This domain is found in the C-terminal region of free serine kinase (SerK) in the hyperthermophilic archaeon Thermococcus kodakarensis. SerK converts ADP and l-serine (Ser) into AMP and O-phospho-l-serine (Sep), which is a precursor of l-cysteine. The domain is not conserved in the ParB/Srx family. The differences between SerK and the other members of the ParB/Srx family is concentrated in the C-terminal region, which may include residues involved in the Sep binding [1].

1: Structural Study on the Reaction Mechanism of a Free Serine Kinase Involved in Cysteine Biosynthesis. Nagata R, Fujihashi M, Kawamura H, Sato T, Fujita T, Atomi H, Miki K; ACS Chem Biol. 2017;12:1514-1523. PMID:28358477