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The Tat system mediates Sec-independent transport of folded precursor proteins across the bacterial plasma membrane or the chloroplast thylakoid membrane. Tat transport involves distinct high-molecular-weight TatA and TatBC complexes. Here we report the 3D architecture of the TatA complex from Escherichia coli obtained by single-particle electron microscopy and random conical tilt reconstruction. TatA forms ring-shaped structures of variable diameter in which the internal channels are large enough to accommodate known Tat substrate proteins. This morphology strongly supports the proposal that TatA forms the protein-conducting channel of the Tat system. One end of the channel is closed by a lid that might gate access to the channel. On the basis of previous protease accessibility measurements, the lid is likely to be located at the cytoplasmic side of the membrane. The observed variation in TatA diameter suggests a model for Tat transport in which the number of TatA protomers changes to match the size of the channel to the size of the substrate being transported. Such dynamic close packing would provide a mechanism to maintain the membrane permeability barrier during transport.

Original publication

DOI

10.1073/pnas.0503558102

Type

Journal article

Journal

Proc Natl Acad Sci U S A

Publication Date

26/07/2005

Volume

102

Pages

10482 - 10486

Keywords

Escherichia coli, Escherichia coli Proteins, Image Processing, Computer-Assisted, Membrane Transport Proteins, Microscopy, Electron, Models, Molecular, Protein Conformation