@article {4928, title = {The binding of cholera toxin to the periplasmic vestibule of the type II secretion channel.}, journal = {Channels}, volume = {5}, year = {2011}, month = {2011 May-Jun}, pages = {215-8}, abstract = {

The type II secretion system (T2SS) is a large macromolecular complex spanning the inner and outer membranes of many gram-negative bacteria. The T2SS is responsible for the secretion of virulence factors such as cholera toxin (CT) and heat-labile enterotoxin (LT) from Vibrio cholerae and enterotoxigenic Escherichia coli, respectively. CT and LT are closely related AB5 heterohexamers, composed of one A subunit and a B-pentamer. Both CT and LT are translocated, as folded protein complexes, from the periplasm across the outer membrane through the type II secretion channel, the secretin GspD. We recently published the 19 {\r A} structure of the V. cholerae secretin (VcGspD) in its closed state and showed by SPR measurements that the periplasmic domain of GspD interacts with the B-pentamer complex. Here we extend these studies by characterizing the binding of the cholera toxin B-pentamer to VcGspD using electron microscopy of negatively stained preparations. Our studies indicate that the pentamer is captured within the large periplasmic vestibule of VcGspD. These new results agree well with our previously published studies and are in accord with a piston-driven type II secretion mechanism.

}, keywords = {Bacterial Proteins, Bacterial Secretion Systems, Cholera Toxin, Periplasm, Porins, Protein Folding, Protein Structure, Protein Subunits, Protein Transport, Quaternary, Tertiary, Vibrio cholerae}, issn = {1933-6969}, author = {Reichow, Steve L and Korotkov, Konstantin V and Gonen, Melissa and Sun, Ji and Delarosa, Jaclyn R and Hol, Wim G J and Gonen, Tamir} } @article {4926, title = {Secretins: dynamic channels for protein transport across membranes.}, journal = {Trends in Biochemical Sciences}, volume = {36}, year = {2011}, month = {2011 Aug}, pages = {433-43}, abstract = {

Secretins form megadalton bacterial-membrane channels in at least four sophisticated multiprotein systems that are crucial for translocation of proteins and assembled fibers across the outer membrane of many species of bacteria. Secretin subunits contain multiple domains, which interact with numerous other proteins, including pilotins, secretion-system partner proteins, and exoproteins. Our understanding of the structure of secretins is rapidly progressing, and it is now recognized that features common to all secretins include a cylindrical arrangement of 12-15 subunits, a large periplasmic vestibule with a wide opening at one end and a periplasmic gate at the other. Secretins might also play a key role in the biogenesis of their cognate secretion systems.

}, keywords = {Bacterial Outer Membrane Proteins, Bacterial Proteins, Carrier Proteins, Gram-Negative Bacteria, Membrane Transport Proteins, Models, Molecular, Protein Binding, Protein Conformation, Protein Structure, Protein Transport, Secondary, Secretin, Tertiary}, issn = {0968-0004}, doi = {10.1016/j.tibs.2011.04.002}, author = {Korotkov, Konstantin V and Gonen, Tamir and Hol, Wim G J} } @article {3632, title = {Structure of the cholera toxin secretion channel in its closed state.}, journal = {Nature Structural \& Molecular Biology}, volume = {17}, year = {2010}, month = {2010 Oct}, pages = {1226-32}, abstract = {

The type II secretion system (T2SS) is a macromolecular complex spanning the inner and outer membranes of Gram-negative bacteria. Remarkably, the T2SS secretes folded proteins, including multimeric assemblies such as cholera toxin and heat-labile enterotoxin from Vibrio cholerae and enterotoxigenic Escherichia coli, respectively. The major outer membrane T2SS protein is the {\textquoteright}secretin{\textquoteright} GspD. Cryo-EM reconstruction of the V. cholerae secretin at 19-{\r A} resolution reveals a dodecameric structure reminiscent of a barrel, with a large channel at its center that contains a closed periplasmic gate. The GspD periplasmic domain forms a vestibule with a conserved constriction, and it binds to a pentameric exoprotein and to the trimeric tip of the T2SS pseudopilus. By combining our results with structures of the cholera toxin and T2SS pseudopilus tip, we provide a structural basis for a possible secretion mechanism of the T2SS.

}, keywords = {Amino Acid, Amino Acid Sequence, Bacterial, Bacterial Outer Membrane Proteins, Cholera Toxin, Computer-Assisted, Conserved Sequence, Cryoelectron Microscopy, Fimbriae, Image Processing, Models, Molecular, Molecular Sequence Data, Periplasm, Protein Conformation, Protein Structure, Recombinant Fusion Proteins, Sequence Alignment, Sequence Homology, Surface Plasmon Resonance, Tertiary, Vibrio cholerae}, issn = {1545-9985}, doi = {10.1038/nsmb.1910}, author = {Reichow, Steve L and Korotkov, Konstantin V and Hol, Wim G J and Gonen, Tamir} }