Sugar Binding Induced Charge Translocation in the Melibiose Permease from Escherichia coli

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• 作者：Kerstin Meyer-Lipp ; Constanta Ganea ; Thierry Pourcher ; Gé ; rard Leblanc ; and Klaus Fendler
• 刊名：Biochemistry
• 出版年：2004
• 出版时间：October 5, 2004
• 年：2004
• 卷：43
• 期：39
• 页码：12606 - 12613
• 全文大小：104K
• 年卷期：v.43,no.39(October 5, 2004)
• ISSN：1520-4995

文摘

Electrogenic events associated with the activity of the melibiose permease (MelB), a transporterfrom Escherichia coli, were investigated. Proteoliposomes containing purified MelB were adsorbed to asolid supported lipid membrane, activated by a substrate concentration jump, and transient currents weremeasured. When the transporter was preincubated with Na⁺ at saturating concentrations, a chargetranslocation in the protein upon melibiose binding could still be observed. This result demonstrates thatbinding of the uncharged substrate melibiose triggers a charge displacement in the protein. Further analysisshowed that the charge displacement is neither related to extra Na⁺ binding to the transporter, nor to thedisplacement of already bound Na⁺ within the transporter. The electrogenic melibiose binding process isexplained by a conformational change with concomitant displacement of charged amino acid side chainsand/or a reorientation of helix dipoles. A kinetic model is suggested, in which Na⁺ and melibiose bindingare distinct electrogenic processes associated with approximately the same charge displacement. Thesebinding reactions are fast in the presence of the respective cosubstrate (k > 50 s^-1).