title: Cation specificity of osmosensing by the betaine carrier BetP of Corynebacterium glutamicum.
abstract: The Na(+)/betaine carrier BetP from Corynebacterium glutamicum was purified and reconstituted in Escherichia coli phospholipid liposomes and its osmosensory properties were studied with respect to the cation specificity of osmotic activation. To dissect the influence of the co-substrate Na(+) on the energetics of uptake from its possible role as a putative trigger of osmolality-dependent BetP activation, the internal Na(+) concentration was varied without changing DeltapNa(+). Studying betaine uptake at increasing luminal Na(+) or K(+) revealed that BetP activity was triggered by Na(+) only to a negligible extent compared to activation by K(+). We conclude that activation of BetP in proteoliposomes depends solely on K(+), both in mechanistic and in physiological terms.
authors.affiliation: Institut für Biochemie der Universität zu Köln, Zülpicher Str. 47, 50674 Cologne, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schiller
authors.forename: Reinhard
authors.initials: R
authors.lastname: Krämer
authors.forename: Susanne
authors.initials: S
authors.lastname: Morbach
mesh_terms: D019943:Amino Acid Substitution; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001622:Betaine / Q000378:metabolism*; D001692:Biological Transport; D002414:Cations, Monovalent / Q000378:metabolism*; D003352:Corynebacterium / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism; D014644:Genetic Variation; D008081:Liposomes / Q000378:metabolism; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D011188:Potassium / Q000378:metabolism; D012680:Sensitivity and Specificity; D012964:Sodium / Q000378:metabolism; D013912:Threonine / Q000378:metabolism; D014882:Water-Electrolyte Balance
chemical_list: D001426:Bacterial Proteins; D002414:Cations, Monovalent; D008081:Liposomes; D013912:Threonine; D001622:Betaine; D012964:Sodium; D011188:Potassium