@article {2018|2129,
	title = {Probing the quality control mechanism of the  twin-arginine translocase with folding variants of a -designed heme protein.},
	journal = {J Biol Chem},
	volume = {293},
	year = {2018},
	month = {2018 05 04},
	pages = {6672-6681},
	abstract = {<p>Protein transport across the cytoplasmic membrane of bacterial cells is mediated by either the general secretion (Sec) system or the twin-arginine translocase (Tat). The Tat machinery exports folded and cofactor-containing proteins from the cytoplasm to the periplasm by using the transmembrane proton motive force as a source of energy. The Tat apparatus apparently senses the folded state of its protein substrates, a quality-control mechanism that prevents premature export of nascent unfolded or misfolded polypeptides, but its mechanistic basis has not yet been determined. Here, we investigated the innate ability of the model Tat system to recognize and translocate -designed protein substrates with experimentally determined differences in the extent of folding. Water-soluble, four-helix bundle maquette proteins were engineered to bind two, one, or no heme cofactors, resulting in a concomitant reduction in the extent of their folding, assessed with temperature-dependent CD spectroscopy and one-dimensional H NMR spectroscopy. Fusion of the archetypal N-terminal Tat signal peptide of the trimethylamine--oxide (TMAO) reductase (TorA) to the N terminus of the protein maquettes was sufficient for the Tat system to recognize them as substrates. The clear correlation between the level of Tat-dependent export and the degree of heme -induced folding of the maquette protein suggested that the membrane-bound Tat machinery can sense the extent of folding and conformational flexibility of its substrates. We propose that these artificial proteins are ideal substrates for future investigations of the Tat system\&$\#$39;s quality-control mechanism.</p>
},
	keywords = {Amino Acid Sequence, Bacterial Proteins, Circular Dichroism, Escherichia coli, Escherichia coli Proteins, Heme-Binding Proteins, Hemeproteins, Membrane Transport Proteins, Methylamines, Models, Molecular, Oxidoreductases, N-Demethylating, Periplasm, Protein Folding, Protein Sorting Signals, Protein Stability, Protein Transport, Proton Magnetic Resonance Spectroscopy, Substrate Specificity, Temperature},
	issn = {1083-351X},
	doi = {10.1074/jbc.RA117.000880},
	author = {Sutherland, George A and Grayson, Katie J and Adams, Nathan B P and Mermans, Daphne M J and Jones, Alexander S and Robertson, Angus J and Auman, Dirk B and Brindley, Amanda A and Sterpone, Fabio and Tuffery, Pierre and Philippe Derreumaux and Dutton, P Leslie and Robinson, Colin and Hitchcock, Andrew and Hunter, C Neil}
}
@article {2014|1645,
	title = {Type VI secretion and bacteriophage tail tubes share a common assembly pathway.},
	journal = {Embo Rep.},
	volume = {15},
	year = {2014},
	month = {mar},
	pages = {315{\textendash}21},
	abstract = {<p>The Type VI secretion system (T6SS) is a widespread macromolecular structure that delivers protein effectors to both eukaryotic and prokaryotic recipient cells. The current model describes the T6SS as an inverted phage tail composed of a sheath-like structure wrapped around a tube assembled by stacked Hcp hexamers. Although recent progress has been made to understand T6SS sheath assembly and dynamics, there is no evidence that Hcp forms tubes in vivo. Here we show that Hcp interacts with TssB, a component of the T6SS sheath. Using a cysteine substitution approach, we demonstrate that Hcp hexamers assemble tubes in an ordered manner with a head-to-tail stacking that are used as a scaffold for polymerization of the TssB/C sheath-like structure. Finally, we show that VgrG but not TssB/C controls the proper assembly of the Hcp tubular structure. These results highlight the conservation in the assembly mechanisms between the T6SS and the bacteriophage tail tube/sheath.</p>},
	keywords = {Amino Acid Sequence, Bacterial Secretion Systems, Escherichia coli, Escherichia coli Proteins, Molecular Sequence Data, Protein Binding, Protein Multimerization, Protein Structure, Tertiary, Virulence Factors},
	issn = {1469-3178},
	doi = {10.1002/embr.201337936},
	author = {Brunet, Yannick R and J{\'e}r{\^o}me H{\'e}nin and Celia, Herv{\'e} and Cascales, Eric}
}
@article {2008|1603,
	title = {Diffusion of glycerol through Escherichia coli aquaglyceroporin GlpF},
	journal = {Biophys. J.},
	volume = {94},
	number = {3},
	year = {2008},
	pages = {832{\textendash}839},
	abstract = {The glycerol uptake facilitator, GlpF, a major intrinsic protein found in Escherichia coli, selectively conducts water and glycerol across the inner membrane. The free energy landscape characterizing the assisted transport of glycerol by this homotetrameric aquaglyceroporin has been explored by means of equilibrium molecular dynamics over a timescale spanning 0.12 micros. To overcome the free energy barriers of the conduction pathway, an adaptive biasing force is applied to the glycerol molecule confined in each of the four channels. The results illuminate the critical role played by intramolecular relaxation on the diffusion properties of the permeant. These free energy calculations reveal that glycerol tumbles and isomerizes on a timescale comparable to that spanned by its adaptive-biasing-force-assisted conduction in GlpF. As a result, reorientation and conformational equilibrium of glycerol in GlpF constitute a bottleneck in the molecular simulations of the permeation event. A profile characterizing the position-dependent diffusion of the permeant has been determined, allowing reaction rate theory to be applied for investigating conduction kinetics based on the measured free energy landscape.},
	keywords = {Aquaporins, Chemical, Computer Simulation, Diffusion, Escherichia coli Proteins, Glycerol, Ion Channel Gating, Models, Molecular, Molecular Conformation, Porosity},
	doi = {10.1529/biophysj.107.115105},
	author = {J{\'e}r{\^o}me H{\'e}nin and Emad Tajkhorshid and Klaus Schulten and Christophe Chipot}
}
