computational, Implicit Solvent-Based Study

Qi, Helena W.; Nakka, Priyanka; Chen, Connie; Radhakrishnan, Mala L.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 10/06/2014 EN
Relevância na Pesquisa
27.3%
Macromolecular crowding within the cell can impact both protein folding and binding. Earlier models of cellular crowding focused on the excluded volume, entropic effect of crowding agents, which generally favors compact protein states. Recently, other effects of crowding have been explored, including enthalpically-related crowder–protein interactions and changes in solvation properties. In this work, we explore the effects of macromolecular crowding on the electrostatic desolvation and solvent-screened interaction components of protein–protein binding. Our simple model enables us to focus exclusively on the electrostatic effects of water depletion on protein binding due to crowding, providing us with the ability to systematically analyze and quantify these potentially intuitive effects. We use the barnase–barstar complex as a model system and randomly placed, uncharged spheres within implicit solvent to model crowding in an aqueous environment. On average, we find that the desolvation free energy penalties incurred by partners upon binding are lowered in a crowded environment and solvent-screened interactions are amplified. At a constant crowder density (fraction of total available volume occupied by crowders), this effect generally increases as the radius of model crowders decreases...

The hierarchical sparse selection model of visual crowding

Chaney, Wesley; Fischer, Jason; Whitney, David
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
Publicado em 25/09/2014 EN
Relevância na Pesquisa
27.3%
Because the environment is cluttered, objects rarely appear in isolation. The visual system must therefore attentionally select behaviorally relevant objects from among many irrelevant ones. A limit on our ability to select individual objects is revealed by the phenomenon of visual crowding: an object seen in the periphery, easily recognized in isolation, can become impossible to identify when surrounded by other, similar objects. The neural basis of crowding is hotly debated: while prevailing theories hold that crowded information is irrecoverable – destroyed due to over-integration in early stage visual processing – recent evidence demonstrates otherwise. Crowding can occur between high-level, configural object representations, and crowded objects can contribute with high precision to judgments about the “gist” of a group of objects, even when they are individually unrecognizable. While existing models can account for the basic diagnostic criteria of crowding (e.g., specific critical spacing, spatial anisotropies, and temporal tuning), no present model explains how crowding can operate simultaneously at multiple levels in the visual processing hierarchy, including at the level of whole objects. Here, we present a new model of visual crowding—the hierarchical sparse selection (HSS) model...

Crowding by a repeating pattern

Rosen, Sarah; Pelli, Denis G.
Fonte: The Association for Research in Vision and Ophthalmology Publicador: The Association for Research in Vision and Ophthalmology
Tipo: Artigo de Revista Científica
Publicado em 18/05/2015 EN
Relevância na Pesquisa
27.3%
Theinability to recognize a peripheral target among flankers is called crowding. For a foveal target, crowding can be distinguished from overlap masking by its sparing of detection, linear scaling with eccentricity, and invariance with target size.Crowding depends on the proximity and similarity of the flankers to the target. Flankers that are far from or dissimilar to the target do not crowd it. On a gray page, text whose neighboring letters have different colors, alternately black and white, has enough dissimilarity that it might escape crowding. Since reading speed is normally limited by crowding, escape from crowding should allow faster reading. Yet reading speed is unchanged (Chung & Mansfield, 2009). Why? A recent vernier study found that using alternating-color flankers produces strong crowding (Manassi, Sayim, & Herzog, 2012). Might that effect occur with letters and reading? Critical spacing is the minimum center-to-center target–flanker spacing needed to correctly identify the target. We measure it for a target letter surrounded by several equidistant flanker letters of the same polarity, opposite polarity, or mixed polarity: alternately white and black. We find strong crowding in the alternating condition, even though each flanker letter is beyond its own critical spacing (as measured in a separate condition). Thus a periodic repeating pattern can produce crowding even when the individual elements do not. Further...

Heterogeneous Tiebout communities with private production and anonymous crowding

Luque, Jaime
Fonte: Universidade Carlos III de Madrid Publicador: Universidade Carlos III de Madrid
Tipo: Trabalho em Andamento Formato: text/plain; application/pdf
Publicado em /09/2011 ENG
Relevância na Pesquisa
36.84%
his paper examines, in the context of a multiple types of consumers, a set of necessary and sufficient conditions under which equilibrium and optimum exist, and involve mixing types of consumers in jurisdictions. Pricing includes visa permits for entry. Following Berglas (1976), we assume anonymous crowding and complementarities in production. For a large economy, we prove existence of equilibrium and the first and second welfare theorems. Our simultaneous optimization approach provides a new technique for showing existence of equilibrium in local public good economies with local production and a continuum of agents.; Financial support of FCT and INOVA (Portugal), the European Science Foundation (through the activity “Public Goods, Public Projects and Externalities”), and the Spanish Ministry of Education and Science under the grant SEJ2008-03516.

Crowding, grouping, and object recognition: A matter of appearance

Herzog, Michael H.; Sayim, Bilge; Chicherov, Vitaly; Manassi, Mauro
Fonte: The Association for Research in Vision and Ophthalmology Publicador: The Association for Research in Vision and Ophthalmology
Tipo: Artigo de Revista Científica
Publicado em 05/05/2015 EN
Relevância na Pesquisa
27.3%
In crowding, the perception of a target strongly deteriorates when neighboring elements are presented. Crowding is usually assumed to have the following characteristics. (a) Crowding is determined only by nearby elements within a restricted region around the target (Bouma's law). (b) Increasing the number of flankers can only deteriorate performance. (c) Target-flanker interference is feature-specific. These characteristics are usually explained by pooling models, which are well in the spirit of classic models of object recognition. In this review, we summarize recent findings showing that crowding is not determined by the above characteristics, thus, challenging most models of crowding. We propose that the spatial configuration across the entire visual field determines crowding. Only when one understands how all elements of a visual scene group with each other, can one determine crowding strength. We put forward the hypothesis that appearance (i.e., how stimuli look) is a good predictor for crowding, because both crowding and appearance reflect the output of recurrent processing rather than interactions during the initial phase of visual processing.

Macromolecular Crowding Modulates Folding Mechanism of α/β Protein Apoflavodoxin

Homouz, Dirar; Stagg, Loren; Wittung-Stafshede, Pernilla; Cheung, Margaret S.
Fonte: The Biophysical Society Publicador: The Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em 21/01/2009 EN
Relevância na Pesquisa
27.32%
Protein dynamics in cells may be different from those in dilute solutions in vitro, because the environment in cells is highly concentrated with other macromolecules. This volume exclusion because of macromolecular crowding is predicted to affect both equilibrium and kinetic processes involving protein conformational changes. To quantify macromolecular crowding effects on protein folding mechanisms, we investigated the folding energy landscape of an α/β protein, apoflavodoxin, in the presence of inert macromolecular crowding agents, using in silico and in vitro approaches. By means of coarse-grained molecular simulations and topology-based potential interactions, we probed the effects of increased volume fractions of crowding agents (ϕc) as well as of crowding agent geometry (sphere or spherocylinder) at high ϕc. Parallel kinetic folding experiments with purified Desulfovibro desulfuricans apoflavodoxin in vitro were performed in the presence of Ficoll (sphere) and Dextran (spherocylinder) synthetic crowding agents. In conclusion, we identified the in silico crowding conditions that best enhance protein stability, and discovered that upon manipulation of the crowding conditions, folding routes experiencing topological frustrations can be either enhanced or relieved. Our test-tube experiments confirmed that apoflavodoxin's time-resolved folding path is modulated by crowding agent geometry. Macromolecular crowding effects may be a tool for the manipulation of protein-folding and function in living cells.

Macromolecular crowding modulates folding mechanism of alpha/beta protein apoflavodoxin

Homouz, Dirar; Stagg, Loren; Wittung-Stafshede, Pernilla; Cheung, Margaret S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/10/2008
Relevância na Pesquisa
27.32%
Protein dynamics in cells may be different from that in dilute solutions in vitro since the environment in cells is highly concentrated with other macromolecules. This volume exclusion due to macromolecular crowding is predicted to affect both equilibrium and kinetic processes involving protein conformational changes. To quantify macromolecular crowding effects on protein folding mechanisms, here we have investigated the folding energy landscape of an alpha/beta protein, apoflavodoxin, in the presence of inert macromolecular crowding agents using in silico and in vitro approaches. By coarse-grained molecular simulations and topology-based potential interactions, we probed the effects of increased volume fraction of crowding agents (phi_c) as well as of crowding agent geometry (sphere or spherocylinder) at high phi_c. Parallel kinetic folding experiments with purified Desulfovibro desulfuricans apoflavodoxin in vitro were performed in the presence of Ficoll (sphere) and Dextran (spherocylinder) synthetic crowding agents. In conclusion, we have identified in silico crowding conditions that best enhance protein stability and discovered that upon manipulation of the crowding conditions, folding routes experiencing topological frustrations can be either enhanced or relieved. The test-tube experiments confirmed that apoflavodoxin's time-resolved folding path is modulated by crowding agent geometry. We propose that macromolecular crowding effects may be a tool for manipulation of protein folding and function in living cells.; Comment: to appear in Biophysical Journal (2009). to appear in Biophysical Journal (2009)

Efficient and stable collective choices under crowding preferences

Massó, Jordi; Nicolò, Antonio
Fonte: [S.l.] : Centre de Referencia en Economia Analítica, Publicador: [S.l.] : Centre de Referencia en Economia Analítica,
Tipo: Trabalho em Andamento Formato: application/pdf; application/pdf
Publicado em //2004 ENG
Relevância na Pesquisa
36.84%
We consider a set of agents who have to choose one alternative among a finite set of social alternatives. A final allocation is a pair given by the selected alternative and the group of its users. Agents have crowding preferences over allocations: between any pair of allocations with the same alternative, they prefer the allocation with the largest number of users. We require that a decision be efficient and stable (which guarantees free participation in the group of users and free exit from it). We propose a two-stage sequential mechanism whose unique subgame perfect equilibrium outcome is an efficient and stable allocation which also satisfies a maximal participation property. The social choice function implemented by the proposed mechanism is also anonymous and group stable.