Like all phages, T4 requires a holin (T) to effect lysis. The lysis event depends on the temporally regulated action of T, which accumulates in the inner membrane (IM) until, at an allele-specific time, it triggers to form a large "hole" in the membrane. Hole formation then releases T4 lysozyme into the periplasm where it degrades the cell wall to elicit cell lysis. Unlike other phages, T4 is unique in exhibiting real-time regulation of lysis based on environmental conditions. Specifically, lysis can be delayed indefinitely in the lysis-inhibited state (LIN), where the normal temporal schedule for holin-triggering is over-ridden. Recently, it was shown that the imposition of LIN was correlated with the interaction of the periplasmic domains (PD) of RI and T. These studies have been extended in this dissertation using genetic, biochemical, and structural techniques to address the molecular mechanism of the RI-T LIN system. First, the PD of RI and an RI-T complex were purified, characterized biophysically, and crystallized to yield the first atomic resolution structures of either a holin or antiholin. The RI PD is mostly alpha-helical that undergoes a conformational change, as revealed by NMR spectroscopy studies, when bound to T. The PD of T is globular with alpha-helical, beta strand, and random coil secondary structures. Additionally, the holin was genetically characterized by mutagenesis techniques, yielding new information on its role in both lysis and LIN. Lysis defective mutants in all three topological domains: cytoplasmic, transmembrane, and periplasmic, were isolated. Analysis of these mutants revealed that both the cytoplasmic and periplasmic domains are important in the oligomerization of T. During LIN, the RI PD binds the PD of T, blocking a holin oligomerization interface. Finally, the signal for the imposition of lysis inhibition has been elucidated using NMR spectroscopy and other in vitro studies. These studies have shown that the RI PD binds DNA. From these studies, new models for lysis and LIN have been constructed. Lysis occurs with the accumulation and oligomerization of T via cytoplasmic and periplasmic domain interactions. LIN is imposed when the ectopically localized DNA of a superinfecting phage interacts with RI, stabilizing it in a conformation competent in inhibiting T oligomerization and leading to lysis inhibition.

Objective - The majority of apoptotic cells in atherosclerotic lesions are macrophages. However, the pathogenic role of macrophage apoptosis in the development of atherosclerosis remains unclear. Elevated expression of Bax, one of the pivotal proapoptotic proteins of the Bcl-2 family, has been found in human atherosclerotic plaques. Activation of Bax also occurs in free cholesterol-loaded and oxysterol-treated mouse macrophages. In this study, we examined the effect of Bax deficiency in bone marrow-derived leukocytes on the development of atherosclerosis in low-density lipoprotein receptor-null (LDLR-/-) mice. Methods and Results - Fourteen 8-week-old male LDLR-/- mice were lethally irradiated and reconstituted with either wild-type (WT) C57BL6 or Bax-null (Bax-/-) bone marrow. Three weeks later, the mice were challenged with a Western diet for 10 weeks. No differences were found in the plasma cholesterol level between the WT and Bax-/- group. However, quantitation of cross sections from proximal aorta revealed a 49.2% increase (P=0.0259) in the mean lesion area of the Bax-/- group compared with the WT group. A 53% decrease in apoptotic macrophages in the Bax-/- group was found by TUNEL staining (P<0.05). Conclusions - The reduction of apoptotic activity in macrophages stimulates atherosclerosis in LDLR-/- mice, which is consistent with the hypothesis that macrophage apoptosis suppresses the development of atherosclerosis.

The functional and pathogenic roles of biomolecules are often coupled to the self-association of their basic units into oligomers and aggregates whose structural details are difficult to distinguish because of their insoluble and heterogenous nature. This work focuses on DNA G-quadruplex motifs and amyloid peptides whose oligomers and aggregates are associated with numerous biological roles and human diseases. Infrared (IR) spectroscopy is a powerful tool which probes vibrational transitions whose signatures report on their arrangement within molecules. Advances in two-dimensional infrared (2D IR) spectroscopy have allowed structural characterization in increasingly complex biomolecules that are not amenable to traditional high-resolution techniques. However, careful consideration of the physical phenomena that lead to IR spectra are necessary to make accurate assignments. In the first portion of this work, using FTIR and 2D IR, we determine spectral markers that can differentiate size, metal ion coordination, and topology in DNA G-quadruplex motifs. IR studies aided by isotope labeling define the physical origin of these markers and allow for the construction of a structural landscape in parallel DNA G-quadruplex motifs. It is also shown that 2D IR and isotope editing probes site-specific structural changes in G-quadruplex motifs that can differentiate ion identity and location based on spectral shifts. In the latter portion of this work, we use a combination of spectroscopy and imaging techniques to show that a peptide derived from the human pro-apoptotic protein BAX forms amyloid aggregates whose structure is dependent on the presence of model membranes. Combined, the work in this thesis allows for the formulation of multiple hypotheses based on IR structural assignments regarding disease states and functional mechanisms of these systems.

No description available.

No description available.

Bax is an essential mediator of cell fate. Since its discovery in 1985 as a protein that interacts with the anti-apoptotic protein, Bcl-2, key elements related to its function, structure and regulation remains to be determined. To this end, mitochondrial metabolism was examined in non-apoptotic Bax-deficient HCT-116 cells as well as primary hepatocytes from Bax-deficient mice. Although mitochondrial density and mitochondrial DNA content was the same in Bax-containing and Bax -deficient cells, MitoTracker staining patterns differed, suggesting the existence of Bax -dependent functional differences in mitochondrial physiology. Oxygen consumption and cellular ATP levels were reduced in Bax -deficient cells, while glycolysis was increased. These results suggest that cells lacking Bax have a deficiency in the ability to generate ATP through cellular respiration, supported by detection of reduced citrate synthase activity in Bax -deficient cells. Expression of either full length or C-terminal truncated Bax in Bax -deficient cells rescued ATP synthesis and oxygen consumption and reduced glycolytic activity, suggesting that this metabolic function of Bax was not dependent upon its C-terminal helix. Expression of BCL-2 in Bax-containing cells resulted in a subsequent loss of ATP measured, implying that, even under non-apoptotic conditions, an antagonistic interaction exists between the two proteins. Bax is composed of nine alpha-helices. While three of these helices have features of a trans-membrane region, the contribution of each domain to the apoptotic or non-apoptotic functions of Bax remains unknown. To examine this, we focused on the C-terminal alpha-9 helix, an amphipathic domain with putative membrane binding iv properties and discovered that it has an inherent membrane-binding and cytotoxic capacity. A peptide based on the last twenty amino acids (CT20p) of the alpha-9 helix was synthesized and proved a potent inducer of cell death independent of any apoptotic stimuli. The solubility of CT20p allowed it to be encapsulated in polymeric nanoparticles (NPs), and these CT20p-NPs caused the death of colon and breast cancer cells in vitro and induced tumor regression in vivo, using a murine breast cancer tumor model. CT20p caused increased mitochondrial membrane potential followed by cell death via membrane rupture, without the characteristic membrane asymmetry associated with apoptosis. Hence, while CT20p is based on Bax, its innate cytotoxic activity is unlike the parent protein and could be a powerful anti-cancer agent that bypasses drug resistance, can be encapsulated in tumor-targeted nanoparticles and has potential application in combination therapies to activate multiple death pathways in cancer cells. While previous work revealed novel aspects of the biology of Bax that were unrecognized, new structural information is needed to fully elucidate the complexity of Bax’s function. One approach is to use computational modeling to assess the solved structure of Bax and provide insight into the structural components involved in the activity of the protein. Use of molecular dynamics simulators such as GROMACS, as well as other computational tools provides a powerful means by which to test the feasibility of certain modifications in defined parameters. Such work revealed that the removal of the C-terminal alpha-9 helix of Bax, which normally resides within a hydrophobic pocket, significantly destabilized the protein, perhaps explaining how the protein transitions from soluble to membrane-bound form and maintain energy v production via aerobic respiration or, conversely, how the C-terminus helix conveys cytotoxicity. Collectively, this work reveals that Bax is more than an inducer of cell death but has complex activities yet to be determined.

No description available.

No description available.

Procurando compreender o envolvimento da aldosterona (Aldo) na injúria renal, o objetivo deste projeto foi avaliar o efeito do tratamento crônico com Aldo sobre a função renal e a histologia das arteríolas renais, procurando correlacionar os achados com a expressão de genes reguladores do processo de fibrose e apoptose. A Aldo não alterou os parâmetros fisiológicos, PA, ritmo de filtração glomerular (estimado pela depuração plasmática de creatinina), proteinúria e a morfologia das arteríolas corticais. No entanto, aumentou a expressão do RNAm para TGF-&beta;1, PAI-1 e BAX no tecido renal, além da contagem de células TUNEL positivas nos glomérulos. O antagonismo ao receptor MR (pelo uso da espironolactona) aboliu o efeito hormonal somente sobre a expressão do RNAm para BAX e a marcação do DNA degradado (TUNEL), enquanto que o antagonismo ao GR (pelo uso do RU 486) reduziu ou aboliu todos os efeitos da Aldo. Os resultados indicam que a Aldo pode induzir respostas precoces sobre o remodelamento do tecido renal, sem ainda comprometer a função renal ou alterar a PA. Essas respostas foram independentes da sobrecarga de sal e ocorreram por um mecanismo que envolveu os receptores MR e GR. / In order to understand the aldosterone (Aldo) involvement in renal injury, the objective of this project was to evaluate the effect of Aldo chronic treatment on renal function and renal arterioles histology, trying to correlate the findings with the regulatory genes of fibrosis and apoptosis. Aldo did not change the physiological parameters, BP, glomerular filtration rate (estimated by creatinina clearance), proteinuria and cortical arterioles morphology. However, Aldo increased mRNA expression for TGF-&beta;1, PAI-1 and BAX in renal tissue, as well as TUNEL-positive cell count in glomeruli. MR receptor antagonism (by spironolactone) abolished only the hormonal effect on the mRNA expression for BAX and degraded DNA labeling (TUNEL); whereas GR antagonism (by RU 486) reduced or abolished all Aldo effects. The results indicated that Aldo can induce early responses on renal tissue remodeling, without altering renal function or BP. These responses were salt independent and involved MR and GR receptors.

Made available in DSpace on 2016-08-10T10:38:36Z (GMT). No. of bitstreams: 1 DIEGO FRANCIEL MARQUES MUHLBEIER.pdf: 2283104 bytes, checksum: 4b3910db11a5426da6161c55a1de78bc (MD5) Previous issue date: 2012-03-12 / Sarcomas are a heterogeneous group of tumors that arise from mesenchymal tissues which represent about 1% of all diagnosed solid malignant tumors in adults. Changes that affect the tumor growth such as the deregulation of apoptosis, through overexpression of the Bcl-2 family proteins, have been associated with the prognosis of patients in various types of cancers, including soft tissue sarcomas (SPM). The Bcl-2 family proteins include anti-apoptotic and proapoptotic proteins such as proteins Bcl-2 and Bax, respectively. Despite the evidence, the prognostic value of these proteins, as well as the association with clinicopathological factors, remain controversial. The objective of this study was to investigate the clinical significance of the expression of apoptosis-related markers Bcl-2 and Bax in 86 patients with STS of extremities by immunohistochemical analysis on a tissue microarray construction. Cytoplasmic expression of Bax and Bcl-2 was detected in 25.9% and 66.7% of the cases, respectively. Overexpression of both Bcl-2 and Bax was directly associated with synovial sarcoma, histological grade and clinical stage. A significant association between Bax and Bcl-2 expression was also observed. The 5-year overall survival (OS) for the group was 57%, being lower for cases with Bcl-2 overexpression (47.6% vs 58.3%) and Bax overexpression (50% vs 66.7%), although such difference was not significant. After multivariate analysis, the histological grade remained as an independent prognostic factor (p=0.043, HR=8.0, 95% CI, 1.1-60.1). Bcl-2 family proteins have been tested as therapeutic targets in some clinical studies in several cancers. In our study, overexpression of both Bcl-2 and Bax was associated with histological grade and clinical stage of the tumors, which are classical factors of poor prognosis. Thus, we suggest the use of these proteins as potential prognostic markers in STS of extremities, providing a more appropriate therapeutic planning for each patient. / Os sarcomas constituem um grupo heterogêneo de tumores que surgem a partir de tecidos mesenquimais e que representam cerca de 1% de todos os tumores sólidos malignos diagnosticados em adultos. Alterações que afetam o crescimento tumoral, como a desregulação da apoptose, por meio da hiperexpressão de proteínas da família Bcl-2, têm sido associadas ao prognóstico dos pacientes em diversos tipos de cânceres, incluindo os sarcomas de partes moles (SPM). A família Bcl-2 inclui proteínas pró-apoptóticas e anti-apoptóticas, tais como as proteínas Bax e Bcl-2, respectivamente. Apesar das evidências, o valor prognóstico dessas proteínas, assim como a associação com fatores clínicopatológicos, ainda permanecem controversos. O objetivo desse estudo foi investigar o significado clínico da via da apoptose, por meio da avaliação da expressão imuno-histoquímica de Bcl-2 e Bax, em um grupo de 86 casos de SPM de extremidades, utilizando microarranjos de tecidos (tissue microarray). A expressão citoplasmática de Bcl-2 e Bax foi detectada em 25,9% e 66,7% dos casos, respectivamente. A hiperexpressão de ambos, Bcl-2 e Bax, foi associada aos sarcomas sinoviais, ao grau histológico e ao estadiamento clínico. Uma associação significativa entre a expressão das proteínas Bcl-2 e Bax também foi observada. A sobrevida global em cinco anos foi de 57%, sendo menor para os casos com hiperexpressão de Bcl-2 (47,6% x 58,3%) e Bax (50% x 66,7%), porém, esta diferença não foi estatisticamente significativa. Após análise multivariada, o grau histológico apresentou-se como fator prognóstico independente (p = 0.043, HR = 8.0, IC 95%, 1.1-60.1). Proteínas da família Bcl-2 vêm sendo testadas como alvos terapêuticos em diversos estudos clínicos em vários tipos de cânceres. Em nosso estudo, a expressão de Bcl-2 e Bax foi associada com o grau histológico e o estadiamento clínico, que são fatores clássicos de mau prognóstico. Assim, sugerimos o uso da expressão imunohistoquímica de Bcl-2 e Bax como potencial marcador prognóstico em SPM de extremidades, possibilitando um planejamento terapêutico mais adequado para cada caso.