FomA is the designation given to a small family of sequence similar outer membrane porins from F. nucleatum. They are trimeric proteins, each subunit exhibiting 14 C-terminal antiparallel transmembrane β-strands connected to an N-terminal periplasmic domain (Puntervoll et al., 2002). An external loop, L6, the largest of the seven such loops, when deleted renders FomA more permeable to antibiotics. L6 probably folds back into the β-barrel, thereby constricting the pore. FomA porins lack significant sequence similarity to other known porins, but they do exhibit similar structural features. They transport solutes non-specifically except for a size limit. Deletion of L6 increases this size limit.

The transport reaction catalyzed by FomA porins is:

solute (out) solute (periplasm)