Structural Features Of The DNA G-Quadruplexes Using Electrospry Lonization Mass Spectrometry(ESI-MS)

Electrospray ionization mass spectrometry (ESI-MS) with soft ionization technique is superior for the analysis of non-covalent interactions and stoichiometries of molecular complexes, because the noncovalent molecular interactions which formed in solution can survive in the gas phase in the process of the molecular ions transferred from solution to the gas phase. In addition, ESI-MS has advantages in speed and sensitivity for sample analysis, therefore, it has been used for determination of structure features of proteins and nucleic acid and has provided important structural information that other analytical techniques can not do. In this work, we using ESI-MS combined with circular dichroism (CD) spectroscopy studied the structures features of guanine-rich DNA oligonucleotides, in terms of stoichiometry and strand orientation, in following two aspects:1. Structure features of Anti-HIV DNA G-Quadruplexes formed by T30175, T30923 and their derivatives in ammonium acetate solution. Previous studies showed that the oligonucleotides T30175 and T30923 could form into G-Quadruplex structure which was similar to the structure of 93del, and therefore showed anti-HIV integrase activities at nanomole level. The other sequences which are derivatives of the T30175 or T30923 show different thermodynamic stability and anti-HIV integrase activity compared with them. Our ESI-MS results demonstrated that all of those oligonucleotides can form into DNA G-Quadruplex structure except the sequence of T30677, and formed parallel bimolecular G-Quadruplexes which were similar to that of the 93del in high concentrated ammonium acetate solution. The structural information obtained in this study is compared with IC50 or EC50 reported, the correlations between DNA G-Quadruplex structure and their anti-HIV activities are established.2. G-rich DNA sequences that form interlocked bimolecular G-Quadruplexes. Sixteen G-rich oligonucleotides in a certain concentration of ammonium acetate solution were study using ESI-MS. The ESI-MS result were compared with that of 93del, which be reported to form interlocked bimolecular DNA G-Quadruplex. The results showed that the sequences containing four repeating Gs at 5'end could form interlocked bimolecular DNA G-Quadruplexes, and one more thymine or guanine at the loop did not affect the form of interlocked bimolecular DNA G-Quadruplex structures. The present work provides valuable information for predicting the form of interlocked bimolecular DNA G-Quadruplex based on DNA sequences only.