Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 105, Issue 40, Pages 15376-15381Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0806338105
Keywords
fluorescence; Tat protein transport
Categories
Funding
- Biotechnology and Biological Sciences Research Council [D004578]
- Leverhulme Trust
- Royal Society University
- Royal Society
- Research Councils U.K.
- Wellcome Trust [061780]
- Medical Research Council
- BBSRC [BB/D011140/2, BB/E00458X/1, BB/D004578/1, BB/D011140/1] Funding Source: UKRI
- MRC [G117/519] Funding Source: UKRI
- Biotechnology and Biological Sciences Research Council [BB/D004578/1, BB/D011140/1, BB/D011140/2, BB/E00458X/1] Funding Source: researchfish
- Medical Research Council [G117/519] Funding Source: researchfish
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The twin-arginine translocation (Tat) system transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membrane of plant chloroplasts. The essential components of the Tat pathway are the membrane proteins TatA, TatB, and TatC. TatA is thought to form the protein translocating element of the Tat system. Current models for Tat transport make predictions about the oligomeric state of TatA and whether, and how, this state changes during the transport cycle. We determined the oligomeric state of TatA directly at native levels of expression in living cells by photophysical analysis of individual yellow fluorescent protein-labeled TatA complexes. TatA forms complexes exhibiting a broad range of stoichiometries with an average of approximate to 25 TatA subunits per complex. Fourier analysis of the stoichiometry distribution suggests the complexes are assembled from tetramer units. Modeling the diffusion behavior of the complexes suggests that TatA protomers associate as a ring and not a bundle. Each cell contains approximate to 15 mobile TatA complexes and a pool of approximate to 100 TatA molecules in a more disperse state in the membrane. Dissipation of the protonmotive force that drives Tat transport has no affect on TatA complex stoichiometry. TatA complexes do not form in cells lacking TatBC, suggesting that TatBC controls the oligomeric state of TatA. Our data support the TatA polymerization model for the mechanism of Tat transport.
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