The prototype of this family, FmdC, is a porin involved in the transport of short-chain amides and urea through the outer membrane of Methylophilus methylotrophus under conditions where these nitrogen sources are present at a very low concentration. Its synthesis is inducible by short-chain amides and urea and the protein is believed to transport these molecules across the outer membrane. Homologs are found in a variety of Gram-negative bacteria, like Geobacter sulfurreducens, Geobacter metallireducens, Methylobacillus flagellatus and Aquifex aeolicus. The AQ_1862 from Aquifex aeolicus has been shown to be outer membrane-localized and to possess channel properties.