Efficient membrane assembly of the KcsA potassium channel in Escherichia coli requires the protonmotive force

Very little is known about the biogenesis and assembly of oligomeric membra ne proteins. In this study, the biogenesis of KcsA, a prokaryotic homotetra meric potassium channel, is investigated. Using in vivo pulse-chase experim ents, both the monomeric and tetrameric form could be identified. The conve rsion of monomers into a tetramer is found to be a highly efficient process that occurs in the Escherichia coil inner membrane. KcsA does not require ATP hydrolysis by SecA for insertion or tetramerization. The presence of th e protonmotive force (pmf) is not necessary for transmembrane insertion of KcsA; however, the pmf proved to be essential for the efficiency of oligome rization. From in vivo and in vitro experiments ii is concluded that the el ectrical component, Delta psi, is the main determinant for this effect. The se results demonstrate a new role of the pmf in membrane protein biogenesis .