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A structural investigation of bacterial twin-arginine translocation (tat) complexes by single-particle electron microscopy
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Beck, Daniel K. (2012) A structural investigation of bacterial twin-arginine translocation (tat) complexes by single-particle electron microscopy. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2672364~S1
Abstract
The Twin arginine translocase (Tat) pathway was first characterised in chloroplast
thylakoid membranes in the late 1990s. It has since been identified in the plasma
membranes of both Gram-positive and Gram-negative bacteria. Substrates of this
transport system contain a critical twin-arginine motif within their cleavable Nterminal
signal sequence and the majority are large co-factor containing proteins.
There is now considerable evidence that Tat systems can transport such globular
proteins in a fully folded state. The minimal components required for transport in
E.coli are TatA, TatB and TatC; these three integral membrane proteins are thought
to form an active translocon. In Bacillus subtilis only TatA and TatC subunits are
present, with TatA acting in a bifunctional manner to replace TatB. Little structural
information is known about these multimeric integral membrane protein complexes
due to the inherent difficulty in purifying them and their compositional variability.
Complexes formed by B. subtilis TatAd and TatAyCy and E. coli TatE were
investigated by single-particle EM analysis. An image processing protocol was
developed to analyse and separate out individual Tat complexes based on their size.
Using this method 3D electron density maps were generated of TatAd and TatE,
which appear as small, ring-shaped complexes. Unlike E. coli TatA complexes, that
have been shown to vary widely in size, those observed here appear small and
homogeneous. These data conflict with the widely accepted ‘size-fitting pore’ model
of Tat mediated translocation and rather support the alternative transient coalescent
model.
Additionally the first structural characterisation of a TatA-type mutant protein was
performed revealing a dramatic polymerisation phenotype and indicating a primary
role for the N-terminus in forming protein-protein interactions.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QP Physiology | ||||
Library of Congress Subject Headings (LCSH): | Membrane proteins -- Physiological transport, Escherichia coli, Electron microscopy | ||||
Official Date: | 2012 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Life Sciences | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Robinson, C. (Colin); Smith, Corinne J. | ||||
Sponsors: | Biotechnology and Biological Sciences Research Council (Great Britain) (BBSRC); Wellcome Trust (London, England) (055663/Z/98/Z) | ||||
Description: | (Published articles removed from digitised thesis for copyright reasons) |
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Extent: | 1 volume (various pagings) : illustrations. | ||||
Language: | eng |
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