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191.
Fluorescence-based molecular sensing and cellular imaging are commonly carried out with the application of organic dyes. Quantum dots (QDs) are now recognized as better tools because they are brighter, size tunable, and more photostable than dyes. Most of the proposed QD-based biosensing systems involve elements of known toxicity. The present work reports the functionalization of biocompatible InGaP/ZnS core-shell QDs with anti-bovine serum albumin (anti-BSA) to exploit them as fluorescent probes for antigen detection. Successful bioconjugation was characterized with the absorption and emission spectra showing blue shifts of around 40 and 30 nm, respectively. Gel electrophoresis and particle size distribution studies further confirmed the mass increment of QDs after their functionalization with anti-BSA. Surface plasmon resonance spectrometry has been used to study the affinity of QD-(anti-BSA) probes for bovine serum albumin (BSA). Photoluminescence quenching of the developed probe is observed in the presence of BSA. 相似文献
192.
The ReaxFF interatomic potential, used for organic materials, involves more than 600 adjustable parameters, the best-fit values
of which must be determined for different materials. A new method of determining the set of best-fit parameters for specific
molecules containing carbon, hydrogen, nitrogen and oxygen is presented, based on a parameter reduction technique followed
by genetic algorithm (GA) minimization. This work has two novel features. The first is the use of a parameter reduction technique
to determine which subset of parameters plays a significant role for the species of interest; this is necessary to reduce
the optimization space to manageable levels. The second is the application of the GA technique to a complex potential (ReaxFF)
with a very large number of adjustable parameters, which implies a large parameter space for optimization. In this work, GA
has been used to optimize the parameter set to determine best-fit parameters that can reproduce molecular properties to within
a given accuracy. As a test problem, the use of the algorithm has been demonstrated for nitromethane and its decomposition
products. 相似文献
193.
Pravin Kumar Ankush Jagtap Vijay Soni Neha Vithani Gagan Deep Jhingan Vaibhav Singh Bais Vinay Kumar Nandicoori Balaji Prakash 《The Journal of biological chemistry》2012,287(47):39524-39537
N-Acetyl-glucosamine-1-phosphate uridyltransferase (GlmU), a bifunctional enzyme involved in bacterial cell wall synthesis is exclusive to prokaryotes. GlmU, now recognized as a promising target to develop new antibacterial drugs, catalyzes two key reactions: acetyl transfer and uridyl transfer at two independent domains. Hitherto, we identified GlmU from Mycobacterium tuberculosis (GlmUMtb) to be unique in possessing a 30-residue extension at the C terminus. Here, we present the crystal structures of GlmUMtb in complex with substrates/products bound at the acetyltransferase active site. Analysis of these and mutational data, allow us to infer a catalytic mechanism operative in GlmUMtb. In this SN2 reaction, His-374 and Asn-397 act as catalytic residues by enhancing the nucleophilicity of the attacking amino group of glucosamine 1-phosphate. Ser-416 and Trp-460 provide important interactions for substrate binding. A short helix at the C-terminal extension uniquely found in mycobacterial GlmU provides the highly conserved Trp-460 for substrate binding. Importantly, the structures reveal an uncommon mode of acetyl-CoA binding in GlmUMtb; we term this the U conformation, which is distinct from the L conformation seen in the available non-mycobacterial GlmU structures. Residues, likely determining U/L conformation, were identified, and their importance was evaluated. In addition, we identified that the primary site for PknB-mediated phosphorylation is Thr-418, near the acetyltransferase active site. Down-regulation of acetyltransferase activity upon Thr-418 phosphorylation is rationalized by the structures presented here. Overall, this work provides an insight into substrate recognition, catalytic mechanism for acetyl transfer, and features unique to GlmUMtb, which may be exploited for the development of inhibitors specific to GlmU. 相似文献
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Distinct mechanisms of clathrin-independent endocytosis have unique sphingolipid requirements
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Cheng ZJ Singh RD Sharma DK Holicky EL Hanada K Marks DL Pagano RE 《Molecular biology of the cell》2006,17(7):3197-3210
Sphingolipids (SLs) play important roles in membrane structure and cell function. Here, we examine the SL requirements of various endocytic mechanisms using a mutant cell line and pharmacological inhibitors to disrupt SL biosynthesis. First, we demonstrated that in Chinese hamster ovary cells we could distinguish three distinct mechanisms of clathrin-independent endocytosis (caveolar, RhoA, and Cdc42 dependent) which differed in cargo, sensitivity to pharmacological agents, and dominant negative proteins. General depletion of SLs inhibited endocytosis by each clathrin-independent mechanism, whereas clathrin-dependent uptake was unaffected. Depletion of glycosphingolipids (GSLs; a subgroup of SLs) selectively blocked caveolar endocytosis and decreased caveolin-1 and caveolae at the plasma membrane. Caveolar endocytosis and PM caveolae could be restored in GSL-depleted cells by acute addition of exogenous GSLs. Disruption of RhoA- and Cdc42-regulated endocytosis by SL depletion was shown to be related to decreased targeting of these Rho proteins to the plasma membrane and could be partially restored by exogenous sphingomyelin but not GSLs. Both the in vivo membrane targeting and in vitro binding to artificial lipid vesicles of RhoA and Cdc42 were shown to be dependent upon sphingomyelin. These results provide the first evidence that SLs are differentially required for distinct mechanisms of clathrin-independent endocytosis. 相似文献
197.
Kamal A Kumar BA Suresh P Agrawal SK Chashoo G Singh SK Saxena AK 《Bioorganic & medicinal chemistry》2010,18(24):8493-8500
A new class of 4β-N-polyaromatic substituted podophyllotoxin congeners have been synthesized and evaluated for their DNA topoisomerase-II (topo-II) inhibition as well as anticancer potential in some human cancer cell lines. The ease of synthesis and interesting biological activities make the present series of polyaromatic-podophyllotoxin congeners as a promising new structure for the development of new anticancer agents based on podophyllotoxin scaffold. 相似文献
198.
Lepidopteran insects show remarkable resistance to radiation and chemical stress than insects of other orders. Despite this, the antioxidant
machinery of insects of this order is poorly understood. Recently we demonstrated the significance of cytoplasmic NOS and a stronger
mitochondrial antioxidant enzyme system in the stress-resistance of Lepidopteran insects. In the present study, we hypothesize two
thioredoxin peroxidase orthologues (Sf-TPx1 and Sf-TPx2) in Lepidopteran insect Spodoptera frugiperda and demonstrate their
structural/functional features important for cellular antioxidant activity and stress resistance. Results show a higher mitochondrial
localization score (WoLFPSORT) of Sf-TPx2 (mitochondria-18.0, cytoplasm-7.0, nucleus-4.0) than its Drosophila orthologue Jafrac2
(secretory-30.0; mitochondria/nucleus/cytoplasm-no signal), which is important for antioxidant activity, and a higher cytoplasmic
localization score of Sf-TPx1 (mitochondria-no signal; cytoplasm-22.0; nucleus-3.5) than the Drosophila Jafrac1 (mitochondria-17; nucleus-
11; cytoplasm-no signal). Structural modeling data show certain motifs present in Jafrac1 and Jafrac2 that affect active site conformation
and separate cysteine residues at distances not suitable for disulphide bridge formation (5.21Å; 5.73Å). These motifs are absent in Sf-TPx1
and Sf-TPx2, yielding shorter distance (2.01Å; 2.05Å) between the cysteine residues suitable for disulphide bridge formation. Taken
together, the disulphide bridge as well as mitochondrial and cytoplasmic localization are crucial for peroxidatic activity of TPx''s. Therefore,we hypothesize
that the Spodoptera TPx''s offer potentially stronger anti-oxidant activity than that of Drosophila orthologues, and may
contribute in the high radioresistance of Lepidopteran insects. 相似文献
199.
Shreenath Prasad Deep Raj Sharma Tek Chand Bhalla 《World journal of microbiology & biotechnology》2005,21(8-9):1447-1450
Summary Forty yeast strains were screened for nitrile-hydrolysing activity. Among them Kluyveromyces thermotolerans MGBY 37 exhibited highest nitrile-hydrolysing activity (0.030 μmol/h/mg dry cell weight). This yeast contained a two-enzyme
system i.e. nitrile hydratase (NHase, EC 4.2.1.84) and amidase (EC 3.5.1.4) for the hydrolysis of nitriles/amides to corresponding
acids and ammonia. However, these enzymes had more affinity for N-heterocyclic aromatic and aromatic nitriles/amides rather than unsaturated and saturated aliphatic nitriles/amides. The NHase–amidase
activity was constitutively produced by K. thermotolerence MGBY 37. Addition of acetonitrile in the medium enhanced the production of this activity while other nitriles and amides
lowered the production of NHase–amidase activity. This organism thus exhibited two types of amidase i.e. a constitutive amidase
having affinity for N-heterocyclic aromatic, unsaturated and saturated aliphatic amides and another inducible amidase with affinity for aromatic
amides. Formamide proved to be the best inducer of the latter amidase activity. This is the first report on nitrile- and amide-hydrolysing
activity in Kluyveromyces. 相似文献
200.
Verma M Singh SK Bhushan S Sharma VK Datt P Kapahi BK Saxena AK 《Chemico-biological interactions》2008,171(1):45-56
Polyalthia longifolia is a lofty evergreen tree found in India and Sri Lanka. We are reporting first time the anticancer potential of P. longifolia leaves extract (A001) and its chloroform fraction (F002). Both inhibited cell proliferation of various human cancer cell lines in which colon cancer cells SW-620 showed maximum inhibition with IC(50) value 6.1 microg/ml. Furthermore, F002 induce apoptosis in human leukemia HL-60 cells as measured by several biological end points. F002 induce apoptotic bodies formation, DNA ladder, enhanced annexin-V-FITC binding of the cells, increased sub-G(0) DNA fraction, loss of mitochondrial membrane potential (DeltaPsi(mt)), release of cytochrome c, activation of caspase-9, caspase-3, and cleavage of poly ADP ribose polymerase (PARP) in HL-60 cells. All the above parameters revealed that F002-induced apoptosis through the mitochondrial-dependent pathway in HL-60 cells. 相似文献