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Effects of sibiromicyn, distamicyn A and its analogs on binding to DNA and to poly(dA).poly(dT) are reported for a 23-amino acid synthetic zinc-binding peptide, a part of the DNA-binding domain of the transcriptional activator GAL-4. Circular dichroism and fluorometry have shown that the synthetic peptide and two distamicyn A analogs compete for binding sites on DNA and on poly(dA).poly(dT). Antibiotic sibiromycin which forms a covalent bond with a guanine 2-amino group in the minor DNA groove can displace the peptide from a 19 bp self-complementary oligonucleotide serving as a specific target site for Gal-4 protein. The peptide is shown to bind to a glucosylated phage T2 DNA, but its affinity to T2 DNA is weaker than to calf thymus DNA under the same conditions. A method to estimate binding constant and size of the binding site for the synthetic peptide and poly(dA).poly(dT) is proposed based on the binding isotherms of distamycin analogs in the absence and in the presence of the peptide. Using isotherms of binding to poly(dA).poly(dT) for two distamycin analogs with binding constants differing 60-fold, the binding constant of the peptide in the presence of 0.1 M NaCl is estimated as 1.4.10(7)-1.8.10(7) M-1.

De novo design and synthesis by a solid phase technique of linear and cyclic 26-residues peptides are reported. The peptides use beta-strand-turn-beta -strand motif for sequence recognition on DNA. Amino acid sequences in the two peptides are identical, but the structure of the cyclic peptide is constrained by S-S bridge between two cysteine residues. A 28-residue peptide containing at the N-terminus a copper-chelating peptide Gly-Gly-His is also synthesized which can be used as a potential DNA-cleaving reagent. Binding of these peptides to various natural and synthetic DNAs and DNA fragment with a known base pair sequence has been studied by CD spectroscopy, fluorescence methods and DNAse I footprinting technique. By means of CD spectroscopy it is shown that 26-residue linear and cyclic peptides are partially in disordered and beta-conformations in aqueous solution in absence and in presence of 20% trifluoroethanol (TFE), but assume partially an alpha-helix conformation in the presence of 50% TFE. It is shown that linear and cyclic peptides bind to DNA. The binding approaches saturation level when one peptide molecule is bound approximately per three or four DNA base pairs. We found that antibiotic distamycin A, binding in the minor DNA groove, competes effectively with the 26-residue linear and cyclic peptides for binding to poly(dA).poly (dT). According to the CD spectroscopy data the linear and cyclic peptides undergo conformation changes upon binding to DNA, whereas the DNA structure is not markedly altered. Difference CD spectra obtained by subtracting the spectrum of the free DNA from the spectrum of the peptide-DNA mixture differ from the spectrum of the free peptide. The shapes of difference CD spectra are consistent with a conformation transition from a disordered conformation into a beta-like conformation upon binding of peptide to DNA. DNAase I footprinting diagrams show that there is a specific protection by linear and cyclic peptides of the nucleotide sequences on two ends of operators OR1, OR2 and OR3 and pseudooperators within the cro gene of 434 phage.

Synthesis and DNA-binding activity of the synthetic 26-residue peptide, containing in two copies a part of the DNA-binding domain of the transcription activator v-Jun, are reported. Using CD spectroscopy, it has been shown that the peptide exists in a random coil conformation in aqueous solution, but assumes partially an alpha-helical conformation in the presence of 20% trifluoroethanol. The percentage of alpha-helix is increased in the presence of 40% trifluoroethanol up to approximately 80%. It has been shown that the peptide forms two types of complexes with DNA. The first type of complexes saturates when one peptide molecule occupies six base pairs. At further increase of molar peptide to DNA ratio the binding became a cooperative process. The binding approaches saturation when one peptide molecule is bound approximately to four DNA base pairs. The binding constant of the monomer peptide complex with DNA has been estimated to be approximately 1.10(5) M-1 in the presence of 0.2 M NaCl. The peptide binds more strongly to poly(dG).poly(dC) and poly(dA).poly(dT) than to poly[d(GC)].poly[d(GC)]. We found that the DNA minor groove-binding antibiotic distamycin A competes effectively with the peptide for binding to poly(dA).poly(dT).

Synthesis and DNA-binding activities of the two synthetic 26-residue peptides, containing in two copies a part of the DNA-binding region of the transcription activator v-Jun, are reported. Aminoacid sequences of the two peptides are identical, but in one of them the structure of the DNA-binding region is stabilized by S-S-bond between the two cysteine residues. Using CD spectroscopy, it is shown that the two peptides exist in a random coil conformation in aqueous solution, but assume partially an alpha-helical conformation in the presence of 20% trifluoroethanol. The percentage of alpha-helix is increased in the presence of 40% trifluoroethanol up to approximately 65% and 40% in the absence and presence of S-S-bond between the two cysteine residues, respectively. Evidently, formation of S-S-bond prevents a coil to alpha-helix transition in one of the two DNA-binding regions of the peptide, whereas the formation of alpha-helix in another DNA-binding region is allowed. It is shown that the two peptides bind to DNA. We found that the DNA minor groove-binding antibiotic distamycin A competes with the two peptides for binding to poly(dA).poly(dT). The binding of the two peptides to DNA is accompanied by conformational transitions in the peptide molecules, whereas the structure of DNA does not undergo a marked change. The difference CD spectrum obtained by subtracting the spectrum of DNA from the spectrum of a peptide-DNA mixture differs from the CD spectrum of the free peptide. The shapes of the difference CD spectra are consistent with alpha-beta and coil-beta transitions induced upon binding of the two peptides to DNA. DNase I footprinting diagrams show that peptides mediated cleavage protection of DNA takes place at regions containing 5'-TGA-3' and 5'-TGC-3' nucleotide sequences.

Synthesis, DNA- and zinc ion-binding activities of the synthetic 23-residue peptide, forming a part of the DNA-binding domain of yeast transcription activator GAL-4, are reported. In presence of zinc ions considerable changes in the shapes of the fluorescence and CD spectra of the peptide are observed. It is shown that the peptide forms complexes with zinc ions containing one metal ion per peptide molecule with association constants on the order of (1-2) x 10(6) M-1. Using gel filtration on a TSK-gel column we have shown that in aqueous solution at concentrations of 10(-4)-10(-6) M the peptide exists predominantly in the dimeric form. Dimerization constants were found to be 5 x 10(6) M-1 and 1.7 x 10(7) M-1 in the absence and in the presence of zinc ions, respectively. It is shown that the peptide binds to DNA. The binding approaches saturation when one peptide molecule is bound approximately to five base pairs of DNA. The shapes of the titration curves obtained from binding of the peptide to DNA show that the peptide can bind to DNA both in the monomeric and self-associated forms (dimer or tetramer). Increasing DNA concentration and decreasing the peptide/DNA molar ratio lead to a shift in the equilibria between self-associated peptide species and monomers toward the formation of monomer peptide complexes.

Design, synthesis and DNA binding activity of a nonlinear 102 residue peptide are reported. The peptide contains four sequence-specific DNA binding domains of 434 Cro protein. These four domains were linked covalently to a symmetrical carboxyterminal crosslinker that contains four arms each ending with an aliphatic aminogroup. From CD studies we have found that in aqueous buffer in the presence of 20% trifluoroethanol the peptide residues assume alpha helical, beta-sheet and random coiled conformations with an alpha helical content of about 16% at room temperature. The alpha helicity is increased up to 40% in the presence of 40% trifluoroethanol. Upon complex formation between the peptide and DNA a change in the peptide conformation takes place which is consistent with an alpha-beta transition in the DNA binding, helix-turn-helix motif of 434 Cro repressor. Evidently residues present in helices alpha(2) and alpha(3) form a beta hairpin which is inserted in the minor DNA groove. The latter inference is supported by our observations that the peptide can displace minor groove binding antibiotic distamycin A from a complex with poly(dA).poly(dT). As revealed from DNase protection studies the peptide exhibits preferences for binding to operator and pseudooperator sites recognized by 434 Cro repressor. It binds strongly to operator sites OR1, OR2 and OR3 and exhibits a greater affinity for pseudooperator site Op1. From analysis of nucleotide sequences in the strong affinity binding sites for the peptide on DNA a conclusion is drawn that it binds to pseudosymmetrical nucleotide sequences 5'-ACAA(W)nCTGT-3', where W is an arbitrary nucleotide. n is equal to six or seven. In the strongest affinity binding site for the peptide on DNA (Op1) motif 5'-ACAA-3' is replaced by sequence 5'-ACCA-3'. A difference in binding specificity shown by the peptide and 434 Cro protein could be attributed to a flexibility of the connecting chains between DNA-binding domains in the peptide molecule as well as to a replacement of Thr - Ala in the alpha 2 helix. Removal of two residues from the N-terminal end of helix alpha 2 in each of the four DNA binding domains of 434 Cro present in the peptide leads to a loss of binding specificity, although the modified peptide binds to DNA unspecifically.

In the present communication, design, synthesis and DNA binding activities of the following two peptides are reported: Dns-Gly-Ala-Gln-Lys-Leu-Ala-Cly-Lys-Val-Gly-Thr-Lys-Val-Lys-Val-Gl y-Thr-Lys-Thr - Val-OH (I) and [(H-Ala-Lys-Leu-Ala-Thr-Lys-Ala-Gly-Val-Lys-Gln-Gln-Ser-Ile-Gln-Leu-Ile- Thr- Ala-Aca-Lys-Aca)2Lys-Aca]2Lys-Val-OH (II), where Aca = NH(CH2)5CO--; Dns is a residue of 5-dimethylaminonaphtalene-1-sulfonic acid. Peptide I contains a large fraction (ca.30%) of valyl and threonyl residues, which possess a high potential for beta structure formation. Peptide II contains four repeats of the amino acid sequence present in the presumed DNA binding helix-turn-helix unit of 434 Cro repressor. These four domains are linked in such a way that two domains can interact with two halves a 14 base pair long operator site on DNA. From CD studies we have found that peptide I is in a random coil conformation in the aqueous solution in the presence of 20% trifluoroethanol. By contrast, amino acid residues of peptide II assume alpha helical, beta and random coiled conformations under the same conditions. A change in the secondary structure of the two peptides upon binding to DNA is observed. The difference CD spectra obtained by subtracting the spectra of free DNA from the spectra of peptide I--DNA complexes gives rise to a beta-like pattern. The difference CD spectra obtained for complexes of peptide II with various natural and synthetic DNAs suggest that alpha-beta-transition takes place in the presumed helix-turn-helix repeat units of peptide II upon binding to DNA. Peptide I binds more strongly to poly(dG).poly(dC) than to poly(dA).poly(dT) and poly[d(GC)].poly[d(GC)]. The binding takes place in the minor DNA groove because minor groove binding antibiotic sibiromycin can displace peptide I from a complex with poly(dG).poly(dC). Analysis of footprinting diagramms shows that peptide I specifically protects phosphodiester bonds within operator sites OR1 and OR2 of phage lambda from nuclease cleavage. By contrast, peptide II does not react specifically with operators OR1, OR2 and OR3 of phage 434 although it forms very tight complexes with DNA which are stable in the presence of 1M NH4F.