This is the C-terminal domain found in archaeal type 2 DNA topoisomerase 6 subunit B (EC:5.99.1.3). This region is a small helix-two turns-helix (H2TH) domain inserted between the GHKL and transducer domains which adopts an immunoglobulin-like fold. Mutation analysis of this C-terminal domain showed that the overall activity of the mutant mesophilic methanogen M. mazei Top6B (MmT6) is modestly reduced but its relative activity on different substrates is not affected. Due to the similarity of the B subunit's CTD to known protein- and carbohydrate-binding modules, it has been suggested that it could regulate topo VI spatially, perhaps by localizing the enzyme to a specific subcellular region or functional partner [1].

1: Holoenzyme assembly and ATP-mediated conformational dynamics of topoisomerase VI. Corbett KD, Benedetti P, Berger JM; Nat Struct Mol Biol. 2007;14:611-619. PMID:17603498