4 resultados para Reversion to virulence
em Duke University
Resumo:
From April 26-29, 1994, South Africa held its first universal, democratic elections. Witnessed by the world, South Africans of all races waited patiently in line to cast their ballots, signaling the official and symbolic birth of the “new” South Africa. The subsequent years, marked initially with euphoric hopes for racial healing enabled by institutional processes such as the Truth and Reconciliation Commission (TRC), have instead, most recently, inspired deep concern about epidemic levels of HIV/AIDS, violent crime, state corruption, and unbridled market reforms directed at everything from property to bodies to babies. Now, seemingly beleaguered state officials deploy the mantra “TINA” (There Is No Alternative [to neoliberal development]) to fend off criticism of growing income and wealth disparities. To coincide, more or less, with the anniversary of 1994—less to commemorate than to signal something about the trajectory of the past twenty years—we are proposing an interdisciplinary, special theme section of Comparative Studies in South Asia, Africa, and the Middle East (CSSAAME) entitled “The Haunted Present: Reckoning After Apartheid” (tentative title). The special theme section is framed around questions of reckoning in the double sense of both a moral and practical accounting for historical injury alongside the challenges and failures of the no-longer “new” South Africa. Against accounts depicting the liberation era as non-violent and peaceable, more nuanced analysis we argue suggests not only that South Africa’s “revolution” was marked by both collective and individual violence—on the part of the state and the liberation movements—but that reckoning with the present demands of scholars, the media, and cultural commentators that they begin to grapple more fully with the dimensions and different figurations of South Africa’s violent colonial history. Indeed, violence and reckoning appear as two central forces in contemporary South African political, economic, and social life. In response, we are driven to pose the following questions: In the post-apartheid period, what forms of (individual, structural) violence have come to bear on South African life? How does this violence reckon with apartheid and its legacies? Does it in fact reckon with the past? How can we or should we think about violence as a response to the (failed?) reckoning of state initiatives like the TRC? What has enabled or enables aesthetic forms—literature, photography, plastic arts, and other modes of expressive culture—to respond to the difficulties of South Africa’s ongoing transition? What, in fact, would a practice or ethic of reckoning defined in the following way look like? ˈrekəniNG/ noun: • the action or process of calculating or estimating something: last year was not, by any reckoning, a particularly good one; the system of time reckoning in Babylon • a person’s view, opinion, or judgment: by ancient reckoning, bacteria are plants • archaic, a bill or account, or its settlement • the avenging or punishing of past mistakes or misdeeds: the fear of being brought to reckoning there will be a terrible reckoning (Oxford English Dictionary) Looking back on the period, just before 1994, is sobering indeed. At the time, many saw in the energies and courage of those fighting for liberation the possibilities of a post-racial, post-conflict society. Yet as much as the new was ushered in, old apartheid forms lingered. Recalling Nadine Gordimer’s invocation of Gramsci’s “morbid symptoms” more and more it seems “the old is dying and the new cannot be born” (Gramsci cited in Gordimer 1982). And even as the new began to emerge other forces—both internal and external to South Africa—redefined the conditions for transformation. The so-called “new” South Africa, as Jennifer Wenzel has argued, was really more than anything “the changing face of old oppressions” (Wenzel 2009:159). The implications for our special theme section of CSSAAME are many. We begin by exploring the gender, race, and class dimensions of contemporary South African life by way of its literatures, histories, and politics, its reversion to custom, the claims of ancestors on the living, in brief, the various cultural expressive modes in which contemporary South Africa reckons with its past and in so doing accounts, day by day, for the ways in which the present can be lived, pragmatically. This moves us some distance from the exercise in “truth and reconciliation” of the earlier post-transition years to consider more fully the nature of post-conflict, the suturing of old enmities in the present, and the ways of resolving those lingering suspicions both ordinary and the stuff of the dark night of the soul (Nelson 2009:xv).
Resumo:
From April 26-29, 1994, South Africa held its first universal, democratic elections. Witnessed by the world, South Africans of all races waited patiently in line to cast their ballots, signaling the official and symbolic birth of the “new” South Africa. The subsequent years, marked initially with euphoric hopes for racial healing enabled by institutional processes such as the Truth and Reconciliation Commission (TRC), have instead, most recently, inspired deep concern about epidemic levels of HIV/AIDS, violent crime, state corruption, and unbridled market reforms directed at everything from property to bodies to babies. Now, seemingly beleaguered state officials deploy the mantra “TINA” (There Is No Alternative [to neoliberal development]) to fend off criticism of growing income and wealth disparities. To coincide, more or less, with the anniversary of 1994—less to commemorate than to signal something about the trajectory of the past twenty years—we are proposing an interdisciplinary, special theme section of Comparative Studies in South Asia, Africa, and the Middle East (CSSAAME) entitled “The Haunted Present: Reckoning After Apartheid” (tentative title). The special theme section is framed around questions of reckoning in the double sense of both a moral and practical accounting for historical injury alongside the challenges and failures of the no-longer “new” South Africa. Against accounts depicting the liberation era as non-violent and peaceable, more nuanced analysis we argue suggests not only that South Africa’s “revolution” was marked by both collective and individual violence—on the part of the state and the liberation movements—but that reckoning with the present demands of scholars, the media, and cultural commentators that they begin to grapple more fully with the dimensions and different figurations of South Africa’s violent colonial history. Indeed, violence and reckoning appear as two central forces in contemporary South African political, economic, and social life. In response, we are driven to pose the following questions: In the post-apartheid period, what forms of (individual, structural) violence have come to bear on South African life? How does this violence reckon with apartheid and its legacies? Does it in fact reckon with the past? How can we or should we think about violence as a response to the (failed?) reckoning of state initiatives like the TRC? What has enabled or enables aesthetic forms—literature, photography, plastic arts, and other modes of expressive culture—to respond to the difficulties of South Africa’s ongoing transition? What, in fact, would a practice or ethic of reckoning defined in the following way look like? ˈrekəniNG/ noun: • the action or process of calculating or estimating something: last year was not, by any reckoning, a particularly good one; the system of time reckoning in Babylon • a person’s view, opinion, or judgment: by ancient reckoning, bacteria are plants • archaic, a bill or account, or its settlement • the avenging or punishing of past mistakes or misdeeds: the fear of being brought to reckoning there will be a terrible reckoning (Oxford English Dictionary) Looking back on the period, just before 1994, is sobering indeed. At the time, many saw in the energies and courage of those fighting for liberation the possibilities of a post-racial, post-conflict society. Yet as much as the new was ushered in, old apartheid forms lingered. Recalling Nadine Gordimer’s invocation of Gramsci’s “morbid symptoms” more and more it seems “the old is dying and the new cannot be born” (Gramsci cited in Gordimer 1982). And even as the new began to emerge other forces—both internal and external to South Africa—redefined the conditions for transformation. The so-called “new” South Africa, as Jennifer Wenzel has argued, was really more than anything “the changing face of old oppressions” (Wenzel 2009:159). The implications for our special theme section of CSSAAME are many. We begin by exploring the gender, race, and class dimensions of contemporary South African life by way of its literatures, histories, and politics, its reversion to custom, the claims of ancestors on the living, in brief, the various cultural expressive modes in which contemporary South Africa reckons with its past and in so doing accounts, day by day, for the ways in which the present can be lived, pragmatically. This moves us some distance from the exercise in “truth and reconciliation” of the earlier post-transition years to consider more fully the nature of post-conflict, the suturing of old enmities in the present, and the ways of resolving those lingering suspicions both ordinary and the stuff of the dark night of the soul (Nelson 2009:xv).
Resumo:
Abstract
Listeria monocytogenes is a gram-positive soil saprophytic bacterium that is capable of causing fatal infection in humans. The main virulence regulator PrfA, a member of the Crp/FNR family of transcriptional regulators, activates the expression of essential proteins required for host cell invasion and cell-to-cell spread. The mechanism of PrfA activation and the identity of its small molecule coactivator have remained a mystery for more than 20 years, but it is hypothesized that PrfA shares mechanistic similarity to the E. coli cAMP binding protein, Crp. Crp activates gene expression by binding cAMP, increasing the DNA binding affinity of the protein and causing a significant DNA bend that facilitates RNA polymerase binding and downstream gene activation. Our data suggests PrfA activates virulence protein expression through a mechanism distinct from the canonical Crp activation mechanism that involves a combination of cysteine residue reduction and glutathione (GSH) binding.
Listeria lacking glutathione synthase (ΔgshF) is avirulent in mice; however virulence is rescued when the bacterium expresses the constitutively active PrfA mutant G145S. Interestingly, Listeria expressing a PrfA mutant in which its four cysteines are mutated to alanine (Quad PrfA), demonstrate a 30-fold decrease in virulence. The Quad and ΔgshF double mutant strains are avirulent. DNA-binding affinity, measured through fluorescence polarization assays, indicate reduction of the cysteine side chains is sufficient to allow PrfA to binds its physiological promoters Phly and PactA with low nanomolar affinity. Oxidized PrfA binds the promoters poorly.
Unexpectedly, Quad also binds promoter DNA with nanomolar affinity, suggesting that the cysteines play a role in transcription efficiency in addition to DNA binding. Both PrfA and Quad bind GSH at physiologically relevant and comparable affinities, however GSH did not affect DNA binding in either case. Thermal denaturation assays suggest that Quad and wild-type PrfA differ structurally upon binding GSH, which supports the in vivo difference in infection between the regulator and its mutant.
Structures of PrfA in complex with cognate DNA, determined through X-ray crystallography, further support the disparity between PrfA and Crp activation mechanisms as two structures of reduced PrfA bound to Phly (PrfA-Phly30 and PrfA-Phly24) suggest the DNA adopts a less bent DNA conformation when compared to Crp-cAMP- DNA. The structure of Quad-Phly30 confirms the DNA-binding data as the protein-DNA complex adopts the same overall conformation as PrfA-Phly.
From these results, we hypothesize a two-step activation mechanism wherein PrfA, oxidized upon cell entry and unable to bind DNA, is reduced upon its intracellular release and binds DNA, causing a slight bend in the promoter and small increase in transcription of PrfA-regulated genes. The structures of PrfA-Phly30 and PrfA-Phly24 likely visualize this intermediate complex. Increasing concentrations of GSH shift the protein to a (PrfA-GSH)-DNA complex which is fully active transcriptionally and is hypothesized to resemble closely the transcriptionally active structure of the cAMP-(Crp)-DNA complex. Thermal denaturation results suggest Quad PrfA is deficient in this second step, which explains the decrease in virulence and implicates the cysteine residues as critical for transcription efficiency. Further structural and biochemical studies are on-going to clarify this mechanism of activation.
Resumo:
Dengue is an important vector-borne virus that infects on the order of 400 million individuals per year. Infection with one of the virus's four serotypes (denoted DENV-1 to 4) may be silent, result in symptomatic dengue 'breakbone' fever, or develop into the more severe dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). Extensive research has therefore focused on identifying factors that influence dengue infection outcomes. It has been well-documented through epidemiological studies that DHF is most likely to result from a secondary heterologous infection, and that individuals experiencing a DENV-2 or DENV-3 infection typically are more likely to present with more severe dengue disease than those individuals experiencing a DENV-1 or DENV-4 infection. However, a mechanistic understanding of how these risk factors affect disease outcomes, and further, how the virus's ability to evolve these mechanisms will affect disease severity patterns over time, is lacking. In the second chapter of my dissertation, I formulate mechanistic mathematical models of primary and secondary dengue infections that describe how the dengue virus interacts with the immune response and the results of this interaction on the risk of developing severe dengue disease. I show that only the innate immune response is needed to reproduce characteristic features of a primary infection whereas the adaptive immune response is needed to reproduce characteristic features of a secondary dengue infection. I then add to these models a quantitative measure of disease severity that assumes immunopathology, and analyze the effectiveness of virological indicators of disease severity. In the third chapter of my dissertation, I then statistically fit these mathematical models to viral load data of dengue patients to understand the mechanisms that drive variation in viral load. I specifically consider the roles that immune status, clinical disease manifestation, and serotype may play in explaining viral load variation observed across the patients. With this analysis, I show that there is statistical support for the theory of antibody dependent enhancement in the development of severe disease in secondary dengue infections and that there is statistical support for serotype-specific differences in viral infectivity rates, with infectivity rates of DENV-2 and DENV-3 exceeding those of DENV-1. In the fourth chapter of my dissertation, I integrate these within-host models with a vector-borne epidemiological model to understand the potential for virulence evolution in dengue. Critically, I show that dengue is expected to evolve towards intermediate virulence, and that the optimal virulence of the virus depends strongly on the number of serotypes that co-circulate. Together, these dissertation chapters show that dengue viral load dynamics provide insight into the within-host mechanisms driving differences in dengue disease patterns and that these mechanisms have important implications for dengue virulence evolution.