title: Role of structure-proteins in the porphyrin-DNA interaction.
abstract: We studied the complexation of meso-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP) with HeLa nucleosomes and compared it to our earlier results on T7 phage nucleoprotein complex (NP) and isolated DNA. To identify binding modes and relative concentrations of the bound TMPyP forms, the porphyrin absorption spectra were analyzed at various base pair/porphyrin ratios. Spectral decomposition and circular dichroism measurements proved that the two main binding modes of TMPyP, i.e., external binding and intercalation occur also in the nucleosomes. The DNA superstructure maintained by the proteins decreases its accessibility for TMPyP similarly in both nucleoproteins. A difference is observed between the partitioning of the two binding modes: in the case of nucleosome the ratio of intercalation to groove-binding is changed from 60/40 to 40/60 as determined for T7 NP and for isolated DNA-s. Using UV and CD melting studies, we revealed that TMPyP destabilizes the DNA-protein interaction in the nucleosomes but not in the T7 phage. Lastly, photoinduced reaction of bound TMPyP caused alterations in DNA structures and DNA-protein interactions within both nucleoprotein complexes; the nucleosomes were found to be more sensitive to the photoreaction.
authors: Institute of Biophysics and Radiation Biology, Semmelweis University, H-1444 Budapest, P.O. Box 263, Hungary. gabriella.csik@eok.sote.hu
authors: Gabriella
authors: G
authors: Csík
authors: Marianna
authors: M
authors: Egyeki
authors: Levente
authors: L
authors: Herényi
authors: Zsuzsa
authors: Z
authors: Majer
authors: Katalin
authors: K
authors: Tóth
mesh_terms: D045744:Cell Line, Tumor; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007364:Intercalating Agents / Q000737:chemistry / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D009698:Nucleoproteins / Q000378:metabolism* / Q000502:physiology; D009707:Nucleosomes / Q000378:metabolism / Q000502:physiology; D011166:Porphyrins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D014466:Ultraviolet Rays
chemical_list: D007364:Intercalating Agents; D009698:Nucleoproteins; D009707:Nucleosomes; D011166:Porphyrins; C021096:tetra(4-N-methylpyridyl)porphine; D004247:DNA