title: ADP stabilizes the human Rad51-single stranded DNA complex and promotes its DNA annealing activity.
abstract: BACKGROUND
  Human Rad51 protein (HsRad51) is a homologue of Escherichia coli RecA protein, and involved in homologous recombination. These eukaryotic and bacterial proteins catalyse strand exchange between two homologous DNA molecules, each forming a complex with single-stranded DNA (ssDNA) and ATP as the initial step. Both proteins hydrolyse ATP; however, the role of ATP hydrolysis appears to vary between the two proteins.
  
  
  RESULTS
  Measurements using the fluorescence ssDNA analogue, poly(1,N6-etheno-deoxyadenosine), indicate that ATP affects the HsRad51-ssDNA complex, promoting two conformational states: one transient, rather rigid transition state and a final more flexible state. While ADP lowers the affinity of RecA protein to ssDNA, it is found to rather stabilize the HsRad51-ssDNA complex. ADP does not activate the strand exchange by HsRad51 but instead stimulates annealing between complementary ssDNAs.
  
  
  CONCLUSIONS
  The hydrolysis of ATP promotes a transition of the HsRad51-ssDNA complex from a stiff state to less stiff state. The first state may be important for the strand separation of dsDNA in the initial step of strand exchange, while the second state may be important for annealing in the next step. However, hydrolysis does not dissociate HsRad51 from DNA as a component step of its recycling.
authors.affiliation: Department of Physical Chemistry, Chalmers University of Technology, SE 412 96, Gothenburg, Sweden.
authors.forename: Hye-Kyung
authors.initials: HK
authors.lastname: Kim
authors.forename: Katsumi
authors.initials: K
authors.lastname: Morimatsu
authors.forename: Bengt
authors.initials: B
authors.lastname: Nordén
authors.forename: Malin
authors.initials: M
authors.lastname: Ardhammar
authors.forename: Masayuki
authors.initials: M
authors.lastname: Takahashi
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000235:genetics*; D006801:Humans; D051135:Rad51 Recombinase; D011995:Recombination, Genetic / Q000502:physiology*
chemical_list: D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; C495153:RAD51 protein, human; D051135:Rad51 Recombinase