Abstract

The twin arginine translocation (Tat) system is an integral membrane protein complex that accomplishes the remarkable feat of transporting large, fully-folded polypeptides across the inner membrane of bacteria, into the periplasm. In Escherichia coli Tat is comprised of three membrane proteins: TatA, TatB and TatC. How these proteins arrange themselves in the inner membrane to permit passage of Tat substrates, whilst maintaining membrane integrity, is still poorly understood. TatA is the most abundant component of this complex and facilitates assembly of the transport mechanism. We have utilised immunogold labelling in combination with array tomography to gain insight into the localisation and distribution of the TatA protein in E. coli cells. We show that TatA exhibits a uniform distribution throughout the inner membrane of E. coli and that altering the expression of TatBC shows a previously uncharacterised distribution of TatA in the inner membrane. Array tomography was used to provide our first insight into this altered distribution of TatA in 3D space, revealing that this protein forms linear clusters in the inner membrane of E. coli upon increased expression of TatBC. This is the first indication that TatA organisation in the inner membrane alters in response to changes in Tat subunit stoichiometry.\n\nSummary statementThe volumetric electron-microscopy technique, array tomography, revealed a novel distribution of TatA protein (from the twin arginine translocase complex), in Escherichia coli.