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Search Results: 1 - 10 of 203168 matches for " Krzysztof P Bielawski "
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Superoxide dismutase is upregulated in Staphylococcus aureus following protoporphyrin-mediated photodynamic inactivation and does not directly influence the response to photodynamic treatment
Joanna Nakonieczna, Ewelina Michta, Magda Rybicka, Mariusz Grinholc, Anna Gwizdek-Wi?niewska, Krzysztof P Bielawski
BMC Microbiology , 2010, DOI: 10.1186/1471-2180-10-323
Abstract: The effectiveness of photodynamic inactivation towards S. aureus and its Sod isogenic mutants deprived of either of the two superoxide dismutase activities, namely SodA or SodM or both of them showed similar results, regardless of the Sod status in TSB medium. On the contrary, in the CL medium (without Mn++ ions) the double SodAM mutant was highly susceptible to photodynamic inactivation. Among 8 clinical isolates of S. aureus analyzed (4 MRSA and 4 MSSA), strains highly resistant and strains highly vulnerable to photodynamic inactivation were noticed. We observed that Sod activity as well as sodA and sodM transcript level increases after protoporphyrin IX-based photodynamic treatment but only in PDI-sensitive strains.We confirmed that porphyrin-based photokilling efficacy is a strain-dependent phenomenon. We showed that oxidative stress sensitivity caused by the lack of both Sod enzymes can be relieved in the presence of Mn ions and partially in the presence of Fe ions. The fact that Sod activity increase is observed only in PDI-susceptible cells emphasizes that this is probably not a direct factor affecting S. aureus vulnerability to porphyrin-based PDI.Staphylococcus aureus, a major human pathogen causes a wide range of disease syndromes, including life-threatening endocarditis, meningitidis and pneumonia. According to the Centers for Disease Control and Prevention this bacterium has been reported to be the most significant cause of serious infections in the United States [1]. S. aureus is able to cause and develop an infection very efficiently due to its ability to produce a few dozen of virulence factors, on one hand, and an ease of antibiotic resistance development, on the other. The most dangerous are methicillin-resistant S. aureus (MRSA) strains, constituting 50% of hospital-aquired isolates as well as emerging vancomycin-resistant variants, isolated from some hospital settings [2].Among several virulence factors, S. aureus produces enzymes responsible for
The role of MR imaging in detection of hepatic iron overload in patients with cirrhosis of different origins
Edyta Szurowska, Katarzyna Sikorska, E I?ycka-?wieszewska, Tomasz Nowicki, Tomasz Romanowski, Krzysztof P Bielawski, Micha? Studniarek
BMC Gastroenterology , 2010, DOI: 10.1186/1471-230x-10-13
Abstract: The purpose of the study was to evaluate usefulness of MR imaging in the detection of hepatic iron overload in patients with cirrhosis of different origins.MR imaging at 1.5T was prospectively performed in 44 patients with liver cirrhosis who had undergone liver biopsy with histopathological assessment of hepatic iron deposits. In all patients the following sequences were used: SE, Express, GRE in T2 and T1-weighted images. Signal intensity (SI) was measured on images obtained with each T2 weighted sequence by means of regions of interest, placed in the liver and paraspinal muscles. The correlation between iron overload, histopathological score, serum ferritin and SI ratio was analyzed.In 20 patients with iron overload confirmed by the biopsy, the liver parenchyma demonstrated lower signal intensity than that of paraspinal muscles. This effect was visible only in 8 patients with hepatic iron overload in Express T2-weighted images. Higher signal intensity of liver than that of skeletal muscles on GRE - T2 weighted images was noted in 24 patients with cirrhosis and without elevated hepatic iron concentration. We observed a correlation between low and high iron concentration and liver to muscle SI ratio.MR imaging is a useful and fast noninvasive diagnostic tool for the detection of liver iron overload in patients with cirrhosis of different origins.Liver to muscle SI ratio in GRE-T2-weighted sequence facilitates to differentiate patients with low and high degree of hepatic iron overload, which correlates with the origin of liver cirrhosis.There are many entities in human pathology with hepatic iron overload. There is controversy regarding nomenclature of these states, however, the classic example of primary iron overload is defined as hereditary hemochromatosis (HH). HH is one of the most common genetic disorders and the second most frequent metabolic liver disease - with the frequency of 3-8 cases/1000 people [1-3]. HFE gene is involved in most cases of hereditary he
Wp yw polimorfizmu wirusa zapalenia w troby typu B na przebieg choroby u osób przewlekle zaka onych
Magda Rybicka,Piotr Stalke,Urszula Charmuszko,Krzysztof Piotr Bielawski
Post?py Higieny i Medycyny Do?wiadczalnej , 2011,
Abstract: Hepatitis B virus (HBV) infection is one of the major human health problems worldwide. It is estimated that chronic HBV infection affects more than 350 million people globally. It is one of the leading causes of liver cirrhosis and hepatocellular carcinoma. High genetic variability is a characteristic feature of HBV as the viral polymerase lacks proofreading activity. The nucleotide substitution rate for HBV is 10-fold higher than for other DNA viruses.Genetic variations of HBV influence the clinical outcome of HBV infection. There are eight genotypes of hepatitis B virus (A–H) that have a distinct geographical distribution. There is clinical significance of HBV genotype in terms of disease activity, risk of progression to cirrhosis, the development of hepatocellular carcinoma and response to antiviral treatments. Moreover, polymorphism in HBV viral polymerase influences the development of HBV mutants resistant to nucleotide analogue treatment that is a consequence of treatment failure.
Positive Darwinian Selection in the Piston That Powers Proton Pumps in Complex I of the Mitochondria of Pacific Salmon
Michael R. Garvin,Joseph P. Bielawski,Anthony J. Gharrett
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0024127
Abstract: The mechanism of oxidative phosphorylation is well understood, but evolution of the proteins involved is not. We combined phylogenetic, genomic, and structural biology analyses to examine the evolution of twelve mitochondrial encoded proteins of closely related, yet phenotypically diverse, Pacific salmon. Two separate analyses identified the same seven positively selected sites in ND5. A strong signal was also detected at three sites of ND2. An energetic coupling analysis revealed several structures in the ND5 protein that may have co-evolved with the selected sites. These data implicate Complex I, specifically the piston arm of ND5 where it connects the proton pumps, as important in the evolution of Pacific salmon. Lastly, the lineage to Chinook experienced rapid evolution at the piston arm.
Improving Evolutionary Models for Mitochondrial Protein Data with Site-Class Specific Amino Acid Exchangeability Matrices
Katherine A. Dunn, Wenyi Jiang, Christopher Field, Joseph P. Bielawski
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0055816
Abstract: Adequate modeling of mitochondrial sequence evolution is an essential component of mitochondrial phylogenomics (comparative mitogenomics). There is wide recognition within the field that lineage-specific aspects of mitochondrial evolution should be accommodated through lineage-specific amino-acid exchangeability matrices (e.g., mtMam for mammalian data). However, such a matrix must be applied to all sites and this implies that all sites are subject to the same, or largely similar, evolutionary constraints. This assumption is unjustified. Indeed, substantial differences are expected to arise from three-dimensional structures that impose different physiochemical environments on individual amino acid residues. The objectives of this paper are (1) to investigate the extent to which amino acid evolution varies among sites of mitochondrial proteins, and (2) to assess the potential benefits of explicitly modeling such variability. To achieve this, we developed a novel method for partitioning sites based on amino acid physiochemical properties. We apply this method to two datasets derived from complete mitochondrial genomes of mammals and fish, and use maximum likelihood to estimate amino acid exchangeabilities for the different groups of sites. Using this approach we identified large groups of sites evolving under unique physiochemical constraints. Estimates of amino acid exchangeabilities differed significantly among such groups. Moreover, we found that joint estimates of amino acid exchangeabilities do not adequately represent the natural variability in evolutionary processes among sites of mitochondrial proteins. Significant improvements in likelihood are obtained when the new matrices are employed. We also find that maximum likelihood estimates of branch lengths can be strongly impacted. We provide sets of matrices suitable for groups of sites subject to similar physiochemical constraints, and discuss how they might be used to analyze real data. We also discuss how the general approach might be employed to improve a variety of mitogenomic-based research activities.
Reducible spectral curves and the hyperkaehler geometry of adjoint orbits
Roger Bielawski
Mathematics , 2006,
Abstract: We study the hyperkaehler geometry of a regular semisimple adjoint orbit of SL(k,C) via the algebraic geometry of the corresponding reducible spectral curve.
Quivers and Poisson structures
Roger Bielawski
Mathematics , 2011,
Abstract: We produce natural quadratic Poisson structures on moduli spaces of representations of quivers. In particular, we study a natural Poisson structure for the generalised Kronecker quiver with 3 arrows.
Nonnegative polynomials from vector bundles on real curves
Roger Bielawski
Mathematics , 2012, DOI: 10.1112/blms/bdt034
Abstract: We observe that the E-resultant of a very ample rank 2 vector bundle E on a real projective curve (with no real points) is nonnegative when restricted to the space of real sections. Moreover, we show that if E has a section vanishing at exactly two points and the degree d of E satisfies d(d-6)> 4g-5, then this polynomial cannot be written as a sum of squares.
Slices to sums of adjoint orbits, the Atiyah-Hitchin manifold, and Hilbert schemes of points
Roger Bielawski
Mathematics , 2015,
Abstract: We show that the regular Slodowy slice to the sum of two semisimple adjoint orbits of $GL(n,C)$ is isomorphic to the deformation of the $D_2$-singularity if $n=2$, the Dancer deformation of the double cover of the Atiyah-Hitchin manifold if $n=3$, and to the Atiyah-Hitchin manifold itself if $n=4$. For higher $n$, such slices to the sum of two orbits, each having only two distinct eigenvalues, are either empty or biholomorphic to open subsets of the Hilbert scheme of points on of one the above surfaces. In particular, these open subsets of Hilbert schemes of points carry complete hyperk\"ahler metrics. In the case of the double cover of the Atiyah-Hitchin manifold this turns out to be the natural $L^2$-metric on a hyperk\"ahler submanifold of the monopole moduli space.
Line bundles on spectral curves and the generalised Legendre transform construction of hyperkaehler metrics
Roger Bielawski
Mathematics , 2008, DOI: 10.1016/j.geomphys.2008.11.010
Abstract: An analogue of the correspondence between GL(k)-conjugacy classes of matricial polynomials and line bundles is given for K-conjugacy classes, where K is one of the following: maximal parabolic, maximal torus, GL(k-1) embedded diagonally. The generalised Legendre transform construction of hyperkaehler metrics is studied further, showing that many known hyperkaehler metrics (including the ones on coadjoint orbits) arise in this way, and giving a large class of new (pseudo-)hyperkaehler metrics, analogous to monopole metrics.
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