The Interaction of Zn Metalloporphyrin with Different Forms of tRNA

Abstract

The interaction of meso-tetra-(4N-oxyethylpyridyl)porphyrin (TOEPyP4) and its Zn(II), Cu(II), -metallocomplexes with tRNA at low ionic strength we have investigated earlier [1]. In this work we have studied the binding of ZnTOEPyP4 with tRNA which has 2 forms: hairpin structure and spatial reversed “L” structure. The interaction of tRNA from E.Coli with ZnTOEPyP4 is studied by UV/Vis Spectrophotometry and Circular Dichroism methods.The measurements were performed in 0.1 BPSE and 1BPSE buffers (1 BPSE = 6 mM Na2HPO4+ 2 mM NaH2PO4 +185 mM NaCl + 1 mM Na2EDTA), correspondingly μ = 0.02M and μ = 0.2M, pH 6.57. (tRNA has hairpin form at μ = 0.02M and reversed “L” structure, when μ = 0.2M.)From the spectrophotometric titration datas the Scatchard binding isotherms for porphyrin-tRNA complexes are built and binding parameters are calculated (the number of binding sites per molecule of tRNA, and the binding constant).In both cases of tRNA's structure the induced CD spectra (at 400-470 nm) for complex of ZnTOEPyP4 with tRNA are very unusual. The induced CD spectra of complex change a sign and continue to grow (remaining negative) starting from a certain relative concentration. In case of tRNA's reversed “L” structure the intensity of ICD spectra for the same relative concentration of porphyrin is twice bigger than in case of hairpin structure. It is possible that at high relative concentration of porphyrins the liquid crystal form may exist in the solution.The binding constants with tRNA in case of hairpin form are an order of magnitude greater than in case of reversed “L” structure. It means that this porphyrin interacts stronger with tRNA when it has hairpin form.Reference1. Y. Dalyan, I. Vardanyan, A. Chavushyan,G. Balayan. J of Biomol Structure & Dynamics 28, 123-131 (2010).