Evidence that a eukaryotic‐type serine/threonine protein kinase from Mycobacterium tuberculosis regulates morphological changes associated with cell division

A eukaryotic‐type protein serine/threonine kinase, PknA, was cloned from Mycobacterium tuberculosis strain H37Ra. Sequencing of the clone indicated 100% identity with the published pknA sequence of M. tuberculosis strain H37Rv. PknA fused to maltose‐binding protein was expressed in Escherichia coli; it exhibited a molecular mass of ≈ 97 kDa. The fusion protein was purified from the soluble fraction by affinity chromatography using amylose resin. In vitro kinase assays showed that the autophosphorylating ability of PknA is strictly magnesium/manganese‐dependent, and sodium orthovanadate can inhibit this activity. Phosphoamino‐acid analysis indicated that PknA phosphorylates at serine and threonine residues. PknA was also able to phosphorylate exogenous substrates, such as myelin basic protein and histone. A comparison of the nucleotide‐derived amino‐acid sequence of PknA with that of functionally characterized prokaryotic serine/threonine kinases indicated its possible involvement in cell division/differentiation. Protein–protein interaction studies revealed that PknA is capable of phosphorylating at least a ≈56‐kDa soluble protein from E. coli. Scanning electron microscopy showed that constitutive expression of this kinase resulted in elongation of E. coli cells, supporting its regulatory role in cell division.