This family consists of a number of bacterial and archaeal branched-chain amino acid transport proteins. AzlD is known to be involved in conferring resistance to 4-azaleucine although its exact role is uncertain [1].

1: An lrp-like gene of Bacillus subtilis involved in branched-chain amino acid transport. Belitsky BR, Gustafsson MC, Sonenshein AL, Von Wachenfeldt C; J Bacteriol 1997;179:5448-5457. PMID:9287000