Omp_AT is a family of Gram-negative Gamma-proteobacteria outer membrane autotransporter ß-barrel proteins. Secondary structure prediction indicates a ß-barrel domain of 12 beta-strands. with an N terminal helix running along the central barrel axis perpendicular to the 12 antiparallel strands that form the barrel. Autotransporter translocation units defined by a ß-barrel of 12 to 14 antiparallel strands with an N terminal helix perpendicular to the barrel.