Three transport systems for the osmoprotectant glycine betaine operate in Bacillus subtilis: characterization of OpuD.

摘要: The accumulation of the osmoprotectant glycine betaine from exogenous sources provides a high degree osmotic tolerance to Bacillus subtilis. We have identified, through functional complementation an Escherichia coli mutant defective in uptake, new transport system B. DNA sequence 2,310-bp segment cloned region revealed single gene (opuD) whose product (OpuD) was essential for uptake and osmoprotection E. coli. opuD encodes hydrophobic 56.13-kDa protein (512 amino acid residues). OpuD shows significant identity choline transporter BetT carnitine CaiT BetT-like Haemophilus influenzae. These membrane proteins form family transporters involved trimethylammonium compounds. OpuD-mediated activity subtilis is controlled by environmental osmolarity. High osmolarity stimulates de novo synthesis activates preexisting achieve maximal activity. An constructed marker replacement, compared with that previously identified multicomponent OpuA OpuC (ProU) systems. In addition, set mutants constructed, each which synthesized only one three were used determine kinetic parameters OpuA, OpuC, OpuD. Each these systems substrate affinity, Km values low micromolar range, should allow efficiently acquire environment. differed their contribution overall osmoprotection. A triple opuA, opuC, strain isolated, it showed no activity, demonstrating this operate