Raman Spectroscopic Study of the Conformation and Melting of Poly(dG) · Poly(dC) and Poly(dG-dC) · Poly(dG-dC) in Aqueous Solution

Raman spectroscopic measurements on aqueous solutions of poly(dG) · poly(dC)indicate that the conformation of the polynucleotides in this double helicalcomplex are distributed between the A and B types at room temperature, the Aform being predominant at –15°C and decreasing progressively upon raising thetemperature to 65°C. A reversible pretransition has been found in this complexnear 70°C. Modifications in the spectra at this temperature indicate no majorconformational changes, but rather suggest altered base pairing and hydration ofthe carbonyl groups, accompanied by a slight distortion of the double helix,resulting in a slightly reduced stacking of the cytosine bases. Measurements inself-pressurized solutions of the complex at high temperature show that it meltsat 103°C in 0.1M NaCl solution (107°C in 0.5M NaCl). These values are somewhatlower than those we have determined in the same manner for the complexpoly(dG-dC) · poly(dG-dC): 117°C in 0.1M MgCl₂ and 113°C or higher in 0.1MNaCl solution.     

Engineering the Donor Selectivity of D‐Fructose‐6‐Phosphate Aldolase for Biocatalytic Asymmetric Cross‐Aldol Additions of Glycolaldehyde

D ‐Fructose‐6‐phosphate aldolase (FSA) is a unique catalyst for asymmetric cross‐aldol additions of glycolaldehyde. A combination of a structure‐guided approach of saturation mutagenesis, site‐directed mutagenesis, and computational modeling was applied to construct a set of FSA variants that improved the catalytic efficiency towards glycolaldehyde dimerization up to 1800‐fold. A combination of mutations in positions L107, A129, and A165 provided a toolbox of FSA variants that expand the synthetic possibilities towards the preparation of aldose‐like carbohydrate compounds. The new FSA variants were applied as highly efficient catalysts for cross‐aldol additions of glycolaldehyde to N‐carbobenzyloxyaminoaldehydes to furnish between 80–98 % aldol adduct under optimized reaction conditions. Donor competition experiments showed high selectivity for glycolaldehyde relative to dihydroxyacetone or hydroxyacetone. These results demonstrate the exceptional malleability of the active site in FSA, which can be remodeled to accept a wide spectrum of donor and acceptor substrates with high efficiency and selectivity.     

Protein phosphatase 2a (PP2A) binds within the oligomerization domain of striatin and regulates the phosphorylation and activation of the mammalian Ste20-Like kinase Mst3

Background

The repertoire of the antigen-binding receptors originates from the rearrangement of immunoglobulin and T-cell receptor genetic loci in a process known as V(D)J recombination. The initial site-specific DNA cleavage steps of this process are catalyzed by the lymphoid specific proteins RAG1 and RAG2. The majority of studies on RAG1 and RAG2 have focused on the minimal, core regions required for catalytic activity. Though not absolutely required, non-core regions of RAG1 and RAG2 have been shown to influence the efficiency and fidelity of the recombination reaction.

Results

Using a partial proteolysis approach in combination with bioinformatics analyses, we identified the domain boundaries of a structural domain that is present in the 380-residue N-terminal non-core region of RAG1. We term this domain the Central Non-core Domain (CND; residues 87-217).

Conclusions

We show how the CND alone, and in combination with other regions of non-core RAG1, functions in nuclear localization, zinc coordination, and interactions with nucleic acid. Together, these results demonstrate the multiple roles that the non-core region can play in the function of the full length protein.     

An easy sol–gel route for deposition of oriented Ln2Ti2O7 (Ln=La,Nd) films on SrTiO3 substrates

The effect of the orientation of SrTiO₃ (STO) substrates, (1 0 0) or (1 1 0), on the growth of La₂Ti₂O₇ (LTO) and Nd₂Ti₂O₇ (NTO) thin films was investigated. The films were deposited via a sol–gel process coupled to the spin-coating technique. Depending on the substrate orientation, a similar effect was observed on the structural properties for both the LTO and NTO thin films. For (1 1 0)-oriented STO substrate, the films are preferentially (0 0 1) oriented while for (1 0 0)-oriented STO substrates, the orientation is mainly (0 1 2). Those matching appear to be in good agreement with the compatibility between the film/substrate crystal lattices, in relation with the existence of perovskite slabs in Ln₂Ti₂O₇ (Ln=rare earth) compounds. In these latter, a slight disorientation of the (0 1 2) planes with respect to the surface of the substrate was measured. This tilting is even more marked in the case of NTO. The surface morphology was studied by atomic force microscopy.     

Dendrimers as guests in molecular recognition phenomena

Dendrimers are highly branched macromolecules which may engage in host-guest interactions, acting as either hosts or guests; this review is specifically concerned with the binding behavior of dendrimers containing single or multiple guest residues interacting with individual, freely diffusing hosts.     

High molecular weight supramolecular polymers containing both terpyridine metal complexes and ureidopyrimidinone quadruple hydrogen-bonding units in the main chain

Using a hydroxy-functionalized terpyridine as initiator, a poly(epsilon-caprolactone) containing one terpyridine endgroup was prepared by tin octanoate-catalyzed controlled ring-opening polymerization. The omega-hydroxy group of this polymer was subsequently reacted with an isocyanato-ureidopyrimidinone, resulting for the first time in polymers bearing a metal-coordinating ligand on the one and a hydrogen-bonding unit on the other chain end. Hydrogen-bonded supramolecular dimers were shown to be present in chloroform solution. The subsequent addition of iron(II) ions resulted in the formation of high molecular weight supramolecular polymers with novel properties resulting from the combination of both types of noncovalent interactions in the main chain, as could be shown using capillary viscosimetry and rheometry.     

Prodrugs of HIV protease inhibitors-saquinavir, indinavir and nelfinavir-derived from diglycerides or amino acids: synthesis, stability and anti-HIV activity

With the aim of improving the pharmacological properties of current protease inhibitors (PIs), the synthesis of various acyl and carbamate amino acid- or diglyceride-containing prodrugs derived from saquinavir, indinavir and nelfinavir, their in vitro stability with respect to hydrolysis and their anti-HIV activity in CEM-SS and MT4 cells have been investigated. l-Leucine (Leu) and l-phenylalanine (Phe) were connected through their carboxyl to the PIs while l-tyrosine (Tyr) was conjugated through its aromatic hydroxyl via various spacer units. Hydrolysis of the prodrug with liberation of the active free drug was crucial for antiviral activity. The Leu- and Phe-PI prodrugs released the active free drug very rapidly (half-lives of hydrolysis in buffer at 37 degree C of 3-4 h). The Tyr-PI conjugates with a -C(O)(CH(2))(4)- linker exhibited half-lives in the 40-70 h range and antiviral activities in the 21-325 nM range (from 2 to 22 nM for the free PIs). The chemically very stable carbamate "peptidomimetic" Tyr-PI prodrugs (no hydrolysis detected after 7 days in buffer) displayed a very low anti-HIV activity or were even inactive (EC(50) from 2300 nM to >10 microM). A very low antiviral activity was measured for the diglyceride-substituted saquinavir and for all of the disubstituted indinavir and nelfinavir prodrugs. All these prodrugs probably released the active parent PI too slowly under the antiviral assay conditions. These results combined with those from transepithelial transport studies (Rouquayrol et al., Pharm. Res., 2002, 19, 1704-1712) indicate that conjugation of amino acids (through their carboxyl) to the PIs constitutes a most appealing alternative which could improve the intestinal absorption of the PIs and reduce their recognition by efflux carriers.     

THE EFFECT OF TEMPERATURE AND WAVELENGTH ON PRODUCTION AND PHOTOLYSIS OF A UV-INDUCED PHOTOSENSITIVE DNA LESION WHICH IS NOT REPAIRED IN XERODERMA PIGMENTOSUM VARIANT CELLS

Abstract— Ultraviolet light causes a type of damage to the DNA of human cells that results in a DNA strand break upon subsequent irradiation with wavelengths around 300 nm. This DNA damage disappears from normal human fibroblasts within 5 h, but not from pyrimidine dimer excision repair deficient xeroderma pigmentosum group A cells or from excision proficient xeroderma pigmentosum variant cells. The apparent lack of repair of the ultraviolet light DNA damage described here may contribute to the cancer prone nature of xeroderma pigmentosum variant individuals. These experiments show that the same amount of damage was produced at 0^°C and 37^°C indicating a photodynamic effect and not an enzymatic reaction. The disappearance of the photosensitive lesions from the DNA is probably enzymatic since none of the damage was removed at 0^°C. Both the formation of the lesion and its photolysis by near ultraviolet light were wavelength dependent. An action spectrum for the formation of photosensitive lesions was similar to that for the formation of pyrimidine dimers and(6–4) photoproducts and included wavelengths found in sunlight. The DNA containing the lesions was sensitive to wavelengths from 304 to 340 nm with a maximum at 313 to 317 nm. This wavelength dependence of photolysis is similar to the absorption and photolysis spectra of the pyrimidine(6–4) photoproducts     

Zirconium-substituted isopolytungstates: structural models for zirconia-supported tungsten catalysts

The synthesis and characterization of a series of mixed W-Zr polynuclear Lindqvist-type complexes, deriving from hexatungstate [W6O19]2-, are described in this work. This family of compounds is built from {W5O18Zr}2- moieties as shown by the X-ray structures of the monomeric [W5O18Zr(H2O)(3-n)(DMSO)n]2- (n = 1 and 2) and dimeric [{W5O18Zr(mu-OH)}2]6- anions. A comprehensive spectroscopic study (183W NMR, FTIR, Raman, EXAFS, and EPR) of these compounds is presented. The goal of incorporating Zr(IV) cations into an oxotungstic core is to obtain spectroscopic models that could mimic the interactions that develop in supported catalysts between the active phase and the supporting oxide. This work tends to show that these molecular compounds can be regarded as soluble structural analogues of WOx/ZrO2 catalysts, which are interesting candidates for the skeletal isomerization of light n-alkanes.