Structure of the human DNA-repair protein RAD52 containing surface mutations

The Rad52 protein is a eukaryotic single-strand DNA-annealing protein that is involved in the homologous recombinational repair of DNA double-strand breaks. The isolated N-terminal half of the human RAD52 protein (RAD52^1-212) forms an undecameric ring structure with a surface that is mostly positively charged. In the present study, it was found that RAD52^1-212 containing alanine mutations of the charged surface residues (Lys102, Lys133 and Glu202) is highly amenable to crystallization. The structure of the mutant RAD52^1-212 was solved at 2.4 Å resolution. The structure revealed an association between the symmetry-related RAD52^1-212 rings, in which a partially unfolded, C-terminal region of RAD52 extended into the DNA-binding groove of the neighbouring ring in the crystal. The alanine mutations probably reduced the surface entropy of the RAD52^1-212 ring and stabilized the ring-ring association observed in the crystal.