Abstract
Tat systems transport folded proteins across energized membranes of bacteria, archaea, and plant plastids. In Escherichia coli, TatBC complexes recognize the transported proteins, and TatA complexes are recruited to facilitate transport. We achieved an abstraction of TatA from membranes without use of detergents and observed a co-purification of PspA, a membrane-stress response protein. The N-terminal transmembrane domain of TatA was required for the interaction. Electron microscopy displayed TatA complexes in direct contact with PspA. PspB and PspC were important for the TatA-PspA contact. The activator protein PspF was not involved in the PspA-TatA interaction, demonstrating that basal levels of PspA already interact with TatA. Elevated TatA levels caused membrane stress that induced a strictly PspBC- and PspF-dependent up-regulation of PspA. TatA complexes were found to destabilize membranes under these conditions. At native TatA levels, PspA deficiency clearly affected anaerobic TMAO respiratory growth, suggesting that energetic costs for transport of large Tat substrates such as TMAO reductase can become growth limiting in the absence of PspA. The physiological role of PspA recruitment to TatA may therefore be the control of membrane stress at active translocons.
Highlights
The Tat translocon transports folded proteins across energized prokaryotic cytoplasmic membranes
E. coli TatA Interacts with phage shock protein A (PspA)—TatA is membrane-anchored by a single N-terminal transmembrane domain (TMD) and a subsequent amphipathic helix that associates with the membrane [17, 34]
The only TatA interaction partner identified by Coomassiestained SDS-PAGE and mass spectrometry was PspA, which is a coiled-coil protein that forms multimeric complexes that stabilize cytoplasmic membranes under stress conditions [39]
Summary
The Tat translocon transports folded proteins across energized prokaryotic cytoplasmic membranes. Results: The N-terminal transmembrane domain of TatA interacts with the membrane-stabilizing Psp machinery. Conclusion: Membrane-stabilization takes place where folded proteins are Tat-dependently translocated. Tat systems transport folded proteins across energized membranes of bacteria, archaea, and plant plastids. The activator protein PspF was not involved in the PspATatA interaction, demonstrating that basal levels of PspA already interact with TatA. Elevated TatA levels caused membrane stress that induced a strictly PspBC- and PspF-dependent up-regulation of PspA. At native TatA levels, PspA deficiency clearly affected anaerobic TMAO respiratory growth, suggesting that energetic costs for transport of large Tat substrates such as TMAO reductase can become growth limiting in the absence of PspA. The physiological role of PspA recruitment to TatA may be the control of membrane stress at active translocons
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