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Biomedical subjects

C Helene

Publications and source records attributed to C Helene.

At least 37 records · Page 2Linked to original sources
PubMed1985

Molecular mechanisms for the recognition of damaged DNA regions by peptides and proteins.

DNA damages can lead to drastic perturbations of living cell cycle (e.g., in carcinogenesis) by inducing mutations in the genetic information. Therefore DNA repair processes play an important role during cell life by eliminating DNA damages before mutation fixation. Different repair processes are briefly presented in this review. Two probes were used to provide information on the mechanisms involved in the specific recognition of damaged DNA by proteins and enzymes of the DNA repair machinery. It will be shown that a simple tripeptide Lys-Trp-Lys is able to mimic two repair systems, namely, the photosensitized splitting of pyrimidine dimers and the cleavage of phosphodiester bonds at apurinic sites.

DNA↗
PubMed1984

Interaction of a tryptophan-containing peptide with chromatin core particles. A fluorescence study.

The binding of a tetrapeptide lysyltryptophylglycyllysine to nucleosome core particles has been investigated using UV absorption and fluorescence spectroscopy. Modifications of the absorption spectra and fluorescence quenching of the tryptophyl residue are consistent with stacking between the indole ring and nucleic acid bases. Therefore DNA interactions with histones do not prevent stacking of the tryptophyl residue with nucleic acid bases in the peptide-core particle complexes. The number of peptide binding sites is reduced to half that of naked DNA.

Animals↗
PubMed1984

Absorption and fluorescence studies of the binding of the recA gene product from E. coli to single-stranded and double-stranded DNA. Ionic strength dependence.

The binding of the recA gene product from E. coli to double-stranded and single-stranded nucleic acids has been investigated by following the change in melting temperature of duplex DNA and the fluorescence of single-stranded DNA or poly(dA) modified by reaction with chloroacetaldehyde. At low ionic strength, in the absence of Mg2+ ions, RecA protein binds preferentially to duplex DNA or poly(dA-dT). This leads to an increase of the DNA melting temperature. Stabilization of duplex DNA decreases when ionic strength or pH increases. In the presence of Mg2+ ions, preferential binding to single-stranded polynucleotides is observed. Precipitation occurs when duplex DNA begins to melt in the presence of RecA protein. From competition experiments, different single-stranded and double-stranded polydeoxynucleotides can be ranked according to their ability to bind RecA protein. Structural changes induced in nucleic acids upon RecA binding are discussed together with conformational changes induced in RecA protein upon magnesium binding.

DNA↗
PubMed1983

Excitation energy transfer from tryptophan residues of peptides and intrinsic proteins to diphenylhexatriene in phospholipid vesicles and biological membranes.

An efficient excitation energy transfer from tryptophan residues of intrinsic membrane proteins to an extrinsic fluorescent probe (diphenylhexatriene) has been demonstrated in rat erythrocyte ghosts. To correlate this transfer with the localization of the probe, a model system has been investigated. It consists of peptides containing lysine and tryptophan residues bound to negatively charged phosphatidylserine vesicles. Absorption and fluorescence spectroscopies were used to follow peptide binding and diphenylhexatriene incorporation. Peptide binding is accompanied by a blue shift of the tryptophan fluorescence together with an increase of the quantum yield and of the fluorescence decay time. An experimental Föster critical distance value of 4.0 nm was found for energy transfer from tryptophan residues of peptides to diphenylhexatriene which approaches the range of calculated values (3.1-3.7 nm) using a two-dimensional model. These results demonstrate that efficient energy transfer can occur from tryptophan residues of intrinsic proteins to diphenylhexatriene without any interaction between diphenylhexatriene and proteins in biological membranes.

Animals↗
PubMed1982

Diffuse structural alterations in cell membranes of spontaneously hypertensive rats.

Plasma membranes from heart, nerve endings, and liver were compared in 3-week-old male spontaneously hypertensive rats from the Okamoto substrain (SHR) and normotensive Wistar/Kyoto control rats (WKY) [systolic blood pressure 105 +/- 4 and 95 +/- 4 mm Hg, respectively (1 mm Hg = 133 Pa)] according to two criteria: calcium binding at physiological intracellular concentrations and polarization of an embedded fluorescent probe, 1,6-diphenyl-1,3,5-hexatriene. Whatever the tissue of origin, the density of high-affinity calcium binding sites was lower in SHR than in WKY plasma membranes, and the polarization of diphenylhexatriene fluorescence was constantly higher in SHR than in WKY membranes. These membrane abnormalities are similar to those previously described in the erythrocyte membrane from SHR. The presence of diffuse structural alterations in cellular membrane from young spontaneously hypertensive rats when blood pressure is still in the normotensive range suggests a genetic origin. Such inherited abnormalities may by themselves participate in the rise in blood pressure.

Animals↗
PubMed1981

Specific recognition of apurinic sites in DNA by a tryptophan-containing peptide.

We have used fluorescence spectroscopy to study the binding of lysyltryptophyl-alpha-lysine (Lys-Trp-Lys) to DNA modified by dimethyl sulfate before and after depurination and strand breakage. Quenching of tryptophan fluorescence increased upon association of the peptide with modified DNA as compared with native DNA. We have demonstrated that this quenching is related to a preferential stacking of the indole ring with nucleic acid bases in damaged regions. Stacking increased in the following order: methylated DNA less than DNA with strand breaks at apurinic sites much less than apurinic DNA. For apurinic DNA, the overall association constant of Lys-Trp-Lys was increased by more than two orders of magnitude as compared to native DNA. Enhancement of the affinity of the tripeptide for an apurinic site requires the integrity of the phosphodiester bond. Single-strand cleavage at an apurinic site leads to a marked decrease of the association constant. The peptide Lys-Trp-Lys is therefore able to recognize destabilized regions in the vicinity of a lesion and to discriminate between different configurations of the damaged region. These results are discussed with respect to the role that stacking interactions could play in the specificity of recognition of DNA alterations by enzymes involved in DNA repair mechanisms.

Apurinic Acid↗
PubMed1979

A spectroscopic probe of stacking interactions between nucleic acid bases and tryptophan residues of proteins.

The external heavy atom effect of mercury on the spectroscopic properties of the indole ring has been used to investigate stacking interactions of tryptophan with mercurinucleotides in mixed aggregates formed in frozen aqueous solutions as well as in oligopeptide-polynucleotide complexes. This effect is characterized at 77 K by a quenching of the tryptophan fluorescence, an enhancement of the phosphorescence emission and a drastic shortening of the phosphorescence lifetime. These phenomena result from an enhanced spin-orbit coupling due to a close contact between the mercury atom and the indole ring. Dissociation of the complexes leads to a recovery of the spectroscopic properties of the free tryptophan ring. The possible use of this spin-orbit probe to provide evidence for stacking interactions in protein-nucleic acid complexes is discussed.

Chemical Phenomena↗
PubMed1979

The role of tyrosine in the association of proteins and nucleic acids. Specific recognition of single-stranded nucleic acids by tyrosine-containing peptides.

Oligopeptides containing tyrosyl, lysyl, and alanyl residues bind to polynucleotides and nucleic acids as shown by proton magnetic resonance, fluorescence spectroscopy, and difference absorption spectroscopy. Proton magnetic resonance data indicate that stacking of tyrosyl residues with nucleic acid bases takes place only in single-stranded structures (such as poly(A) or denatured DNA). Stacking interactions lead to a quenching of tyrosine fluorescence. However, the tyrosyl fluorescence of the peptides is quenched in their complexes with both single-stranded and double-stranded nucleic acids. A comparison of the behavior of homologous peptides containing Tyr, methoxytyrosine, and Phe leads to the conclusion that hydrogen bonding of tyrosine with bases or phosphates is not involved in the investigated complexes. An energy transfer mechanism from tyrosine to nucleic acid bases is proposed to account for fluorescence quenching in oligopeptide complexes with double-stranded DNAs. Due to the specificity of its stacking interaction for single-stranded nucleic acid structures, tyrosine might be involved through such interactions in the selective recognition of single strands by proteins.

Alanine↗