Invasion activity of a Mycobacterium tuberculosis peptide presented by the Escherichia coli AIDA autotransporter

The mce1A gene of Mycobacterium tuberculosis was initially identified by its ability to promote uptake of Escherichia coli into HeLa cells. It was subsequently shown that this activity was confined to a 58-amino-acid region of the protein. A 72-amino-acid fragment (InvX) incorporating this active peptide was expressed in E. coli as a fusion to the AIDA (adhesin involved in diffuse adherence) autotransporter translocator, and its stable expression on the surface of the bacterium was demonstrated. Recombinant E. coli expressing InvX-AIDA showed extensive association with HeLa cells, and InvX was shown to be sufficient for internalization. Uptake was found to be both microtubule and microfilament dependent and required the Rho family of GTPases. Thus, the E. coli AIDA system facilitated both the qualitative and quantitative analysis of the functional domain of a heterologous protein.