WD40 domain of RqkA regulates its kinase activity and role in extraordinary radioresistance of D. radiodurans

RqkA, a DNA damage responsive serine/threonine kinase, is characterized for its role in DNA repair and cell division inD. radiodurans. It has a unique combination of a kinase domain at N-terminus and a WD40 type domain at C-terminus joined through a linker. WD40 domain is comprised of eight beta-propeller repeats held together via 'tryptophan-docking motifs' and forming a typical 'velcro' closure structure. RqkA mutants lacking the WD40 region (hereafter referred to as WD mutant) could not complement RqkA loss in gamma radiation resistance inD. radioduransand lacked gamma radiation-mediated activation of kinase activityin vivo. WD mutants failed to phosphorylate its cognate substrate (e.g. DrRecA) in surrogateE. colicells. Unlike wild-type enzyme, the kinase activity of its WD40 mutants was not stimulated by pyrroloquinoline quinine (PQQ) indicating the role of the WD motifs in PQQ interaction and stimulation of its kinase activity. Together, results highlighted the importance of the WD40 domain in the regulation of RqkA kinase signaling functionsin vivo,and thus, the role of WD40 domain in the regulation of any STPK is first time demonstrated in bacteria.