Action of Legionella Cytolysin on Components of the Phosphokinase System of Eukaryotic Cells

Endogenous phosphorylation of specific proteins in eukaryotic cells is one of the main mechanisms controlling intracellular metabolic processes. It is proposed that microorganisms multiplying intracellularly possess ways of changing cellular metabolism to benefit their survival. The detection and partial purification of a phosphokinase system in pulmonary cells with acceptor proteins of molecular masses 150 and 55 kDa is reported. It is also shown that the bacterium Legionella pneumophila, a facultative intracellular parasite, secretes a toxic protein, cytolysin, that cleaves the 55 kDa component to produce a 45 kDa protein and probably hydrolyzes the 150 kDa component completely. Thus far, the significance of cytolysin in the pathogenesis of legionellosis has been restricted to its direct necrotic action. This product may, however, also act as a regulator of metabolic processes in the host cells by influencing their protein kinase activity. The findings reported may aid our understanding of mechanisms of intracellular parasitism and the survival strategy of pathogenic bacteria.