Involved in virulence. Mediates adherence to human respiratory epithelial cells. Homotrimer. The C-terminal translocator domain is localized in the outer membrane and the passenger domain is at the cell surface. Expressed in vivo during the course of aerosol infection. Expressed at very low levels under routine laboratory growth conditions. Contains a well-conserved 23 amino acid extended signal peptide region (ESPR) preceding a typical N-terminal signal sequence. ESPR region may be involved in regulating the translocation of the autotransporter across the inner membrane into the periplasm. The signal peptide, cleaved at the inner membrane, guides the autotransporter protein to the periplasmic space. Then, insertion of the C-terminal translocator domain in the outer membrane forms a hydrophilic pore for the translocation of the passenger domain to the bacterial cell surface. Inactivation of the gene substantially reduces adherence to monolayers of HEp-2 laryngeal cells and A549 type II pneumocytes, as well as to cultures of normal human bronchial epithelium (NHBE). Mutation does not affect the virulence in a mouse model of aerosol infection. Belongs to the autotransporter-2 (AT-2) (TC 1.B.40) family.