Binding modes of V(= O)meso-tetrakis(N-methylpyridinium-4-yl)porphyrin to various synthetic DNAs studied by polarized spectroscopy

摘要

The interactions between water-soluble cationic oxovanadyl[meso-tetrakis(4-N-methylpyridiumyl)]porphyrin (VOTMPyP) and various synthetic polynucleotide including poly[d(A-T)(2)], poly[d(G-C)(2)], and poly[d(I-C)(2)] were studied using absorption, circular dichroism (CD), and linear dichroism (LD) spectroscopy. When VOTMPyP formed a complex with poly[d(A-T)(2)] and poly[d(I-C)(2)], a positive CD signal at low [VOTMPyP]/[DNA] ratios (R ratios) and strong excitonic CD signals at above R >= 0.15 were induced. The appearance of the CD spectra of the VOTMPyP-poly[d(G-C)(2)] complex were very different: a small negative CD at low R ratios and very small excitonic CD at high R ratios were observed. Considering the facts that the minor grooves of the former two polynucleotides resemble and the major groove of poly[d(I-C)(2)] is similar with that of poly[d(G-C)(2)], it is conclusive that VOTMPyP binds to the minor groove of all DNA at lower R ratios while they stack at the outside of DNA at higher R ratios. The binding geometry of VOTMPyP to all polynucleotides studied by LD seemed to be homogenous, irrespective of the R ratio. It has been found that VOTMPyP can have five- and six-fluxional coordination states. Comparing the absorption spectra of VOTMPyP complexed with poly[d(A-T)(2)] and poly[d(G-C)(2)], the distinctive absorptions of the five- and six-coordinated species were observed at lower R ratios which centered at 420-430 nm and 442 nm, respectively. While the six-coordinated VOTMPyP favored the poly[d(A-T)(2)], the five-coordinated species favored the poly[d(G-C)(2)] at the low R ratios. As the stacked species increased with an increasing R ratio, the six-coordinated species became the major bound species. These observations lead us to conclude that the guanine base' amino group plays a crucial role not only in determining the binding mode of VOTMPyP but also in the conversion of the six-coordinated species to the five-coordinated species. (C) 2005 Elsevier B.V. All rights reserved.