The members of this family are similar to a region of the protein product of the bacterial tadE locus (Swiss:Q9S4A6). In various bacterial species, the tad locus is closely linked to flp-like genes, which encode proteins required for the production of pili involved in adherence to surfaces [1]. It is thought that the tad loci encode proteins that act to assemble or export an Flp pilus in various bacteria [1]. All tad loci but TadA have putative transmembrane regions [1], and in fact the region in question is this family has a high proportion of hydrophobic amino acid residues.

1: Genes for tight adherence of Actinobacillus actinomycetemcomitans: from plaque to plague to pond scum. Kachlany SC, Planet PJ, DeSalle R, Fine DH, Figurski DH; Trends Microbiol 2001;9:429-437. PMID:11553455