14 research outputs found

    Xanthogranulomatous Cholecystitis Masquerading as Gallbladder Cancer: Can It Be Diagnosed Preoperatively?

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    Background. Xanthogranulomatous cholecystitis (XGC) is often misdiagnosed as gallbladder cancer (GBC). We aimed to determine the preoperative characteristics that could potentially aid in an accurate diagnosis of XGC masquerading as GBC. Methods. An analysis of patients operated upon with a preoperative diagnosis of GBC between January 2008 and December 2012 was conducted to determine the clinical and radiological features which could assist in a preoperative diagnosis of XGC. Results. Out of 77 patients who underwent radical cholecystectomy, 16 were reported as XGC on final histopathology (Group A), while 60 were GBC (Group B). The incidences of abdominal pain, cholelithiasis, choledocholithiasis, and acute cholecystitis were significantly higher in Group A, while anorexia and weight loss were higher in Group B. On CT, diffuse gallbladder wall thickening, continuous mucosal line enhancement, and submucosal hypoattenuated nodules were significant findings in Group A. CT findings on retrospect revealed at least one of these findings in 68.7% of the cases. Conclusion. Differentiating XGC from GBC is difficult, and a definitive diagnosis still necessitates a histopathological examination. An accurate preoperative diagnosis requires an integrated review of clinical and characteristic radiological features, the presence of which may help avoid radical resection and avoidable morbidity in selected cases

    General Stability Analysis of Synchronized Dynamics in Coupled Systems

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    We consider the stability of synchronized states (including equilibrium point, periodic orbit or chaotic attractor) in arbitrarily coupled dynamical systems (maps or ordinary differential equations). We develop a general approach, based on the master stability function and Gershgorin disc theory, to yield constraints on the coupling strengths to ensure the stability of synchronized dynamics. Systems with specific coupling schemes are used as examples to illustrate our general method.Comment: 8 pages, 1 figur

    Development of Assay Systems for Amber Codon Decoding at the Steps of Initiation and Elongation in Mycobacteria

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    Genetic analysis of the mechanism of protein synthesis in Gram-positive bacteria has remained largely unexplored because of the unavailability of appropriate in vivo assay systems. We developed chloramphenicol acetyltransferase (CAT)-based in vivo reporter systems to study translation initiation and elongation in Mycobacterium smegmatis. The CAT reporters utilize specific decoding of amber codons by mutant initiator tRNA (i-tRNA, metU) molecules containing a CUA anticodon (metUcuA). The assay systems allow structure-function analyses of tRNAs without interfering with the cellular protein synthesis and function with or without the expression of heterologous GInRS from Escherichia coll. We show that despite their naturally occurring slow-growth phenotypes, the step of i-tRNA formylation is vital in translation initiation in mycobacteria and that formylation-deficient i-tRNA mutants (MetU(CUA/A1), MetU(CUA/G72), and metU(CUA/G72G73)) with a Watson-Crick base pair at the 1.72 position participate in elongation. In the absence of heterologous GInRS expression, the mutant tRNAs are predominantly aminoacylated (glutamylated) by nondiscriminating GIuRS. Acid urea gels show complete transamidation of the glutamylated metU(CUA/G72G73) tRNA to its glutaminylated form (by GatCAB) in M. smegmatis. In contrast, the glutamylated metU(CUA/G72) tRNA did not show a detectable level of transamidation. Interestingly, the metU(CUA/A1) mutant showed an intermediate activity of transamidation and accumulated in both glutamylated and glutaminylated forms. These observations suggest important roles for the discriminator base position and/or a weak Watson-Crick base pair at 1.72 for in vivo recognition of the glutamylated tRNAs by M. smegmatis GatCAB. IMPORTANCE Genetic analysis of the translational apparatus in Gram-positive bacteria has remained largely unexplored because of the unavailability of appropriate in vivo assay systems. We developed chloramphenicol acetyltransferase (CAT)-based reporters which utilize specific decoding of amber codons by mutant tRNAs at the steps of initiation and/or elongation to allow structure-function analysis of the translational machinery. We show that formylation of the initiator tRNA (i-tRNA) is crucial even for slow-growing bacteria and that i-tRNA mutants with a CUA anticodon are aminoacylated by nondiscriminating GIuRS. The discriminator base position, and/or a weak Watson-Crick base pair at the top of the acceptor stem, provides important determinants for transamidation of the i-tRNA-attached Glu to Gln by the mycobacterial GatCAB

    Development of Assay Systems for Amber Codon Decoding at the Steps of Initiation and Elongation in Mycobacteria

    No full text
    Genetic analysis of the mechanism of protein synthesis in Gram-positive bacteria has remained largely unexplored because of the unavailability of appropriate in vivo assay systems. We developed chloramphenicol acetyltransferase (CAT)-based in vivo reporter systems to study translation initiation and elongation in Mycobacterium smegmatis. The CAT reporters utilize specific decoding of amber codons by mutant initiator tRNA (i-tRNA, metU) molecules containing a CUA anticodon (metUcuA). The assay systems allow structure-function analyses of tRNAs without interfering with the cellular protein synthesis and function with or without the expression of heterologous GInRS from Escherichia coll. We show that despite their naturally occurring slow-growth phenotypes, the step of i-tRNA formylation is vital in translation initiation in mycobacteria and that formylation-deficient i-tRNA mutants (MetU(CUA/A1), MetU(CUA/G72), and metU(CUA/G72G73)) with a Watson-Crick base pair at the 1.72 position participate in elongation. In the absence of heterologous GInRS expression, the mutant tRNAs are predominantly aminoacylated (glutamylated) by nondiscriminating GIuRS. Acid urea gels show complete transamidation of the glutamylated metU(CUA/G72G73) tRNA to its glutaminylated form (by GatCAB) in M. smegmatis. In contrast, the glutamylated metU(CUA/G72) tRNA did not show a detectable level of transamidation. Interestingly, the metU(CUA/A1) mutant showed an intermediate activity of transamidation and accumulated in both glutamylated and glutaminylated forms. These observations suggest important roles for the discriminator base position and/or a weak Watson-Crick base pair at 1.72 for in vivo recognition of the glutamylated tRNAs by M. smegmatis GatCAB. IMPORTANCE Genetic analysis of the translational apparatus in Gram-positive bacteria has remained largely unexplored because of the unavailability of appropriate in vivo assay systems. We developed chloramphenicol acetyltransferase (CAT)-based reporters which utilize specific decoding of amber codons by mutant tRNAs at the steps of initiation and/or elongation to allow structure-function analysis of the translational machinery. We show that formylation of the initiator tRNA (i-tRNA) is crucial even for slow-growing bacteria and that i-tRNA mutants with a CUA anticodon are aminoacylated by nondiscriminating GIuRS. The discriminator base position, and/or a weak Watson-Crick base pair at the top of the acceptor stem, provides important determinants for transamidation of the i-tRNA-attached Glu to Gln by the mycobacterial GatCAB

    Mycobacterium tuberculosis mutT1 (Rv2985) and ADPRase (Rv1700) proteins constitute a two-stage mechanism of 8-Oxo-dGTP and 8-Oxo-GTP detoxification and adenosine to cytidine mutation avoidance

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    Approximately one third of the world population is infected with Mycobacterium tuberculosis, the causative agent of tuberculosis. A better understanding of the pathogen biology is crucial to develop new tools/strategies to tackle its spread and treatment. In the host macrophages, the pathogen is exposed to reactive oxygen species, known to damage dGTP and GTP to 8-oxo-dGTP and 8-oxo-GTP, respectively. Incorporation of the damaged nucleotides in nucleic acids is detrimental to organisms. MutT proteins, belonging to a class of Nudix hydrolases, hydrolyze 8-oxo-G nucleoside triphosphates/diphosphates to the corresponding nucleoside monophosphates and sanitize the nucleotide pool. Mycobacteria possess several MutT proteins. However, a functional homolog of Escherichia coli MutT has not been identified. Here, we characterized MtuMutT1 and Rv1700 proteins of M. tuberculosis. Unlike other MutT proteins, MtuMutT1 converts 8-oxo-dGTP to 8-oxo-dGDP, and 8-oxo-GTP to 8-oxo-GDP. Rv1700 then converts them to the corresponding nucleoside monophosphates. This observation suggests the presence of a two-stage mechanism of 8-oxo-dGTP/8-oxo-GTP detoxification in mycobacteria. MtuMutT1 converts 8-oxo-dGTP to 8-oxo-dGDP with a K-m of similar to 50 mu M and V-max of similar to 0.9 pmol/min per ng of protein, and Rv1700 converts 8-oxo-dGDP to 8-oxo-dGMP with a K-m of similar to 9.5 mu M and V-max of similar to 0.04 pmol/min per ng of protein. Together, MtuMutT1 and Rv1700 offer maximal rescue to E. coli for its MutT deficiency by decreasing A to C mutations (a hallmark of MutT deficiency). We suggest that the concerted action of MtuMutT1 and Rv1700 plays a crucial role in survival of bacteria against oxidative stress

    Distinctive contributions of the ribosomal P-site elements m(2)G966, m(5)C967 and the C-terminal tail of the S9 protein in the fidelity of initiation of translation in Escherichia coli

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    The accuracy of pairing of the anticodon of the initiator tRNA (tRNA(fMet)) and the initiation codon of an mRNA, in the ribosomal P-site, is crucial for determining the translational reading frame. However, a direct role of any ribosomal element(s) in scrutinizing this pairing is unknown. The P-site elements, m(2)G966 (methylated by RsmD), m(5)C967 (methylated by RsmB) and the C-terminal tail of the protein S9 lie in the vicinity of tRNA(fMet). We investigated the role of these elements in initiation from various codons, namely, AUG, GUG, UUG, CUG, AUA, AUU, AUC and ACG with tRNA(CAU)(fmet) (tRNA(fMet) with CAU anticodon); CAC and CAU with tRNA(GUG)(fme); UAG with tRNA(GAU)(fMet) using in vivo and computational methods. Although RsmB deficiency did not impact initiation from most codons, RsmD deficiency increased initiation from AUA, CAC and CAU (2- to 3.6-fold). Deletion of the S9 C-terminal tail resulted in poorer initiation from UUG, GUG and CUG, but in increased initiation from CAC, CAU and UAC codons (up to 4-fold). Also, the S9 tail suppressed initiation with tRNA(CAU)(fMet)lacking the 3GC base pairs in the anticodon stem. These observations suggest distinctive roles of 966/967 methylations and the S9 tail in initiation
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