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G Lancelot

Publications and source records attributed to G Lancelot.

At least 37 records · Page 2Linked to original sources
PubMed1988

Proton magnetic resonance studies of the binding of oligopeptides containing tryptophan to polyribonucleotides poly A, poly U and poly C.

The binding of oligopeptides Lys-Trp-Gly-Lys OtBu, Lys-Gly-Trp-Lys OtBu and Lys-Trp-Lys to Polyadenylic, Polycytidylic and Polyuridylic acid has been studied by Proton NMR at 90 MHz and 500 MHz at oligopeptide/Polynucleotide ratios ranging from 0.01 to 0.20 at 275-365 K. Downfield shift of 0.01-0.2 ppm at 296 K of the H2, H8 and H1' resonances of Poly A due to binding with oligopeptides is accompanied by a marked narrowing of resonance lines of Poly A. The ring protons of tryptophan shift upfield by 0.3-0.6 ppm at 296 K on binding to Poly A. Changes in chemical shift of both adenine and tryptophan protons on binding are much smaller at 355 K than that at 275 K. These observations are ascribed to intercalation of the tryptophan ring in the adenine bases resulting in partial destacking of adenine bases in Poly A. Using the magnetic anisotropy ring current shifts, an overlap geometry of tryptophan ring in the adenine has been proposed. Addition of oligopeptides to Poly C and Poly U, on the other hand, suggests that tryptophan ring does not stack in Poly U and Poly C.

Magnetic Resonance Spectroscopy↗
PubMed1987

2D-NMR studies of the unnatural duplex alpha-d(TCTAAAC)-beta-d(AGATTTG).

The unnatural oligonucleotide alpha-d(TCTAAAC) was synthesized and was found more resistant towards endonucleases than its beta-analog. 2D-NMR experiments allowed the assignment of all non-exchangeable aromatic and sugar protons except for the overlapping 5' -5" resonances, as well as the exchangeable imino protons of the parallel hybrid duplex alpha-d (TCTAAAC)-beta-d(AGATTTG). NMR studies show that the strength of the association between the alpha-strand and the beta parallel strand is equivalent to that between their anti-parallel complementary beta-analogs beta-d(CAAATCT) and beta-d(AGATTTG). NOE data provide evidence that both duplexes form stable right-helical duplexes with an anti-conformation on the glycosyl linkages and a Watson-Crick pairing. NOESY and COSY spectra allowed us to determine that alpha and beta deoxyriboses adopt a 3' -exo conformation.

Base Sequence↗
PubMed1986

Nuclear magnetic resonance studies of complex formation between the oligonucleotide d(TATC) covalently linked to an acridine derivative and its complementary sequence d(GATA).

The oligodeoxynucleotide d(TATC) was covalently attached to the 9-amino group of 2-methoxy-6-chloro-9-aminoacridine (Acr) through its 3'-phosphate via a pentamethylene linker (m5). Complex formation between d(TATC)m5Acr and the complementary strand d(GATA) in aqueous solution was investigated by nuclear magnetic resonance. The COSY and NOESY connectivities allowed us to assign all the proton resonances of the bases, the sugars (except the overlapping 5'/5'' resonances), the acridine, and the pentamethylene chain. Structural informations derived from relative intensities of COSY and NOESY maps revealed that the duplex d(TATC)-d(GATA) adopts a B-type conformation and that the deoxyriboses preferentially adopt a 2'-endo conformation. The NOE connectivities observed between the protons of the bases or of the sugars and the protons of the dye and of the pentamethylene chain led us to propose a model involving an equilibrium between two families of configurations. In the first family, the acridine derivative is intercalated between base pairs C4-G4 and T3-A3. In the second family, the acridine derivative is sandwiched between two aggregated duplexes. The structure of the intercalated complex as well as that of the aggregated species is discussed.

Acridines↗
PubMed1986

31P NMR studies of the binding of the oligonucleotide (Ap)3A to an oligodeoxythymidylate covalently linked to an acridine derivative.

31P NMR was used to study the specific interaction of an oligodeoxynucleotide containing four thymines and covalently attached to an acridine derivative through its 3'-phosphate [(Tp)4(CH2)5Acr] with a complementary oligoribonucleotide (Ap)3A. 31P-1H and 1H-1H chemical shift correlation spectroscopies were jointly used to provide the assignment of the phosphorus resonances. A downfield shift of two phosphorus resonances of (Tp)4(CH2)5Acr and of two phosphorus resonances of (Ap)3A was observed upon complex formation. The assignment of the phosphorus resonances which are downfield shifted allowed us to propose a model involving an equilibrium between several 1:1 complexes where the acridine ring is intercalated between different A.T base pairs.

Acridines↗
PubMed1985

Proton and phosphorus nuclear magnetic resonance studies of an oligothymidylate covalently linked to an acridine derivative and of its binding to complementary sequences.

An oligodeoxynucleotide containing four thymines and covalently attached to an acridine derivative through its 3'-phosphate [(Tp)4(CH2)5Acr] was synthesized. Its conformation in solution was investigated by proton magnetic resonance. Both intramolecular interactions between the acridine dye and thymines and intermolecular interactions were demonstrated. Both proton and phosphorus magnetic resonances were used to study the specific interaction of (Tp)4(CH2)5Acr with poly(rA) and (Ap)3A. The results were compared to those obtained when the acridine-containing substituent was replaced by an ethyl group attached to the 3'-phosphate of the oligothymidylate. The acridine dye strongly stabilized the complexes formed with both poly(rA) and (Ap)3A. Upfield shifts of both adenine and acridine proton resonances were observed in the complexes. These results were ascribed to an intercalation of the acridine ring between A X T base pairs of the duplex structure formed by the oligothymidylate with its complementary oligoadenylate sequence. An analysis of proton and phosphorus chemical shifts as well as measurements of T1 relaxation times at different temperatures allowed us to propose several structures for the complexes formed by (Tp)4(CH2)5Acr with its complementary sequence.

Adenine Nucleotides↗
PubMed1984

Phosphate-guanosine interactions. A model for the involvement of guanine derivatives in autocatalytic reactions of ribonucleic acids.

Proton magnetic resonance was used to study the interactions between nucleosides and phosphate monoanion in dimethyl sulfoxide. Ribose was able to form two mutually exclusive 1:1 complexes involving either OH3' and OH5' or OH3' and OH2' as hydrogen bond donor groups. Deoxyribose could form only one of these complexes. A specific interaction of phosphate with the base moiety of nucleosides was observed only with guanosine. A 1:1 complex was formed involving the N(1)H and NH2(2) of guanine. Association constants for both the base and sugar complexes were determined to be in the range 50-60 M-1 at 21 degrees C in dimethyl sulfoxide. This value is more than 1 order of magnitude higher than that measured for guanine-cytosine base pair formation under the same conditions. Water addition to dimethyl sulfoxide led to a decrease of all association constants but the guanine-phosphate "pair" remained more stable than the guanine-cytosine base pair.

Adenine↗
PubMed1984

Sequential assignment of the 1H and 31P resonances of the double stranded deoxynucleotide d (ATGCAT)2 by 2D-NMR correlation spectroscopy.

31p-1H and 1H-1H chemical shift correlation spectroscopy are jointly used for providing a complete assignment of sugar proton (except H5' and H5") and phosphorus resonances in the double stranded oligonucleotide d (ATGCAT)2. In contrast to previous methods the specific assignment of overcrowded H5' H5" proton resonances is not required. Using the H3'-P coupling and also the long range H4'-P coupling, this quite general method can be easily implemented on intermediate field spectrometer. The present results pave the way to the 1H and 31P resonance assignment of longer double-stranded oligonucleotides.

Deuterium↗
PubMed1984

Nucleic acid-binding molecules with high affinity and base sequence specificity: intercalating agents covalently linked to oligodeoxynucleotides.

Oligodeoxyribonucleotides covalently linked to an intercalating agent via a polymethylene linker were synthesized. Oligothymidylates attached to an acridine dye (Acr) through the 3'-phosphate group [(Tp)n(CH2) mAcr ] specifically interact with the complementary sequence. The interaction is strongly stabilized by the intercalating agent. By using absorption and fluorescence spectroscopies, it is shown that complex formation between (Tp)n(CH2) mAcr and poly(rA) involves the formation of n A X T base pairs, where n is the number of thymines in the oligonucleotide. The acridine ring intercalates between A X T base pairs. Fluorescence excitation spectra reveal the existence of two environments for the acridine ring, whose relative contributions depend on the linker length (m). The binding of (Tp)4(CH2) mAcr to poly(rA) is analyzed in terms of site binding and cooperative interactions between oligonucleotides along the polynucleotide lattice. Thermodynamic parameters show that the covalent attachment of the acridine ring strongly stabilizes the binding of the oligonucleotide to its complementary sequence. The stabilization depends on the linker length; the compound with m = 5 gives a more stable complex than that with m = 3. These results open the way to the synthesis of a family of molecules exhibiting both high-affinity and high-specificity for a nucleic acid base sequence.

Acridines↗
PubMed1983

Interactions of the 26-39 fragment of the cro protein from lambda bacteriophage with nucleic acids.

A tetradecapeptide with a sequence identical to residues 26-39 of the cro protein from bacteriophage lambda has been synthesized. This peptide has no secondary structure in an aqueous buffer but adopts an alpha-helical conformation in the presence of 20% hexafluoroisopropanol. The fluorescence of the single tyrosyl residue of the cro protein fragment is quenched upon binding to nucleic acids. Proton magnetic resonance has been used to investigate complex formation of the cro protein fragment with a self-complementary decadeoxynucleotide d(AATTGCAATT). Changes in resonance positions and linewidths have been observed for both partners in the 4 complexes which are obtained when either the single-stranded or double-stranded oligonucleotide is mixed with either the random coil or the alpha-helical peptide. These studies are presently extended to the specific complex formed by the cro protein fragment with the OR3 operator sequence.

Bacteriophage lambda↗
PubMed1981

Synthesis and structural studies of a self-complementary decadeoxynucleotide d(AATTGCAATT). I.-Synthesis and chemical characterization of the decanucleotide.

The synthesis of the self-complementary decadeoxynucleotide d(AATTGCAATT) is described. The phosphotriester method has been used with several modifications. Protected nucleotides have been prepared in a one-step reaction involving a new monofunctional phosphorylating agent: p-chlorophenyl-beta-cyanoethyl phosphate. Triethylammonium salts of mononucleoside 3'-phosphodiesters were obtained either by decyanoethylation of the triesters or, in the case of thymine, by a one-step reaction starting from 5'-0-methoxytritylthymidine and the mixture pyridine-para-chlorophenyl-methyl-phosphorobromidate. The usual coupling reactions were then used to prepare the decadeoxynucleotide in large quantities.

Chemical Phenomena↗
PubMed1981

Synthesis and structural studies of a self-complementary decadeoxynucleotide d(AATTGCAATT). II.-Proton magnetic resonance studies.

Proton magnetic resonance spectra of the self-complementary decadeoxynucleotide d(AATTGCAATT) at 90 and 250 MHz have been obtained at different temperatures. The assignment of the different resonance lines to the base protons was obtained by combining the data derived from various methods: hydrogen in equilibrium with deuterium exchange at the H8 position of purines; comparison of NMR spectra obtained at high temperature with those of mononucleotides; comparison of the variations in chemical shifts obtained between 280 K and 360 K with calculated values; determination of half-transition temperatures for each base pair. On the basis of computed chemical shifts for stacked base-pairs it is concluded that the decadeoxynucleotide duplex exists in the B form in solution at 280 K. Propagation of the opening of the mini double helix from terminal to central base pairs if reflected in the variation of half-transition temperatures which vary between 306 K and 327 K.

Chemical Phenomena↗
PubMed1979

Models of interaction between nucleic acids and proteins. Hydrogen bonding of arginine with nucleic acid bases, phosphate groups and carboxylic acids.

Complex formation between the side chain of arginine and nucleic acid bases has been investigated by proton magnetic resonance in dimethylsulfoxide. Simultaneous formation of two hydrogen bonds leads to a selectivity of arginine interaction towards cytosine and guanine. A comparison is made of the interaction of arginine side chain with nucleic acid bases, phosphate and carboxylate anions. It is shown that interaction between carboxylate and arginine is stronger than between phosphate and arginine. These results are discussed with respect to the selective recognition of nucleic acid bases by arginine side chains and by the arginyl-glutamyl ion pair which could form in proteins interacting with nucleic acids.

Arginine↗
PubMed1979

Model studies of interactions between nucleic acids and proteins: hydrogen bonding of amides with nucleic acid bases.

The formation of hydrogen bonded complexes between nucleic acid bases and acetamide has been studied by nuclear magnetic resonance in CDC13 at different temperatures. Pairs of hydrogen bonds are formed when acetamide binds to nucleic acid bases. Thermodynamic parameters have been computed and compared to those obtained for the association of carboxylic acids with nucleic acid bases. The role of hydrogen bonded complexes in the association of proteins with nucleic acids is discussed.

Acetamides↗
PubMed1977

Hydrogen bonding of adenine derivatives to tyrosine side chain.

High resolution proton magnetic resonance measurements provide evidence for the formation of hydrogen-bonded complexes between 9-ethyladenine and p-cresol used as a model of tyrosine side chain in CDCl3. We have calculated the sum of the association constants corresponding to the three existing 1:1 complexes: K=6.3+/-0.15. By methylation of the amino group of adenine, we were able to calculate the ratio of the two strongest equilibrium constants K7/K1=1.6+/-0.3. Theoretical computations by the complete neglect of differential overlap (CNDO/2) method indicate that several hydrogen-bonded planar complexes can form between 9-methyladenine and phenol. The computed energy of the complexes with 6-dimethylamino adenine removes some ambiguity concerning the computed ratio of the association constants. Comparison of the calculated energies with free energies experimentally determined in organic solvent shows that despite the competition with CDCl3, which associates with both solute molecules, the preferential order of association is conserved. The small variations of charge density of adenine carbon atoms when complexed with phenol are in agreement with very small chemical shifts observed by 13C-nuclear magnetic resonance.

Adenine↗
PubMed1977

Hydrogen bonding of amino acid side chains to nucleic acid bases.

Absorption studies of hydrogen bonding association between nucleic acid bases and amino acid side chains show that association constants can be determined from difference absorption spectra in cyclohexane and chloroform. Association constants for the binding of 9-ethyladenine, 1-cyclohexyluracil and 1-cyclohexylcytosine to side chains of serine, threonine, aspartic acid, lysine, cystéine, methionine and tyrosine are reported. Results obtained in chloroform and cyclohexane are compared.

Amino Acids↗