Antigen 43 (Ag43), the product of the flu gene, is a cell-surface autotransporter protein found in Escherichia coli. It is expressed at about 50, 000 copies/cell and is initially synthesised as a precursor of 1039 amino acids. Upon removal of the signal peptide, the protein is transported to the cell surface and is composed of an α subunit (499 amino acids) at the N-terminus and a β subunit (488 amino acids) at the C-terminus. Ag43 is mainly known to induce cell-to-cell aggregation and be involved in biofilm formation. However, as the necessary information required for auto transportation resides in the protein itself, the main of our project was to use it as a platform for displaying specific peptides on the surface of E. coli.