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Cyclic Phosphate (cyclic + phosphate)
Selected AbstractsOrganosulfur- or Organoselenium-Induced Intramolecular Cycloaddition of ,-Allenic ,-Difluoromethylenephosphonic Acid Monoesters: Synthesis of Novel Cyclic Phosphate Mimics.CHEMINFORM, Issue 1 2007Yun Lin Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Structures of apo and GTP-bound molybdenum cofactor biosynthesis protein MoaC from Thermus thermophilus HB8ACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Shankar Prasad Kanaujia The first step in the molybdenum cofactor (Moco) biosynthesis pathway involves the conversion of guanosine triphosphate (GTP) to precursor Z by two proteins (MoaA and MoaC). MoaA belongs to the S -adenosylmethionine-dependent radical enzyme superfamily and is believed to generate protein and/or substrate radicals by reductive cleavage of S -adenosylmethionine using an Fe,S cluster. MoaC has been suggested to catalyze the release of pyrophosphate and the formation of the cyclic phosphate of precursor Z. However, structural evidence showing the binding of a substrate-like molecule to MoaC is not available. Here, apo and GTP-bound crystal structures of MoaC from Thermus thermophilus HB8 are reported. Furthermore, isothermal titration calorimetry experiments have been carried out in order to obtain thermodynamic parameters for the protein,ligand interactions. In addition, molecular-dynamics (MD) simulations have been carried out on the protein,ligand complex of known structure and on models of relevant complexes for which X-ray structures are not available. The biophysical, structural and MD results reveal the residues that are involved in substrate binding and help in speculating upon a possible mechanism. [source] Crystallization and preliminary crystallographic studies of putative RNA 3,-terminal phosphate cyclase from the crenarchaeon Sulfolobus tokodaiiACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 6 2009Satoru Shimizu RNA 3,-terminal phosphate cyclase (Rtc) is an enzyme involved in RNA splicing that converts the 3,-terminal hydroxyl group of truncated RNA to 2,,3,-cyclic phosphate, which is required just before its ligation. This reaction may occur in the following two steps: (i) Rtc + ATP , Rtc-AMP + PPi and (ii) RNA-N3,p + Rtc-AMP , RNA-N>p + Rtc + AMP. In order to reveal the reaction mechanism, Rtc of Sulfolobus tokodaii (St -Rtc) overexpressed in Escherichia coli was purified and crystallized in the following states: St -Rtc, St -Rtc+Mn, St -Rtc+ATP, St -Rtc+AMP and St -Rtc-AMP. The crystals diffracted to 2.25,3.00,Å resolution and preliminary solutions of their structures have been obtained by molecular replacement using the structure of a selenomethionine-labelled St -Rtc crystal which was solved in advance using the MAD method as a model. These crystals grew in two different space groups (P31 and P42), with the former space group displaying two distinct packing modes. [source] Reaction of Cytidine Nucleotides with Cyanoacetylene: Support for the Intermediacy of Nucleoside-2,,3,-cyclic Phosphates in the Prebiotic Synthesis of RNACHEMBIOCHEM, Issue 6 2006Michael A. Crowe Abstract A robust and prebiotically plausible synthesis of RNA is a key requirement of the "RNA World" hypothesis, but, to date, no such synthesis has been demonstrated. Monomer synthesis strategies involving attachment of preformed nucleobases to sugars have failed, and, even if activated 5,-nucleotides could be made, the hydrolysis of these intermediates in water makes their efficient oligomerisation appear unlikely. We recently reported a synthesis of cytidine-2,,3,-cyclic phosphate 1 (C>p) in which the nucleobase was assembled in stages on a sugar-phosphate template. However, 2,,3,-cyclic nucleotides (N>p's) also undergo hydrolysis, in this case giving a mixture of the 2,- and 3,-monophosphates. This hydrolysis has previously been seen as making the, otherwise promising, oligomerisation of N>p's seem as unlikely as that of the 5,-activated nucleotides. We now find that cyanoacetylene, the reagent used for the second stage of nucleobase assembly in the synthesis of C>p, also reverses the effect of the hydrolysis by driving efficient cyclisation of C2,p and C3,p back to C>p. Excess cyanoacetylene also derivatises the nucleobase, but this modification is reversible at neutral pH. These findings significantly strengthen the case for N>p's in a prebiotic synthesis of RNA. [source] | ||||||||||