Several serious gastrointestinal diseases, which are widespread all over the world, are caused by enteropathogenic Escherichia coil. The monomeric autotransporter AIDA-I (adhesin involved in diffuse adherence) represents an important virulence factor of these strains and is involved in adhesion, biofilm formation, aggregation and invasion into host cells. Here, we present the crystal structure of the transport unit of AIDA-I at 3.0 angstrom resolution, which forms a 12-stranded beta-barrel harboring the linker domain in its pore. Mutagenesis studies of the C-terminal amino acid demonstrated the great impact of this terminal residue on membrane integration of AIDA-I and passenger translocation. (C) 2014 Elsevier Inc. All rights reserved.