Crystal structure of the transport unit of the autotransporter adhesin involved in diffuse adherence from Escherichia coli.

Several serious gastrointestinal diseases, which are widespread all over the world, are caused by enteropathogenic Escherichia coli. 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.

Purification, crystallization and preliminary X-ray crystallographic analysis of the transport unit of the monomeric autotransporter AIDA-I from Escherichia coli.

The adhesin involved in diffuse adherence (AIDA-I) from Escherichia coli belongs to the group of autotransporters, specifically the type Va secretion system (T5aSS). All autotransporter systems contain a C-terminal β-domain, which forms a barrel-like structure in the outer membrane with a hydrophilic pore allowing passenger translocation across the outer membrane. The passenger domain harbours the biological activity in the extracellular space and functions, for example, as an adhesin, an enzyme and a toxin.

Structural comparison of the transport units of type V secretion systems.

Pathogenic gram-negative bacteria have evolved several secretion mechanisms to translocate adhesins, enzymes, toxins, and other virulence factors across the inner and outer membranes. Currently, eight different secretion systems, type I-type VIII (T1SS-T8SS) plus the chaperone-usher (CU) pathway, have been identified, which act in one-step or two-step mechanisms to traverse both membrane barriers. The type V secretion system (T5SS) is dependent first on the Sec translocon within the inner membrane.