PkwA, a WD-repeat protein, is expressed in spore-derived mycelium of Thermomonospora curvata and phosphorylation of its WD domain could act as a molecular switch

WD-repeat proteins are found in all eukaryotes and are implicated in a vari ety of regulatory functions as a result of protein-protein interactions. Pk wA from Thermomonospora curvata CCM3352 is a first potential example of a W D-repeat protein in a prokaryotic actinomycete. A mAb (3G2) was generated a gainst the carboxy terminus of PkwA and wa used to analyse the expression o f PkwA in T. curvata. PkwA was detected in exponential growth phase followi ng inoculation with spores, but could not be found at any stage of growth f ollowing inoculation with vegetative mycelium. PkwA and its WD domain were expressed in Escherichia coli as His-tag derivatives and purified on a Talo n metal affinity matrix. The WD domain was phosphorylated by Pkg2, a membra ne-spanning protein Ser/Thr kinase from 'Streptomyces granaticolor'. A memb rane fraction from an exponential, spore-derived culture of T. curvata was found to phosphorylate the WD domain specifically in the presence of Mn2+. These data confirm that PkwA is expressed in spore-derived exponential grow th phase of T. curvata and could play a role as a molecular switch in a sig nalling pathway.