Serine/threonine protein kinases PknF and PknG of Mycobacterium tuberculosis: characterization and localization

Pathogenesis of Mycobacterium tuberculosis is closely connected to its surv ival and replication within the host. Some pathogenic bacteria employ prote in kinases that interfere with the cellular signalling network of host cell s and promote bacterial survival. In this study, the pknF and pknG genes, w hich encode two putative protein kinases of M. tuberculosis H(37)Rv, protei n kinase F (PknF) and protein kinase G (PknG), respectively, were cloned an d expressed in Escherichia coli. Purified PknF phosphorylated the peptide s ubstrate myelin basic protein (MBP) at serine and threonine residues, while purified PknG phosphorylated only at serine residues. The activity of the two kinases was abrogated by mutation of the codon for the predicted ATP-bi nding-site lysine residue. Southern blot analysis revealed that homologues of the genes encoding the two kinases are present in M. tuberculosis H37Ra and Mycobacterium bovis BCG, but not in Mycobacterium smegmatis. Immunoblot analysis of various cellular fractions of M. tuberculosis H(37)Rv revealed that PknF is a transmembrane protein and that PknG is predominantly a cyto solic enzyme. The present study should aid in elucidating the role of these protein kinases in the pathogenesis of mycobacteria.