Putative XerD in Streptococcus pneumonia and similar proteins, C-terminal catalytic domain
This family includes a putative XerD recombinase in Streptococcus pneumonia and similar tyrosine recombinases. However, the members of this family contain unusual active site motifs from the XerD from Escherichia coli. E. coli XerD and homologous enzymes show four conserved amino acids R-H-R-H that are spaced along the C-terminal domain. The putative S. pneumoniae XerD contains three unique replacements at the conserved positions resulting in L-Q-R-L. Severe growth defects in a loss-of-function xerD mutant demonstrate an important in vivo function of the S. pneumoniae XerD protein. This family belongs to the superfamily of DNA breaking-rejoining enzymes, which share the same fold in their catalytic domain and the overall reaction mechanism. The catalytic domain contains six conserved active site residues. Their overall reaction mechanism involves cleavage of a single strand of a DNA duplex by nucleophilic attack of a conserved tyrosine to give a 3' phosphotyrosyl protein-DNA adduct. In the second rejoining step, a terminal 5' hydroxyl attacks the covalent adduct to release the enzyme and generate duplex DNA.
Jiyao W et al.(2023). "The conserved domain database in 2023.",