Role of the carboxy-terminal region of the outer membrane protein AatA in the export of dispersin from enteroaggregative Escherichia coli

Enteroaggregative Escherichia coli (EAEC) is an emerging enteric pathogen in both developing and industrialized countries. AatA, an outer-membrane protein that is a homolog of E. coli TolC, facilitates the export of the dispersin protein Aap across the outer membrane in EAEC. To identify which amino acids are important for this export activity, site-directed mutagenesis of the carboxy terminus was performed. An insertional mutant of aatA was complemented with each of several deletion mutants, and was examined for Aap secretion. The results showed that three nonpolar amino acids at positions 381-383 (Phe-Leu-Leu) were required for the activity, and these residues were located at the base of carboxy-terminal elongation in the equatorial domain of AatA.