Bioenergetic requirements of a Tat-dependent substrate in the halophilic archaeon Haloarcula hispanica

Twin-arginine translocase (Tat) is involved in the translocation of fully folded proteins in a process that is driven by the proton motive force. In most prokaryotes, the Tat system transports only a small proportion of secretory proteins, and Tat substrates are often cofactor-containing proteins that require folding before translocation. A notable exception is found in halophilic archaea (haloarchaea), which are predicted to secrete the majority of their proteins through the Tat pathway. In this study, we have analysed the translocation of a secretory protein (AmyH) from the haloarchaeon Haloarcula hispanica. Using both in vivo and in vitro translocation assays, we demonstrate that AmyH transport is Tat-dependent, and, surprisingly, that its secretion does not depend on the proton motive force but requires the sodium motive force instead.