TatB functions as an oligomeric binding site for folded Tat precursor proteins

Area of Science:

• Molecular Biology
• Cellular Transport
• Protein Folding

Background:

• The twin-arginine translocation (Tat) pathway facilitates the transport of folded proteins across membranes.
• The Escherichia coli Tat machinery comprises TatA, TatB, and TatC membrane proteins.
• While Tat signal peptide recognition by TatB and TatC is understood, interactions with folded protein domains remain unclear.

Purpose of the Study:

• To investigate the molecular interactions between folded Tat substrates and the Tat machinery.
• To identify the role of TatB in binding mature, folded Tat precursor proteins.

Main Methods:

• Utilized photo-cross-linking in Tat substrates at various positions within folded proteins.
• Targeted cross-linked variants to the Tat machinery in membrane vesicles.
• Incorporated photo-cross-linkers into TatB to map precursor-binding sites.

Main Results:

• Surface-exposed cross-linking sites on Tat substrates showed proximity to TatB.
• TatB revealed multiple precursor-binding sites within its transmembrane and amphipathic helices.
• Evidence of TatB oligomers interacting with single precursor molecules was observed.
• Cross-linking required an intact twin-arginine signal peptide and ceased upon translocation.

Conclusions:

• TatB forms an oligomeric binding site for folded Tat precursors.
• This site transiently accommodates proteins during their translocation via the Tat machinery.