The Hairpin‐Hinge Model of Tat Protein Transport

Abstract

The bacterial twin arginine translocation (Tat) pathway transports folded proteins across the cytoplasmic membrane. Biochemical evidence indicates that the TatBC receptor complex contains the signal peptide binding site and the interaction of the signal peptide with this complex triggers the assembly of a translocation channel. However, it is unclear how the signal peptide interacts with the receptor complex and how it enables the movement of cargo through the channel. Here we show using fluorescence quenching and disulfide crosslinking that TatBC complex inserts pre‐SufI as a hairpin that extends about half‐way across the membrane. Photo crosslinking studies indicated that the c‐terminal of the hairpin interacts with TatB. Furthermore, computational analysis of ~500 Tat signal peptides and docking simulations of TatBC and pre‐SufI revealed 3 common features of the hairpin structure: 1) a helical structure; 2) a helix destabilizing residue; and 3) a relatively disordered domain. A hinge motion at the hairpin bend would allow the signal peptide to be bound to TatC surface via double arginines (n‐terminal) and allow the cleavage site (c‐terminal) to migrate to the periplasmic side. Disulfide crosslinking of n‐ and c‐terminal hairpin ends inhibited the transport of the cargo suggesting a novel Hairpin‐Hinge Translocation for Tat pathwaySupport or Funding InformationNIH Grant GMO65534