TOPRIM_TopoIA: topoisomerase-primase (TOPRIM) nucleotidyl transferase/hydrolase domain of the type found in the type IA family of DNA topoisomerases (TopoIA). This subgroup contains proteins similar to the Type I DNA topoisomerases: E. coli topisomerases I and III, eukaryotic topoisomerase III and, ATP-dependent reverse gyrase found in archaea and thermophilic bacteria. Type IA DNA topoisomerases remove (relax) negative supercoils in the DNA. These enzymes cleave one strand of the DNA duplex, covalently link to the 5' phosphoryl end of the DNA break and allow the other strand of the duplex to pass through the gap. Reverse gyrase is also able to insert positive supercoils in the presence of ATP and negative supercoils in the presence of AMPPNP. The TOPRIM domain has two conserved motifs, one of which centers at a conserved glutamate and the other one at two conserved aspartates (DxD). For topoisomerases the conserved glutamate is believed to act as a general base in strand joining and, as a general acid in strand cleavage. The DXD motif may co-ordinate Mg2+, a cofactor required for full catalytic function.
Comment:involved in both strand cleavage and rejoining
Comment:reaction is Mg2+ dependent
Structure:1I7D_A; Escherichia coli topoisomerase III with bound ssDNA, contacts at 3.5A - View structure with Cn3D
Comment:catalytic mechanism of ssDNA cleavage in 1I7D_A: active site tyrosine forms a covalent linkage with the 5' phosphate of the scissile bond and conserved glutamate of TOPRIM domain donates a proton to the leaving 3' oxygen of the scissile bond
Structure:1CY4_A, E.coli Dna Topoisomerase I, bound with thymidine-5'-phosphate, contacts at 3.5A - View structure with Cn3D