title: Effect of nucleic acid binding on the triplet state properties of tetrapeptides containing tryptophan and 6-methyltryptophan: a study by phosphorescence and ODMR spectroscopy.
abstract: Complexes of four peptides [KWGK, KGWK, K(6MeW)GK, KG(6MeW)K] with the nucleic acids [poly(A), poly(C), poly(U), poly(I), and rG(8)] have been investigated by phosphorescence and optically detected magnetic resonance (ODMR) spectroscopy. The intrinsic spectroscopic probes used in these studies are tryptophan (W) and 6-methyltryptophan (6MeW). Binding to the nucleic acids results in a red-shift of the phosphorescence 0,0-band (delta E(0,0)) of the aromatic residue as well as a reduction of its zero-field splitting parameter (delta D). Results are compared with earlier studies of the HIV-1 nucleocapsid protein, NCp7, that contains a single tryptophan residue (Trp37) within a retroviral zinc finger sequence. Binding of poly(A) or poly(U) to the tetrapeptides induces larger delta E(0,0) and delta D than when bound to NCp7, indicating stronger stacking interactions. Poly(I), on the other hand, produces larger shifts in Trp37 of NCp7. Binding of rG(8) produces sequence-dependent effects in the peptides. When bound to NCp7, but in contrast with tetrapeptide binding, nucleic acids produce large changes in triplet state kinetics consistent with enhanced spin-orbit coupling. These results are discussed in terms of three limiting types of tryptophan-base interaction: intercalation, aromatic stacking, and edge-on interaction. These should have differing effects on the properties of the triplet state.
authors.affiliation: Department of Chemistry, University of California, Davis, California 95616, USA.
authors.forename: A
authors.initials: A
authors.lastname: Misra
authors.forename: A
authors.initials: A
authors.lastname: Ozarowski
authors.forename: J R
authors.initials: JR
authors.lastname: Casas-Finet
authors.forename: A H
authors.initials: AH
authors.lastname: Maki
mesh_terms: D001665:Binding Sites; D004247:DNA / Q000737:chemistry; D007700:Kinetics; D008163:Luminescent Measurements; D008872:Microwaves; D019906:Nuclear Magnetic Resonance, Biomolecular; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D020135:Peptide Nucleic Acids / Q000737:chemistry*; D014364:Tryptophan / Q000031:analogs & derivatives* / Q000737:chemistry*
chemical_list: D009842:Oligopeptides; D020135:Peptide Nucleic Acids; D014364:Tryptophan; D004247:DNA