High-affinity uptake of glycine betaine, driven by a sodium-motive force. Involved, with GbuABC and OpuC, in osmoprotection and cryoprotection of Listeria. Does not mediate either carnitine or choline uptake. Activated rapidly in response to an osmotic upshift. Constitutively expressed. Up-regulated in response to salt stress and cold shock. Mutants show a strong decrease in the rate of glycine betaine uptake. Mutation does not significantly affect cryoprotection or virulence of the organism, probably due to the presence of other glycine betaine/carnitine transporters in the cell. Activation of preexisting BetL protein in response to relatively low salt concentrations represents the most immediate response of the cell to increased salinity. GbuABC system is most important during prolonged exposure (PubMed:14645273). Belongs to the BCCT transporter (TC 2.A.15) family.