Post-modern pathogens: surprising activities of translocated effectors from E. coli and Legionella.

Many bacterial pathogens have the ability to manipulate cellular processes and interfere with host cell function through the translocation of bacterial ‘effector’ proteins. Dedicated protein secretion machines from Gram-negative pathogens, including type III, type IV and type VI secretion systems, inject virulence proteins into infected cells, altering normal cell physiology, including cell structure, metabolism, trafficking and signalling. While effectors were once thought to exert an effect simply by their localization and binding to host cell proteins, increasingly effectors are being recognised as enzymes, in some cases mediating highly novel post-translational modifications on host proteins. Here we highlight some of the more unusual activities of translocated effectors from enteropathogenic Escherichia coli and Legionella pneumophila .