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Biomedical subjects

W Guschlbauer

Publications and source records attributed to W Guschlbauer.

At least 55 records · Page 3Linked to original sources
PubMed1985

The effect of 2'-fluoro-2'-deoxycytidine on herpes virus growth.

The effect of 2'-fluoro-2'-deoxycytidine (dCfl) on the growth of certain viruses of the herpes type was investigated. It is shown that the compound has considerable anti-viral activity against HSV-I, HSV-II, pseudorabies virus and equine abortion virus. It has an effect comparable to that of araC and is more efficient than br5dC, but less so than acyclovir. Experiments with thymidine kinase-negative strains of HSV-I indicated that dCfl was phosphorylated by the viral kinase, and its Km appears to be low and close to that of thymidine. Density gradient centrifugation enabled us to show that dCfl was incorporated into cellular and viral DNA and RNA. The cytotoxic activity of dCfl appears to be about 10-times smaller than that of araC. Removal of the nucleoside analog, washing and replacement with deoxycytidine reversed this effect, indicating rather a cytostatic than cytotoxic effect.

Animals↗
PubMed1985

Z-DNA is formed by poly (dC-dG) and poly (dm5C-dG) at micro or nanomolar concentrations of some zinc(II) and copper(II) complexes.

We report studies on the interaction of some zinc(II) and copper(II) complexes of amines and amino acids with poly(dC-dG) and poly(dm5C-dG). Of the zinc complexes the species zinc-tris(2-aminoethyl) amine is found to be the most efficient for inducing Z-DNA giving a mid point at low ionic strength of 1.4 microM (poly(dC-dG] and 44nM (poly(dm5C-dG). While an antagonistic effect on raising the ionic strength is observed, the transition occurs at only 2 microM for poly(dm5C-dG) at 150mM NaCl. The most efficient copper(II) complex is that of diethylene triamine, though copper(II) complexes are generally less efficient than zinc(II) complexes. We also report kinetic and thermodynamic studies upon the B-Z transition induced by these complexes. A model is proposed for the interaction of one of the zinc complexes which involves not only direct zinc-DNA binding but also the formation of hydrogen bonds between the metal bond amine groups and the residues adjacent to the coordination site.

Circular Dichroism↗
PubMed1984

Helix opening in deoxyribonucleic acid from a proton nuclear magnetic resonance study of imino and amino protons in d(CG)3.

All exchangeable protons in a short DNA helix, d(CG)3 sodium salt, have been studied by proton nuclear magnetic resonance. The cytidine and guanosine amino protons have been assigned for the first time. As a function of temperature the cytidine amino protons and the imino protons behave very similarly, their relaxation is dominated by exchange with solvent above 30 degrees C. The guanosine amino protons, however, show that helix opening can only be described by a multistate model. The most rapid process observed is probably a twist about the helix axis which lengthens or breaks the guanosine amino hydrogen bond and allows rotation of the amino group. The second fastest process is a scissor opening into the major groove which gives rise to solvent exchange with the imino and cytidine amino protons. The slowest process observed is the complete base pair opening in which the guanosine amino protons also exchange with solvent. For the ammonium salt of the oligonucleotide, a specific ammonium ion complex is observed which at low temperature may catalyze exchange of the guanosine amino protons with the protons of the ammonium ion, but retards exchange with solvent. The complex appears to be specific for the sequence d(CpG).

Amines↗
PubMed1983

Interferon induction by platinum(II)-poly(I).poly(C) complexes.

The effect of the interaction between poly(I).poly(C) and cis-dichloro-diammineplatinum(II) (cis-Pt), its trans analogue and chloro-diethylene-triamminoplatinum(II) (dien-Pt) on interferon induction activity was investigated. The covalent monodentate fixation of the three compounds on N7 of inosine has different effects on the structure and thermostability of poly(I). poly(C) which is well reflected by the interferon induction activity of the samples. Thus, the sandwich stabilization by dien-Pt at low binding ratios is manifested by an increased interferon induction and a high resistance towards RNAase degradation. The destabilization of the duplex by cis-Pt decreases interferon induction, accompanied by an increase in RNAase sensitivity of the complexes. In the case of trans-Pt the duplex structure is little perturbed and interferon induction is essentially maintained.

Animals↗
PubMed1983

Chain length-dependent association of distamycin-type oligopeptides with A X T and G X C pairs in polydeoxynucleotide duplexes.

Different binding affinities of various distamycin analogs including the deformylated derivative with poly(dA-dC) X poly(dG-dT) were investigated using CD measurements. The inhibitory effect of distamycins on the DNAase I cleavage activity of DNA duplexes strongly supports the binding data. The base specificity of the ligand interaction with duplex DNA depends on the chain length of distamycin analogs. Netropsin, distamycin-2 and the deformylated distamycin-3 show no binding to dG X dC containing sequences at moderate ionic strength and are classified as highly dA X dT specific. In contrast distamycin having three, four or five methylpyrrolecarboxamide groups also forms more or less stable complexes with dG X dC-containing duplexes. These ligands possess a lower basepair specificity. The correlation between binding behavior and oligopeptide structure shows that presence of the number of hydrogen acceptor and donor sites determines the basepair and sequence specificity. The additional interaction with dG X dC pairs becomes essential when the number of hydrogen acceptor sites exceeds n = 3.

Animals↗
PubMed1983

Z-DNA and other non-B-DNA structures are reversed to B-DNA by interaction with netropsin.

The interaction between the B-form specific ligands netropsin (Nt) and distamycin-3 (Dst-3) and DNA duplexes has been studied under conditions of salt concentration and low water activity that modify the polymer conformation into a non-B DNA form, putatively a Z-like form. Three polymers with strict alternating purine-pyrimidine sequences and GC content from 100-0% have been tested: poly(dG-dC) . poly(dG-dC), poly(dA-dC) . poly(dG-dT) and poly(dA-dT) . poly(dA-dT). The titrations by Nt and Dst-3 were followed by circular dichroism. Although specific binding of Nt to the Z-form of poly(dG-dC) . poly(dG-dC) does not occur, Nt reverses this Z structure to the B-type conformation; Dst-3 is, however, totally inefficient. The presumed non-B or Z-like structure of poly(dA-dC) . poly(dG-dT) is reversed to the B-form upon interaction with Nt; Dst-3 also induces this reversal but at higher ligand ratios. The modified B-structure of poly(dA-dT) . poly(dA-dT) in low water activity is efficiently reversed to the B-form by interaction with both Nt and Dst-3.

Chemical Phenomena↗
PubMed1982

Specific interaction of netropsin, distamycin-3 and analogs with LC duplexes: reversion towards the B form of the 2'-deoxy-.2'-deoxy-2'-fluoro-hybrid duplexes upon specific interaction with netropsin, distamycin-3 and analogs.

Binding of the B-form specific ligands netropsin and distamycin-3, -4 and -5 has been used to monitor the presence and/or the inducibility of a B-type structure in various poly-inosinic.poly-cytidilic double stranded polymers with deoxyribose, ribose or 2'-deoxy-2'-fluororibose as sugar on either strand. The efficiency of binding was followed by circular dichroism and further evaluated by the increase in melting temperature of the complexes. The efficient binding of netropsin and distamycins to the hybrid polymer (dIfl)n. (dC)n demonstrated that the fluorine carrying strand may undergo a A to B-type transition reflecting a change of the 2'-deoxy-2'-fluororibose from the 3'-endo to the 1'-exo or 2'-endo pucker. The less efficient binding of the same ligands to the reverse hybrid (dI)n.(dCfl)n showed that the geometry of the pyrimidine strand is the most critical for the specific interaction. Taking into account the recent findings about the regular hydration in the minor groove of the B-type dodecamer dCGCGAATTCGCG in solid-state, the different binding modes observed between the different polymers and antibiotics are explained by differences in their possibilities of hydration. Binding of netropsin to a double stranded deoxypolymer is interpreted as a local replacement of water molecules by netropsin in the minor groove hydration network which is typical of the B-form.

Chemical Phenomena↗
PubMed1982

Differential stabilization by netropsin of inducible B-like conformations in deoxyribo-, ribo- and 2'-deoxy-2'-fluororibo-adenosine containing duplexes of (dA)n . (dT)n and (dA)n . (dU)na.

Six polynucleotide duplexes containing polydeoxyadenylic acid, polyadenylic acid or poly-2'-deoxy-2'-fluoro-adenylic acid in one strand, and polydeoxyuridylic acid or polydeoxythymidylic acid in the other strand have been studied by circular dichroism, ionic strength dependence of melting temperatures and binding of the DNA specific antibiotic netropsin. Circular dichroism spectra of (dA)n . (dT)n and (dA)n . (dU)n indicated the presence of the B-form of DNA, while those of (dAfl)n . (dT)n and (rA)n . (dT)n (and the corresponding (dU)n hybrids) indicated the presence of the A-form. (dAfl)n . (dT)n and (dAfl)n . (dU)n bound netropsin only slightly less than the (dA)n containing duplexes, while replacement by (rA)n decreased netropsin binding to a large degree. Since netropsin requires B-DNA for binding, it is concluded that the A to B transition is facilitated in the case of fluorine substitution in the sugar moiety, while the 2'-OH group greatly limits this conformational change.

Adenosine↗
PubMed1982

Polynucleotide helix geometry and stability. Spectroscopic, antigenic and interferon-inducing properties of deoxyribose-, ribose-, or 2'-deoxy-2'-fluororibose-containing duplexes of poly(inosinic acid) . poly(cytidylic acid).

Circular dichroism, absorbance temperature profiles, antigenic properties, and interferon-inducing capacity of the nine double-stranded complexes between poly(inosinic acid) and poly(cytidylic acid) [(rI)n . (rC)n] and their deoxy- and 2'-deoxy-2'-fluoro-analogues were studied. The complexes containing only ribose or 2'-fluororibose chains showed similar CD spectra and thermal stabilities. Anti-(rI)n . (rC)n antibodies were well recognized by the duplexes containing 2'-fluororibose in either one strand. These two duplexes were also efficient interferon inducers. Presence of fluororibose in both strands decreased the affinity of anti-(rI)n . (rC)n antibodies slightly and abolished interferon-inducing activity. All polydeoxyriboside-containing complexes showed CD spectra significantly different from the previous group; they showed also 40- to 100-times lower affinity for the anti-(rI)n . (rC)n antibodies, and did not induce interferon. It is concluded that the structure of (rI)n . (rC)n, an A-type helix, is little perturbed by substitution of one or both strands by 2'-fluororibose. Substitution by deoxyribose in either strand considerably changes the structure of the helices. The hybrids containing poly(deoxycytidylic acid) retain at least some of the structural features of the B-type helix poly(deoxyinosinic acid) . poly(deoxycytidylic acid).

Animals↗
PubMed1982

Conformational transitions of poly(dA-dC).poly(dG-dT) induced by high salt or in ethanolic solution.

Poly(dA-dC).poly(dG-dT) was studied by circular dichroism in the presence of high CsCl concentrations and in ethanolic solutions. This alternating purine-pyrimidine duplex may undergo two conformational transitions from a B-type to a novel structure and subsequently into an A-form. Cs+ ions or increasing ethanol concentrations induced a change of the B-type CD spectrum and an inversion of the long wavelength CD band. Lowering the temperature below 0 C or addition of small amounts of Ca++ ions were particularly potent in producing a large negative CD band. A modified B-type structure or a conversion into a left-handed Z-form is considered for this conformational transition.

Circular Dichroism↗
PubMed1981

Is Tb3+ fluorescence enhancement only due to binding to single stranded polynucleotides.

Enhancement of Tb3+ fluorescence upon binding to double-stranded ribo- and deoxyribo-duplexes was investigated. It was observed that certain double stranded ribopolynucleotides completely quenched the Tb3+ fluorescence and others did not. It is concluded that the nature of the base in the duplex is critical for this enhancement. - Polydeoxyduplexes also showed enhancement of Tb3+ fluorescence, but much higher terbium concentrations were necessary to obtain similar fluorescence signals, indicative of unspecific effects. CD spectra evidence considerable conformational changes of these duplexes, in particular poly(dG-C) . poly(dG-C( which assumes the Z-form in 0.1 nM Tb3+.

Kinetics↗
PubMed1980

Conformational analysis of ribonucleosides from proton-proton coupling constants.

A graphical method is described which permits the determination in solution of conformational equilibria and parameters of ribonucleosides from proton-proton coupling constants. The method is based on the pseudorotational concept and the use of the Karplus equation. Using a large number of 1H-NMR data on ribonucleosides from the literature, on optimal set of Karplus constants, A = 10.0, B = -1.2, was obtained. It is shown that this set of Karplus constants, in connection with the pseudorotational treatment, describes satisfactorily the nucleoside conformations, especially the pucker amplitude. The solution results are compared with X-ray data and the differences are discussed. The method can be used either graphically or by direct computer treatment of the data.

Magnetic Resonance Spectroscopy↗
PubMed1980

Refolding of reduced short neurotoxins: circular dichroism analysis.

The four disulfide bonds of nine homologous short curare-like polypeptides are cleaved by reduced dithiothreitol. Air oxidation renaturations of the reduced compounds are followed by far-ultraviolet circular dichroism analysis, and the kinetics of refolding thus determined are compared. They indicate that three toxins refold 4--10 times more slowly than the six others. It is shown that a significant difference between the refolding kinetics still subsists when renaturations are made in the presence of various concentrations of thiol-disulfide exchange reagents or at various pH values. From an examination of the toxin sequences, it is proposed that a single additional amino acid insertion is responsible for the difference in the observed kinetics. This proposal is supported by temperature studies of renaturation kinetics.

Animals↗
PubMed1980

Magnetic circular dichroism study of the binding of netropsin and distamycin A with DNA.

The magnetic circular dichroism (MCD) of netropsin and distamycin-A is reported. New data for the interaction with dA ; dT base pairs in DNA were obtained from the MCD of their complexes with DNA duplex polymers. The MCD results allow an interpretation of the induced Cotton effects in the natural CD spectra of netropsin and distamycin-A complexes with DNA. While large distortions of the bases in DNA by the oligopeptide interaction is excluded, some subtle conformational variations of the DNA might explain the inhibition of the enzyme function of netropsin and distamycin-A on DNA.

Circular Dichroism↗