Open AccessCholine Uptake in Agrobacterium tumefaciens by the High-Affinity ChoXWV Transporter
Author(s) -
Meriyem Aktas,
Kathinka A. Jost,
Christiane Fritz,
Franz Narberhaus
Publication year - 2011
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.05421-11
Subject(s) - agrobacterium tumefaciens , biology , biochemistry , choline , phosphatidylcholine , operon , stereochemistry , mutant , phospholipid , chemistry , membrane , transformation (genetics) , gene
Agrobacterium tumefaciens is a facultative phytopathogen that causes crown gall disease. For successful plant transformationA. tumefaciens requires the membrane lipid phosphatidylcholine (PC), which is produced via the methylation and the PC synthase (Pcs) pathways. The latter route is dependent on choline. Although choline uptake has been demonstrated inA. tumefaciens , the responsible transporter(s) remained elusive. In this study, we identified the first choline transport system inA. tumefaciens . The ABC-type choline transporter is encoded by the chromosomally locatedchoXWV operon (ChoX, binding protein; ChoW, permease; and ChoV, ATPase). The Cho system is not critical for growth and PC synthesis. However, [14 C]choline uptake is severely reduced inA. tumefaciens choX mutants. Recombinant ChoX is able to bind choline with high affinity (equilibrium dissociation constant [KD ] of ≈2 μM). Since other quaternary amines are bound by ChoX with much lower affinities (acetylcholine,KD of ≈80 μM; betaine,KD of ≈470 μM), the ChoXWV system functions as a high-affinity transporter with a preference for choline. Two tryptophan residues (W40 and W87) located in the predicted ligand-binding pocket are essential for choline binding. The structural model of ChoX built onSinorhizobium meliloti ChoX resembles the typical structure of substrate binding proteins with a so-called “Venus flytrap mechanism” of substrate binding.