Home  About us  Contact
 

Chem Soc (chem + soc)

Distribution by Scientific Domains
Chemistry100%

Kinds of Chem Soc

  • be chem soc
    		•
  • j be chem soc
    		•

    Selected Abstracts

    Structure of a human telomeric DNA sequence stabilized by 8-bromoguanosine substitutions, as determined by NMR in a K+ solution

    FEBS JOURNAL, Issue 14 2007
    Akimasa Matsugami
    The structure of human telomeric DNA is controversial; it depends upon the sequence contexts and the methodologies used to determine it. The solution structure in the presence of K+ is particularly interesting, but the structure is yet to be elucidated, due to possible conformational heterogeneity. Here, a unique strategy is applied to stabilize one such structure in a K+ solution by substituting guanosines with 8-bromoguanosines at proper positions. The resulting spectra are cleaner and led to determination of the structure at a high atomic resolution. This demonstrates that the application of 8-bromoguanosine is a powerful tool to overcome the difficulty of nucleic acid structure determination arising from conformational heterogeneity. The obtained structure is a mixed-parallel/antiparallel quadruplex. The structure of telomeric DNA was recently reported in another study, in which stabilization was brought about by mutation and resultant additional interactions [Luu KN, Phan AT, Kuryavyi V, Lacroix L & Patel DJ (2006) Structure of the human telomere in K+ solution: an intramolecular (3+1) G-quadruplex scaffold. J Am Chem Soc 128, 9963,9970]. The structure of the guanine tracts was similar between the two. However, a difference was seen for loops connecting guanine tracts, which may play a role in the higher order arrangement of telomeres. Our structure can be utilized to design a small molecule which stabilizes the quadruplex. This type of molecule is supposed to inhibit a telomerase and thus is expected to be a candidate anticancer drug. [source]

    [Fe-Fe]-hydrogenase reactivated by residue mutations as bridging carbonyl rearranges: A QM/MM study

    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2010
    Stefan Motiu
    Abstract In this work, we found aqueous enzyme phase reaction pathways for the reactivation of the exogenously inhibited [Fe-Fe]-hydrogenases by O2, or OH,, which metabolizes to H2O (Dogaru et al., Int J Quantum Chem 2008, 108; Motiu et al., Int J Quantum Chem 2007, 107, 1248). We used the hybrid quantum mechanics/molecular mechanics (QM/MM) method to study the reactivation pathways of the exogenously inhibited enzyme matrix. The ONIOM calculations performed on the enzyme agree with experimental results (Liu et al., J Am Chem Soc 2002, 124, 5175), that is, wild-type [Fe-Fe]-hydrogenase H-cluster is inhibited by oxygen metabolites. An enzyme spherical region with a radius of 8 Å (from the distal iron, Fed) has been screened for residues that prevent H2O from leaving the catalytic site and reactivate the [Fe-Fe]-hydrogenase H-cluster. In the screening process, polar residues were removed, one at a time, and frequency calculations provided the change in the Gibbs' energy for the dissociation of water (due to their deletion). When residue deletion resulted in significant Gibbs' energy decrease, further residue substitutions have been carried out. Following each substitution, geometry optimization and frequency calculations have been performed to assess the change in the Gibbs' energy for the elimination of H2O. Favorable thermodynamic results have been obtained for both single residue removal (,G,Glu374 = ,1.6 kcal/mol), single substitution (,GGlu374His = ,3.1 kcal/mol), and combined residue substitutions (,GArg111Glu;Thr145Val;Glu374His;Tyr375Phe = ,7.5 kcal/mol). Because the wild-type enzyme has only an endergonic step to overcome, that is, for H2O removal, by eliminating several residues, one at a time, the endergonic step was made to proceed spontaneously. Thus, the most promising residue deletions which enhance H2O elimination are ,Arg111, ,Thr145, ,Ser177, ,Glu240, ,Glu374, and ,Tyr375. The thermodynamics and electronic structure analyses show that the bridging carbonyl (COb) of the H-cluster plays a concomitant role in the enzyme inhibition/reactivation. In gas phase, COb shifts towards Fed to compensate for the electron density donated to oxygen upon the elimination of H2O. However, this is not possible in the wild-type enzyme because the protein matrix hinders the displacement of COb towards Fed, which leads to enzyme inhibition. Nevertheless, enzyme reactivation can be achieved by means of appropriate amino acid substitutions. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]

    Effect of silybin and its glycosides on the expression of cytochromes P450 1A2 and 3A4 in primary cultures of human hepatocytes

    JOURNAL OF BIOCHEMICAL AND MOLECULAR TOXICOLOGY, Issue 3 2005
    Pavel Kosina
    Abstract Four ,-glycosides of flavonoligan silybin, i.e. silybin ,-galactoside, silybin ,-glucoside, silybin ,-maltoside, silybin ,-lactoside were synthesized in order to improve silybin water solubility and bioavailability (K,en et al., J Chem Soc, Perkin Trans 1, 2467,2474, 1997). The presented paper deals with the effect of silybin and its synthetic ,-glycosides on the expression of two major cytochrome P450 isoforms, CYP1A2 and CYP3A4. Primary cultures of human hepatocytes were the model of choice. mRNAs were analyzed using Northern blot and P-radiolabelled probes. CYP protein content was determined by immunoblotting using specific antibodies. Silybin and its ,-glycosides do not induce expression of CYP1A2 and CYP3A4. Tested compounds did not affect inducible expression of CYP1A2 and CYP3A4 by dioxin and rifampicin, respectively, as evaluated at the level of mRNAs and proteins. Silybin and its ,-glycosides do not interfere with the expression of CYP1A2 and CYP3A4, are not likely to produce drug,drug interactions in terms of the inducibility of two important cytochromes P450. © 2005 Wiley Periodicals, Inc. J Biochem Mol Toxicol 19:149,153, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20066 [source]

    Prediction of interactiveness between small molecules and enzymes by combining gene ontology and compound similarity

    JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 8 2010
    Lei Chen
    Abstract Determination of whether a small organic molecule interacts with an enzyme can help to understand the molecular and cellular functions of organisms, and the metabolic pathways. In this research, we present a prediction model, by combining compound similarity and enzyme similarity, to predict the interactiveness between small molecules and enzymes. A dataset consisting of 2859 positive couples of small molecule and enzyme and 286,056 negative couples was employed. Compound similarity is a measurement of how similar two small molecules are, proposed by Hattori et al., J Am Chem Soc 2003, 125, 11853 which can be availed at http://www.genome.jp/ligand-bin/search_compound, while enzyme similarity was obtained by three ways, they are blast method, using gene ontology items and functional domain composition. Then a new distance between a pair of couples was established and nearest neighbor algorithm (NNA) was employed to predict the interactiveness of enzymes and small molecules. A data distribution strategy was adopted to get a better data balance between the positive samples and the negative samples during training the prediction model, by singling out one-fourth couples as testing samples and dividing the rest data into seven training datasets,the rest positive samples were added into each training dataset while only the negative samples were divided. In this way, seven NNAs were built. Finally, simple majority voting system was applied to integrate these seven models to predict the testing dataset, which was demonstrated to have better prediction results than using any single prediction model. As a result, the highest overall prediction accuracy achieved 97.30%. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010 [source]

    E230Q mutation of the catalytic subunit of cAMP-dependent protein kinase affects local structure and the binding of peptide inhibitor

    BIOPOLYMERS, Issue 6 2006
    Man-Un Ung
    Abstract The active site of the mammalian cAMP-dependent protein kinase catalytic subunit (C-subunit) has a cluster of nonconserved acidic residues,Glu127, Glu170, Glu203, Glu230, and Asp241,that are crucial for substrate recognition and binding. Studies have shown that the Glu230 to Gln mutant (E230Q) of the enzyme has physical properties similar to the wild-type enzyme and has decreased affinity for a short peptide substrate, Kemptide. However, recent experiments intended to crystallize ternary complex of the E230Q mutant with MgATP and protein kinase inhibitor (PKI) could only obtain crystals of the apo-enzyme of E230Q mutant. To deduce the possible mechanism that prevented ternary complex formation, we used the relaxed-complex method (Lin, J.-H., et al. J Am Chem Soc 2002, 24, 5632,5633) to study PKI binding to the E230Q mutant C-subunit. In the E230Q mutant, we observed local structural changes of the peptide binding site that correlated closely to the reduced PKI affinity. The structural changes occurred in the F-to-G helix loop and appeared to hinder PKI binding. Reduced electrostatic potential repulsion among Asp241 from the helix loop section and the other acidic residues in the peptide binding site appear to be responsible for the structural change. © 2005 Wiley Periodicals, Inc. Biopolymers 81: 428,439, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source]