Broken Promises

I only very recently have become confident in myself. It took me a while to fi nd my footing, to discover who I was and what I am capable of. To get to where I am now, full of potential and excitement for the future, I had to go through a lot of dark spots. I think my story is one that should be told. I am not writing to brag about myself or make me out to be this heroic, strong figure—I’m writing because I want students that find themselves in similar situations to know that they are not alone

Folding and gating of the outer membrane porin PhoE of Escherichia coli

The cell envelope of Gram-negative bacteria, such as Escherichia coli, consists of a double membrane separated by the periplasm. Due to this architecture, the cell can maintain a microenvironment essential for cell viability. Several outer membrane proteins (OMPs), such as PhoE, are implicated in providing the cell of its nutrients. PhoE functions in the outer membrane as a trimeric pore allowing passive diffusion of preferentially anionic compounds with molecular masses up to 600 Da. OMPs are synthesized in the cytoplasm as precursor proteins with an N-terminal extension, the signal sequence. These precursors are translocated across the inner membrane via the Sec machinery, and the signal sequence is cleaved off. In this thesis we addressed the question whether periplasmic intermediates exists in the biogenesis of OMPs. PhoE is used in our laboratory as a model protein to study the biogenesis of OMPs. Artificial disulfide bonds were constructed within and between PhoE monomers, based upon the known 3D-structure. Formation of these disulfide bonds required the presence of the periplamic DsbA and DsbG proteins, respectively, which catalyze disulfide bonds in unfolded and folded structures, respectively. These findings indicated that folding of the monomer and trimer occurs at least partially in the periplsm. Subsequently, it was demonstrated that the periplamic peptidyl-prolyl cis/trans isomerase SurA functions as a chaperone in the biogenesis of PhoE since folding of a PhoE mutant lacking its proline residues still required the presence of SurA. PhoE monomers are foled as a b-barrel with 16-antiparallel b-strands. These strands are connected by short turns at the periplasmic side and long loop at the surface-exposed side of the membrane. The third loop (L3) is folded into the barrel, thereby forming a constriction at half the height of the membrane. The sequence PEFGG at the tip of L3 is highly conserved in a superfamily of bacterial porins. The L3 is involved in voltage-dependent closing of the pore. In this thesis the channel characteristics of mutant PhoE porins in which either the tip of the constriction loop was connected to the barrel wall or residues within the conserved PEFGG sequence were replaced, were determined. The experiments demonstrated that pore closings are not mediated by a gross movement of L3 within the channel, but by more subtle rearrangements, involving only parts of L3 or the side chains of the charged residues wihtin the constriction zone

Molecular environments of the supernova remnant G359.1−0.5

We report new CO observations and a detailed molecular-line study of the mixed morphology supernova remnant G359.1-0.5, which contains six OH (1720 MHz) masers along the radio shell, indicative of shock-cloud interaction. Observations of 12CO and 13CO J:1-0 lines were performed in a ∼38 × 38 arcmin area with the on-the-fly technique using the Kit Peak 12 Meter telescope. The molecular study has revealed the existence of a few clumps with densities ∼103 cm-3 compatible in velocity and position with the OH (1720 MHz) masers. These clumps, in turn, appear to be part of a larger, elongated molecular structure ∼34 arcmin long extending between -12.48 and +1.83 km s-1, adjacent to the western edge of the radio shell. According to the densities and relative position with respect to the masers, we conclude that the CO clouds depict unshocked gas, as observed in other remnants with OH (1720 MHz) masers. In addition, we investigated the distribution of the molecular gas towards the adjacent γ-ray source HESS J1745-303 (Aharonian et al. 2006) but could not find any morphological correlation between the γ-rays and the CO emission at any velocity in this region.Fil: Eppens, Laura Karina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Reynoso, Estela Marta. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Lazendic Galloway, J. Monash University; AustraliaFil: Combi, Jorge Ariel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Albacete Colombo, Juan Facundo. Universidad Nacional del Comahue; Argentin

Interacción entre el RSN G359.1-0.5 y el medio interestelar

G359.1-0.5 es un remanente de supernova detectado en dirección al centro de la Galaxia que presenta una morfología del tipo cáscara en el continuo de radio y emisión de rayos X extendida de naturaleza térmica en su interior, por lo cual se lo clasifica como perteneciente al tipo de morfología mixta. Los valores de la densidad columnar de H obtenidos sugieren que este remanente está ubicado a una distancia muy cercana al centro de la Galaxia. Los primeros estudios moleculares alrededor de G359.1-0.5 muestran que existe una estructura anular de CO en el rango de velocidades entre −190 y −60 km s−1 , coincidente con una nube de Hi a velocidades similares, concéntrica con el remanente. Sobre el borde de la cáscara de continuo de radio se detectaron seis máseres de OH a 1720 MHz a velocidades cercanas a −5 km s−1 , muy distintas de las encontradas en estudios moleculares anteriores. En este trabajo se identificó una estructura molecular en las líneas de 12CO y 13CO J=1-0 a velocidades entre −12.48 y +1.83 km s−1 con grumos en su interior que aparentemente se encuentran asociados a los máseres de OH. Además, el análisis de los datos de archivo del observatorio XMM-Newton arrojó evidencias de que el gas situado en el interior de G359.1-0.5 no se encontraría en equilibrio de ionización. Finalmente, con los resultados obtenidos se introduce un posible escenario astrofísico para el remanente de supernova G359.1-0.5.G359.1-0.5 is a supernova remnant near the Galactic center region that belongs to the mixed morphology type, showing a radio continuum shell and diffuse thermal X-ray emission inside. Earlier molecular studies around the location of G359.1-0.5 revealed an annular CO structure in the velocity range from −190 to −60 km s−1 with an Hi counterpart, both concentric with the remnant. Six OH masers at 1720 MHz along the edge of the radio-continuum shell were detected at velocities around −5 km s−1 , largely different from those found in previous molecular studies. In this work, we identify a molecular structure in the 12CO and 13CO J=1-0 lines between the velocities −12.48 and +1.83 km s−1 which contains CO clumps apparently related to the OH masers. In addition, analyzing XMM-Newton archival data, we found evidence that part of the interior gas is not in ionization equilibrium. Finally, based on the collected data, we suggest a likely astrophysical scenario for G359.5-0.1.Fil: Eppens, Laura Karina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Reynoso, Estela Marta. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); ArgentinaFil: Combi, Jorge Ariel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; ArgentinaFil: Lazendic Galloway, J.. Monash University; AustraliaReunión Anual de la de la Asociación Argentina de AstronomíaViedmaArgentinaUniversidad de Rio NegroInstituto Argentino de Radioastronomí

Retinal Arteriolar Dilation Predicts Retinopathy in Adolescents With Type 1 Diabetes

OBJECTIVE—Alterations in retinal vascular caliber may reflect early subclinical microvascular dysfunction. In this study, we examined the association of retinal vascular caliber to incident retinopathy in young patients with type 1 diabetes

Factors Affecting the Folding of Pseudomonas aeruginosa OprF Porin into the One-Domain Open Conformer

Pseudomonas aeruginosa OprF is a largely monomeric outer membrane protein that allows the slow, nonspecific transmembrane diffusion of solutes. This protein folds into two different conformers, with the majority conformer folding into a two-domain conformation that has no porin activity and the minority conformer into a one-domain conformation with high porin activity and presumably consisting of a large β barrel. We examined the factors that control the divergent folding pathways of OprF. OprF contains four Cys residues in the linker region connecting the N-terminal β-barrel domain and the C-terminal globular domain in the majority conformer. Prevention of disulfide bond formation either by expression of OprF in an Escherichia coli dsbA strain grown with dithiothreitol or by replacement of all Cys residues with serine (CS OprF) increased the specific pore-forming activity of OprF significantly. Replacement of Phe160 with Ile at the end of the β-barrel termination signal as well as replacement of Lys164 in the linker region with Gly, Cys, or Glu increased porin activity 2-fold. Improving a potential β-barrel termination signal in the periplasmic domain by replacement of Asp211 with asparagine also increased porin activity. The porin activity could be improved about 5-fold by the combination of these replacements. OprF mutants with higher porin activity were shown to contain more one-domain conformers by surface labeling of the A312C residue in intact cells, as this residue is located in the periplasmic domain in the two-domain conformers. Finally, when the OprF protein was expressed in an E. coli strain lacking the periplasmic chaperone Skp, the CS OprF protein exhibited increased pore-forming activity

Timing Is Everything: Age of Onset Influences Long-Term Retinopathy Risk in Type 2 Diabetes, Independent of Traditional Risk Factors

OBJECTIVE—To test the hypothesis that age of type 2 diabetes onset influences inherent susceptibility to diabetic retinopathy, independent of disease duration and degree of hyperglycemia