title: Tryptophan intercalation in G, C containing polynucleotides: Z to B conversion of poly [d(G-5M C)] in low salt induced by a tetra peptide.
abstract: Binding of a tetra peptide, lysyl tryptophenyl glycyl lysine O-ter butyl ester (KWGK) with duplex forms of G, C containing polynucleotides, Poly [d(G-C)], Poly [d(G-5M C)], Poly (dG), Poly (dC) and E.coli DNA were studied under low salt conditions using UV absorption, fluorescence, and circular dichroic (C.D) spectroscopy. On addition of the peptide (upto a P/N mole ratio of 0.5), the Poly [d(G-5M C)] under low salt (1 mM Na Cl) conditions, was converted from Z to B-form as shown by the inversion of C.D spectra. The two binding constants (K1 and K2) were determined from fluorescence spectroscopy of which K2 estimates the intercalation of the tryptophenyl side chain between the base pairs of DNA and K1 estimates the electrostatic interactions between the lysyl side chains and phosphate groups. The strength of intercalation is: Z-form of Poly [d(G-5M C)] >> B form of Poly [d(G-5M C)] >> E.Coli DNA > Poly (dG).Poly (dC). This means that peptide seems to have strong preference for Z compared to B-form and for alternating over non-alternating G, C Sequences. This suggests that tryptophan intercalation may act as a discriminating factor in recognizing Z and B-forms and may have a potential role in Protein-Nucleic acid interactions that are important for transcription.
authors.affiliation: Department of Biochemistry, All India Institute of Medical Sciences, New Delhi, India. raji@aiims.ernet.in
authors.forename: M R
authors.initials: MR
authors.lastname: Rajeswari
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D006207:Half-Life; D007364:Intercalating Agents / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D011119:Polynucleotides / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D012492:Salts; D013050:Spectrometry, Fluorescence; D013057:Spectrum Analysis / Q000379:methods; D014364:Tryptophan / Q000737:chemistry* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D007364:Intercalating Agents; D010455:Peptides; D011119:Polynucleotides; D012492:Salts; D014364:Tryptophan; D004247:DNA