Conformational dynamism in d-(GAATTCCGTTATT) containing the complementary Myb responsive element d-CCGTTA: NMR and MD...

Conformational features of the DNA segment d-(GAATTCCGTTATT) containing the complementary Myb responsive element CCGTTA has been studied by NMR and molecular dynamics calculations with a view to see the role of 3D structure in specific DNA recognition. From the low field imino proton NMR spectra, the DNA sequence is seen to exist as a duplex with pyrimidine mismatches in the centre. The 2D NMR spectra however show that teh molecule exhibits substantial dynamism even at 1 degree C. Several extra cross peaks, more than the expected number, are seen in particular regions in all the spectra. These observations indicate that the duplex undergoes slow transitions between base-paired and unbase-paired states due to mismatches in the centre. Hence, to characterise those transitions a restrained verlet dynamics has been performed for 50ps using X-PLOR force field. Structural intermediates at regular intervals have been analysed, and we see that the dynamism in the molecule results in substantial fluctuations in the different torsion angles. The mismatch sites are seen to exhibit the highest degree of fluctuations, with the bases stacking in and looping out of the duplex. The sugar geometry is seen to be fairly steady around the S domain for most of the residues.