Barrel channel 1-sheets

The floating-head cover is usually a circular disk. With an odd number of tube-side passes, an axial nozzle can be installed in such a floating-head cover. If a side nozzle is required, the circular disk is replaced by either a dished head or a channel barrel (similar to Fig. 11-36/) bolted between floating-head cover and floating-tube-sheet sldrt. 

Work by Stefan Matile in Geneva, Switzerland, has resulted in a number of interesting [i barrel mimetic anion transporting pores such as 12.38 (Figure 12.17).27 A [5 barrel is a kind of natural protein that forms a rigid channel by self-assembly of peptides into a /3-sheet type of secondary structure. The peptide backbone is mimicked by the rigid octaphenyl backbone which is ca. 3.4 nm long and hence spans... 

The porlns, unlike other Integral proteins, contain membrane-spanning (3 sheets that form a barrel-llke channel through the bllayer. 

Hollow structures can also be prepared by the self-assembly of stave or rod-like subunits into barrel or bundle-shaped frameworks. This is one of the most common strategies in nature for channel formation, where the rod-like molecules of the barrel-stave type are /S-sheets or a-helices of amphipathic character. The central cavity has hydrophilic properties, while the lipophilic area is oriented outward, in contact with the membrane of the cell. A natural example of this type of protein is a-hemolysin, a bacterium toxin formed by seven identical subunits that self-assemble when in contact with the cell membrane. This assembly gives rise to a mushroom-shaped structure, whose trunk is formed by a -barrel that is inserted into the cell membrane. The resulting channel has a diameter of 13 A at its narrowest point and can transport ions and other molecules. Other natural examples based on this model —but using an a-helix instead of f-sheets—include cholera toxin, potassium channels, porins, aquaporins, and the most powerful toxin known to date, botulinum neurotoxin (BoNT, known as Botox), broadly studied by Mental s group. ... 

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