The Inverse Autotransporter Intimin Exports its Passenger Domain via a Hairpin Intermediate [Protein Structure and Folding]

December 8th, 2014 by Oberhettinger, P., Leo, J. C., Linke, D., Autenrieth, I. B., Schutz, M. S.

Autotransporter proteins comprise a large family of virulence factors which consist of a β-barrel translocation unit and an extracellular effector or passenger domain. The β-barrel anchors the protein to the outer membrane of Gram-negative bacteria and facilitates the transport of the passenger domain onto the cell surface. By inserting an epitope tag into the N-terminus of the passenger domain of the inverse autotransporter Intimin, we generated a mutant defective in autotransport. Using this stalled mutant we could show that (I) at the timepoint of stalling the β-barrel appears folded, (II) the stalled autotransporter is associated with BamA and SurA, (III) the stalled Intimin is decorated with large amounts of SurA, (IV) the stalled autotransporter is not degraded by periplasmic proteases, and that (V) inverse autotransporter passenger domains are translocated by a hairpin mechanism. Our results suggest a function for the BAM complex not only in insertion and folding of the β-barrel but also for passenger translocation.