Initial assembly steps of a translocase for folded proteins

Area of Science:

• Molecular Biology
• Cellular Biology
• Protein Transport Mechanisms

Background:

• The twin-arginine translocation (Tat) system is crucial for transporting fully folded proteins across membranes in various organisms.
• Tat system function relies on membrane proteins TatA, TatB, and TatC, with TatB and TatC known to interact with RR-signal peptides.
• Understanding the oligomeric structure of TatBC is key to elucidating the mechanism of Tat-mediated protein transport.

Purpose of the Study:

• To elucidate the detailed architecture of TatBC oligomers.
• To understand how TatBC complexes form intramembrane substrate-binding cavities.
• To investigate the interaction of TatA with the TatBC complex and substrate precursors.

Main Methods:

• Structural analysis of TatBC oligomers.
• Identification of specific homonymous and heteronymous contacts between TatB and TatC proteins.
• Investigation of TatA protomer interactions with the TatBC complex.

Main Results:

• TatBC oligomers form closed intramembrane substrate-binding cavities.
• TatB monomers assemble into dome-like structures enclosed by TatC monomer rings.
• TatA protomers interact with TatB via their N-termini, contacting membrane-inserted RR-precursors.

Conclusions:

• The study reveals the precise architecture of the TatBC complex, essential for substrate binding and transport initiation.
• The findings provide a structural basis for understanding how the Tat system recognizes and binds twin-arginine signal peptides.
• The interaction model clarifies the roles of TatA, TatB, and TatC in the overall Tat protein translocation pathway.