Adhesin (Hia) The 3-d structure is available (PDB#2GR7). Mediates bacterial adhesion to the respiratory epithelium. The crystal structure of the C-terminal end of Hia, corresponding to the entire Hia translocator domain and part of the passenger domain (residues 992-1098) shows that this domain forms a beta-barrel with 12 transmembrane beta-strands, including four strands from each subunit. The beta-barrel has a central channel of 1.8 nm in diameter that is traversed by three N-terminal alpha-helices, one from each subunit. Mutagenesis studies demonstrated that the transmembrane portion of the three alpha-helices and the loop region between the alpha-helices and the neighboring beta-strands are essential for stability, and that trimerization of the translocator domain is a prerequisite for translocator activity (Meng et al. 2006).  Electrostatic repulsion between the positive charges of Arg1077 is important to prevent the formation of misassembled oligomers by the Hia transmembrane domain in vitro (Aoki et al. 2017).