Purification and preliminary analysis of the nuclease and capping domain of the DNA repair exonuclease SbcD from the Grampositive bacteria Staphylococcus aureus

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The SbcCD complex is the bacterial Mre11-Rad50 homolog, and cleaves blocked DNA ends and hairpins by an ATPdependent endo- and exonuclease activities to repair DNA. The SbcC component consists of an ATP-binding cassettetype nucleotide-binding domain and a flanking coiled-coil insertion containing a dimerization motif. The SbcD component consists of a nuclease and capping domain, a linker region, and a helix-loop-helix (HLH) domain. The structural studies have been in Gram-negative bacteria. It remains to be elucidated the action mechanism at the molecular level, especially in Gram-positive bacteria. Here, we studied the nuclease and capping domain of SbcD from the Gram-positive bacteria Staphylococcus aureus. The protein was overexpressed and purified, and its crystals suitable for the structural study were obtained. We collected X-ray diffraction dataset at a resolution of 3.5 Å. The crystals belong to space group P2₁2₁2₁, with unit cell parameters a = 72.6, b = 88.9, and c = 115.8 Å. The molecular replacement trials were failed to determine the structure, and thus we are now growing the Se-Met substituted crystals to solve the crystal structure. This structure will give molecular insights into the DNA repair process mediated by the SbcCD complex, in the Gram-positive bacteria.