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

Abstract

The Antarctic psychrotrophic bacterium Pseudomonas syringae contains a 66-kDa cytoplasmic protein which was found to be phosphorylated on a tyrosine residue [Ray, M.K. et al. (1994) FEMS Microbiol. Lett. 122, pp. 49^54]. To investigate the nature of the cytoplasmic protein tyrosine kinase and its role in the bacterial physiology, we carried out some biochemical studies of the enzyme in vitro in the presence of exogenous peptide substrates and expression studies in vivo at low and high temperature during various phases of growth. The results suggest that the protein tyrosine kinase associated with the cytoplasmic fraction of the bacterium has certain similarities and dissimilarities with the known eukaryotic tyrosine kinases. The protein tyrosine kinase could phosphorylate exogenous substrate corresponding to the N-terminal peptide of p34 dP 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 competitive inhibitor of the peptide binding site of mammalian protein tyrosine kinases. The enzyme activity in the cytoplasm is uniquely inhibited by sodium orthovanadate (IC SH =20 WM) which is a known protein tyrosine phosphatase inhibitor. The expression studies show that the enzyme is produced more at a higher temperature (22³C) of growth than at lower temperature (4³C) and during the stationary phase of growth of P. syringae. z

Psychrotolerance Mechanisms in Cold-Adapted Bacteria and their Perspectives as Plant Growth-Promoting Bacteria in Temperate Agriculture

“…The phosphate is then transferred to aspartate component of the response regulator present in the cytoplasm, which contains a DNA binding domain and a transcription activation domain (Shivaji, 2007). A similar 66 kDa cytosolic protein which was found to be phosphorylated at its tyrosine residue, was reported much earlier and may also function as a response regulator (Jagtap and Ray, 1999). The response regulator in addition acts as a transcriptional regulator and performs the function of transcription initiation of various cold expressed genes.…”

Molecular insights into the ecology of a psychrotolerant Pseudomonas syringae

“…These 30 and 85 kDa proteins phosphorylate more at higher temperature (30°C), whereas the 65 kDa protein phosphorylates only between 15 and 0°C (Ray et al ., 1994a). A 66 kDa protein was identified as a cytoplasmic tyrosine kinase that is involved in temperature sensing (Jagtap and Ray, 1999). These results indicated that temperature‐dependent phosphorylation of LPS and membrane proteins play important roles in adaptation to and growth at low temperature in P. syringae (Fig.…”