Ca2+ improves organization of single-stranded DNA bases in human Rad51 filament, explaining stimulatory effect on gene recombination
Journal article, 2012

Human RAD51 protein (HsRad51) catalyses the DNA strand exchange reaction for homologous recombination. To clarify the molecular mechanism of the reaction in vitro being more effective in the presence of Ca2+ than of Mg2+, we have investigated the effect of these ions on the structure of HsRad51 filament complexes with single- and double-stranded DNA, the reaction intermediates. Flow linear dichroism spectroscopy shows that the two ionic conditions induce significantly different structures in the HsRad51/single-stranded DNA complex, while the HsRad51/double-stranded DNA complex does not demonstrate this ionic dependence. In the HsRad51/single-stranded DNA filament, the primary intermediate of the strand exchange reaction, ATP/Ca2+ induces an ordered conformation of DNA, with preferentially perpendicular orientation of nucleobases relative to the filament axis, while the presence of ATP/Mg2+, ADP/Mg2+ or ADP/Ca2+ does not. A high strand exchange activity is observed for the filament formed with ATP/Ca2+, whereas the other filaments exhibit lower activity. Molecular modelling suggests that the structural variation is caused by the divalent cation interfering with the L2 loop close to the DNA-binding site. It is proposed that the larger Ca2+ stabilizes the loop conformation and thereby the protein–DNA interaction. A tight binding of DNA, with bases perpendicularly oriented, could facilitate strand exchange.


Louise Fornander

Chalmers, Chemical and Biological Engineering, Physical Chemistry

Karolin Frykholm

University of Gothenburg

Anna Reymer

Chalmers, Chemical and Biological Engineering, Physical Chemistry

A. Renodon-Corniere

Nantes University

Masayuki Takahashi

Nantes University

Bengt Nordén

Chalmers, Chemical and Biological Engineering, Physical Chemistry

Nucleic Acids Research

0305-1048 (ISSN) 1362-4962 (eISSN)

Vol. 40 11 4904-4913

Supramolecular Motive Power (SUMO)

European Commission (EC) (EC/FP7/227700), 2009-01-01 -- 2014-12-31.

Areas of Advance

Nanoscience and Nanotechnology (SO 2010-2017, EI 2018-)


Life Science Engineering (2010-2018)

Subject Categories

Physical Chemistry

Biochemistry and Molecular Biology


Basic sciences



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