Secretion of protein products occurs by a number of different pathways in bacteria. One of these pathways known as the type IV pathway was first described for the IgA1 protease. The protein component that mediates secretion through the outer membrane is contained within the secreted protein itself, hence the proteins secreted in this way are called autotransporters. This family corresponds to the presumed integral membrane beta-barrel domain that transports the protein. This domain is found at the C-terminus of the proteins it occurs in. The N-terminus contains the variable passenger domain that is translocated across the membrane. Once the passenger domain is exported it is cleaved auto-catalytically in some proteins, in others a different peptidase is used and in some cases no cleavage occurs.
Jiyao W et al.(2023). "The conserved domain database in 2023.",