Type V Protein Secretion: Simplicity Gone Awry?

Since its discovery in the late 1980's, the family of secreted proteins termed the autotransporters has been expanding continuously to become the largest group of secreted proteins in Gram-negative bacteria. The type V secretion pathway, which includes the autotransporters (type V a ) together with the twopartner secretion system (type V b ) and the Oca family (type V c ), can be defi ned by secreted proteins that are (i) translocated across the outer membrane via a transmembrane pore formed by a -barrel and (ii) contain all the information required for translocation through the cell envelope. In the light of new discoveries and controversies in this research fi eld, the secretion process of autotransporters, or the type V a secretion system, will be discussed here and placed in the context of the more general fi eld of bacterial protein translocation.