A new way out: protein localization on the bacterial cell surface via Tat and a novel Type II secretion system.

The ability to move proteins out of the cytoplasm and across membranes is a key aspect of the physiology and pathogenicity of Gram-negative bacteria. In this issue of Molecular Microbiology, Ferrandez and Condemine describe a novel protein targeting system in the enteric phytopathogen, Dickeya dadantii. The pectin lyase, PnlH, is exported by the Tat system and is somehow targeted to the outer membrane by its uncleaved N-terminal Tat signal anchor. A novel Type II secretion system, Stt, is then responsible for moving it across the outer membrane, where it remains localized on the surface of the cell. We discuss the implications of these findings for our understanding of both the mechanisms and physiological importance of bacterial protein targeting.