Conformations and dynamics of the phosphodiester backbone of a DNA fragment that bears a strong topoisomerase II cleavage site.
The dynamics of the DNA phosphodiester backbone conformations have been studied for a strong topoisomerase II cleavage site (site 22) using molecular dynamics simulations in explicit water and in the presence of sodium ions. We investigated the backbone motions and more particularly the BI/BII transitions involving the epsilon and zeta angles. The consensus cleavage site is adjacent to the phosphate which shows the most important phosphodiester backbone flexibility in the sequence. We infer that these latter properties could be responsible for the preferential cleavage at this site possibly through the perturbation of the cleavage/ligation activities of the topoisomerase II. More generally, the steps pur-pur and pyr-pur are those presenting the highest BII contents. Relations are observed between the backbone phosphodiester BI/BII transitions and the flexibility of the deoxyribose sugar and the helical parameters such as roll. The roll is sequence dependent when the related phosphate is in the BI form, whereas this appears not to be true when it is in the BII form. The BI/BII transitions are associated with water migration, and new relations are observed with counterions. Indeed, it is observed that a strong coupling exists between the BII form and the presence of sodium ions near the adjacent sugar deoxyribose. The presence of sodium ions in the O4' surroundings or their binding could assist the BI to BII transition by furnishing energy. The implications of these new findings and, namely, their importance in the context of the sequence-dependent behavior of BI/BII transitions will be investigated in future studies.
René
Brigitte
B
UMR 8113 CNRS, Laboratoire de Biotechnologies et Pharmacologie Génétique Appliquée (Ecole Normale Supérieure de Cachan), Institut Gustave Roussy, 39 rue Camille Desmoulins, 94805 Villejuif Cedex, France.
Masliah
Grégoire
G
Antri
Saïd El
SE
Fermandjian
Serge
S
Mauffret
Olivier
O
D001483:Base Sequence; D004247:DNA / Q000737:chemistry*; D004250:DNA Topoisomerases, Type II / Q000737:chemistry / Q000378:metabolism*; D004952:Esters / Q000737:chemistry; D009690:Nucleic Acid Conformation
D004952:Esters; D004247:DNA; D004250:DNA Topoisomerases, Type II