Studies on the cytoplasmic protein tyrosine kinase activity of the Antarctic psychrotrophic bacterium Pseudomonas syringae

The Antarctic psychrotrophic bacterium Pseudomonas syringae contains a 66-k Da cytoplasmic protein which was found to be phosphorylated on a tyrosine r esidue [Ray, M.K. et al. (1994) FEMS Microbiol. Lett. 122, pp. 49-54]. To i nvestigate the nature of the cytoplasmic protein tyrosine kinase and its ro le in the bacterial physiology, we carried out some biochemical studies of the enzyme in vitro in the presence of exogenous peptide substrates and exp ression studies in vivo at low and high temperature during various phases o f growth. The results suggest that the protein tyrosine kinase associated w ith the cytoplasmic fraction of the bacterium has certain similarities and dissimilarities with the known eukaryotic tyrosine kinases. The protein tyr osine kinase could phosphorylate exogenous substrate corresponding to the N -terminal peptide of p34(cdc2) kinase but could not do so on poly(Glu:Tyr). The enzyme could not be inhibited by genistein, staurosporine and dimethyl aminopurine, but could be inhibited by piceatannol which is a known compet itive inhibitor of the peptide binding site of mammalian protein tyrosine k inases. The enzyme activity in the cytoplasm is uniquely inhibited by sodiu m orthovanadate (IC50 = 20 mu M) which is a known protein tyrosine phosphat ase inhibitor. The expression studies show that the enzyme is produced more at a higher temperature (22 degrees C) of growth than at lower temperature (4 degrees C) and during the stationary phase of growth of P. syringae. (C ) 1999 Federation of European Microbiological Societies. Published by Elsev ier Science B.V. All rights reserved.