CHARACTERIZATION OF A PHOSPHOPROTEIN PHOSPHATASE FOR THE PHOSPHORYLATED FORM OF NUCLEOSIDE-DIPHOSPHATE KINASE FROM PSEUDOMONAS-AERUGINOSA

Nucleoside-diphosphate kinase (ATP:nucleoside-diphosphate phosphotrans ferase, EC 2.7.4.6; NDP kinase) is an important enzyme for the mainten ance of the correct cellular levels of nucleoside triphosphates (NTPs) and their deoxy derivatives (dNTPs) and is involved in the regulation of cellular development, The enzyme is under the dual control of algR 2 and algH in Pseudomonas aeruginosa. We report here the purification and characterization of a protein that dephosphorylates the phosphoryl ated intermediate form of the P. aeruginosa NDP kinase (Ndk), Dephosph orylation of Ndk phosphate leads to loss of its enzymatic activity, Th e 10.1-kDa polypeptide shows 77% homology at the N terminus with the S po0E phosphatase, identified as a negative regulator of sporulation in Bacillus subtilis and 66% with the human Bax protein, identified as a n effector of programmed cell death, The phosphatase termed Npp showed varied specificity toward phosphorylated Ndks from different sources including human erythrocyte Ndk phosphate. Its activity toward other h istidine phosphates such as CheA or the alpha-subunit of succinyl-CoA synthetase or phosphoesters such as p-nitrophenyl phosphate was quite limited, Npp was stable at room temperature up to 2 h and required Mg2 + for activity, The presence of a phosphatase capable of dephosphoryla ting the phosphorylated form of P. aeruginosa Ndk represents an intere sting and efficient mode of post-translational modification of an enzy me crucial to cellular development.