Solution Small Angle X-ray Scattering (SAXS) Studies of RecQ from Deinococcus radiodurans and Its Complexes with Junction DNA Substrates

RecQ helicases, essential enzymes for maintaining genome integrity, possess the capability to participate in a wide variety of DNA metabolisms. They can initiate the homologous recombination repair pathway by unwinding damaged dsDNA and suppress hyper-recombination by promoting Holliday junction (HJ) migration. To learn how DrRecQ participates in the homologous recombination repair pathway, solution structures of Deinococcus radiodurans RecQ (DrRecQ) and its complexes with DNA substrates were investigated by small angle x-ray scattering. We found that the catalytic core and the most N-terminal HRDC (helicase and RNase D C-terminal) domain (HRDC1) undergo a conformational change to a compact state upon binding to a junction DNA. Furthermore, models of DrRecQ in complexes with two kinds of junction DNA (fork junction and HJ) were built based on the small angle x-ray scattering data, and together with the EMSA results, possible binding sites were proposed. It is demonstrated that two DrRecQ molecules bind to the opposite arms of HJ. This architecture is similar to the RuvAB complex and is hypothesized to be highly conserved in the other HJ migration proteins. This work provides us new clues to understand the roles DrRecQ plays in the RecFOR pathway.