Members of this family are predicted multiple membrane-spanning proteins, and therefore thought likely to be transporters. It appears that all species whose genomes encode a member of this family produce selenocysteine-containing enzymes, typically formate dehydrogenase. The family member from Campylobacter jejuni was show to be essential for formate dehydrogenase (a selenocysteine-containing enzyme) expression and activity, and so it was named a formate dehydrogenase accessory protein, FdhT. Note that this family is related to (but distinct from) that of TIGR04112, which is similarly restricted to species with pathways for selenium incorporation.
Jiyao W et al.(2023). "The conserved domain database in 2023.",