“…(HhH)2 domains are usually found as isolated domains, not in tandem arrangements (Shao & Grishin, 2000), which is another unusual characteristic of topoisomerase V. The topoisomerase domain has no sequence or structural similarities to other topoisomerases or any other proteins, making it a unique fold (Forterre, 2006;Taneja et al, 2006). The active site residues have been identified (Rajan, Osterman, Gast, & Mondragon, 2014), but their three dimensional arrangement suggest a different catalytic mechanism from other topoisomerases (Rajan et al, 2014). In the structures of the free protein, the topoisomerase domain active site is inaccessible as it is covered by the (HhH)2 domains (Rajan et al, 2016;Rajan et al, 2013;Rajan et al, 2010;Taneja et al, 2006).…”