Moving Folded Proteins Across Membranes: a Tale of Two Transporters

Proteins are generally assumed to be transported across membranes in an unfolded state. However, it is becoming increasingly apparent that there are also transporters dedicated to moving folded proteins through membranes. We have identified two such systems in bacteria. The Tat (twin-arginine translocation) system is found in the bacterial cytoplasmic membrane and conserved in some eukaryotic organelles. The Type 9 Secretion System is found in the outer membrane of bacteria from the Bacteroidetes superphylum. Both transport systems are essential virulence determinants in human pathogens. I will describe our latest data on these transport systems and show that they transport folded proteins by very different mechanisms.