Part of a high affinity multicomponent binding-protein-dependent transport system involved in bacterial osmoregulation. This domain is often fused to the permease component of the transporter complex. Family members are often integral membrane proteins or predicted to be attached to the membrane by a lipid anchor. Glycine betaine is involved in protection from high osmolarity environments for example in Bacillus subtilis [1]. The family member OpuBC is closely related, and involved in choline transport. Choline is necessary for the biosynthesis of glycine betaine [2]. L-carnitine is important for osmoregulation in Listeria monocytogenes. Family also contains proteins binding l-proline (ProX), histidine (HisX) and taurine (TauA).

1: OpuA, an osmotically regulated binding protein-dependent transport system for the osmoprotectant glycine betaine in Bacillus subtilis. Kempf B, Bremer E; J Biol Chem 1995;270:16701-16713. PMID:7622480

2: Two evolutionarily closely related ABC transporters mediate the uptake of choline for synthesis of the osmoprotectant glycine betaine in Bacillus subtilis. Kappes RM, Kempf B, Kneip S, Boch J, Gade J, Meier-Wagner J, Bremer E; Mol Microbiol 1999;32:203-216. PMID:10216873

3: Identification and characterization of an ATP binding cassette L-carnitine transporter in Listeria monocytogenes. Fraser KR, Harvie D, Coote PJ, O'Byrne CP; Appl Environ Microbiol 2000;66:4696-4704. PMID:11055912