Cation specificity of osmosensing by the betaine carrier BetP of Corynebacterium glutamicum

• Published in: FEBS letters 2004-04, Vol.563 (1), p.108-112
• Main Authors: Schiller, Dirk, Krämer, Reinhard, Morbach, Susanne
• Format: Article
• Language: English
• Subjects: Amino Acid Substitution; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Betaine - metabolism; Biological Transport; Cations, Monovalent - metabolism; Corynebacterium - genetics; Corynebacterium - metabolism; Corynebacterium glutamicum; Escherichia coli; Escherichia coli - metabolism; Genetic Variation; Ion specificity; Liposomes - metabolism; Osmolar Concentration; Osmoregulator; Osmosensor; Osmotic Pressure; Potassium; Potassium - metabolism; Sensitivity and Specificity; Sodium; Sodium - metabolism; Threonine - metabolism; Water-Electrolyte Balance
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/S0014-5793(04)00279-0

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 ΔpNa +. 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.