The ATP-binding cassette transporter Cbc (choline/betaine/carnitine) recruits multiple substrate-binding proteins with strong specificity for distinct quaternary ammonium compounds

Abstract

Summary We identified a choline, betaine and carnitine transporter, designated Cbc, from Pseudomonas syringae and Pseudomonas aeruginosa that is unusual among members of the ATP-binding cassette (ABC) transporter family in its use of multiple periplasmic substrate-binding proteins (SBPs) that are highly specific for their substrates. The SBP encoded by the cbcXWV operon, CbcX, binds choline with a high affinity (Km, 2.6 μM) and, although it also binds betaine (Km, 24.2 μM), CbcXWV-mediated betaine uptake did not occur in the presence of choline. The CbcX orthologue ChoX from Sinorhizobium meliloti was similar to CbcX in these binding properties. The core transporter CbcWV also interacts with the carnitine-specific SBP CaiX (Km, 24 μM) and the betaine-specific SBP BetX (Km, 0.6 μM). Unlike most ABC transporter loci, caiX, betX and cbcXWV are separated in the genome. CaiX-mediated carnitine uptake was reduced by CbcX and BetX only when they were bound by their individual ligands, providing the first in vivo evidence for a higher affinity for ligand-bound than ligand-free SBPs by an ABC transporter. These studies demonstrate not only that the Cbc transporter serves as a useful model for exploring ABC transporter component interactions, but also that the orphan SBP genes common to bacterial genomes can encode functional SBPs.

Homeostasis and Catabolism of Choline and Glycine Betaine: Lessons from Pseudomonas aeruginosa

“…1), while these solutes have specialized periplasmic binding subunits (CbcX, BetX, and CaiX, respectively) (47). The periplasmic solute binding proteins use a ligand binding site similar to that for compatible solute receptors in other bacteria (69,70).…”

“…GbdR induces transcription in response to GB and dimethylglycine in the cytosol, leading to induction of choline and GB acquisition components (plcH, pchP, cbcXWV, and betX) and induction of the components of the GB catabolic pathway (gbcA and -B, the dgc operon, soxBDAG, glyA1, and sdaB) (47,48,56,(64)(65)(66)(67) (Fig. 2).…”

Bacterial biosynthesis of 1-aminocyclopropane-1-caboxylate (ACC) deaminase, a useful trait to elongation and endophytic colonization of the roots of rice under constant flooded conditions

“…To monitor rice root and tissue colonization by this isolate and since rice seeds can be an important source of endophytic bacteria (Kaga et al 2009), we marked P. fluorescence REN 1 with gusA. Briefly for this purpose, Escherichia coli DH5α containing transposon-based b-glucuronidase (GUS) marker pNpt, which has the gusA gene under the control of a constitutive tetracycline and ampicillin resistance gene promoter (Chen et al 2010), was maintained on Luria agar plates. For generation of the GUStagged strain, pNpt-GUS was transferred to P. fluorescence REN 1 using the triparental mating method (Ditta et al 1980).…”

Trimethylamine N -oxide metabolism by abundant marine heterotrophic bacteria

“…They usually consist of three subunits: a transmembrane domain that is bound to an inner membranebound ATP-binding domain and a periplasmic substrate-binding protein (SBP), which binds a given ligand. SBPs confer substrate specificity and can bind their ligands with very high affinity (19,20). One group of ABC transporters specialize in the uptake of compatible osmolytes and structurally related compounds, such as glycine betaine (GBT), choline, carnitine, and proline betaine (21,22).…”

“…One group of ABC transporters specialize in the uptake of compatible osmolytes and structurally related compounds, such as glycine betaine (GBT), choline, carnitine, and proline betaine (21,22). These transporters either function in osmoregulation (23) or play a role in substrate catabolism (19). A bacterial ATPdependent TMAO transporter has been identified (24), but the genes encoding this transport system are unknown.…”