Purification and Crystallization of the His-tagged AIDA-I ß-barrel in the outer membrane of E. coli

AIDA-I, the adhesin-involved-in-diffuse-adherence glycoprotein is a virulence factor of the enteropathogenetic E. coli and is involved in gastrointestinal diseases [1]. This protein belongs to the group of autotransporter proteins, a large family of self-translocation proteins in gram-negative bacteria. Typically autotransporter proteins consist of four functional domains: a signal-peptide domain, which mediates the translocation across the cytoplasmic membrane, a passenger domain, which encodes the exposed protein, a linker domain, which helps the passenger domain crossing the outer membrane and the β-barrel-domain, which forms a porin-like structure in the outer membrane [2]. The molecular mechanism of the translocation and folding processes and also the structure of the AIDA-I β barrel are still largely unknown. With the help of the Autodisplay system which is based on the secretion mechanism of autotransporter proteins [3] it is possible to translocate recombinant proteins across both lipid bilayers of E. coli. This effective surface display system was used to express high amounts of the AIDA-I fusion protein of the recent studies. Here we show the expression and purification using affinity chromatography via the hexahistidin-tag and initial steps in the crystallization of an AIDA-I fusion protein.