Beta-Barrels
Beta-barrel from pyruvate kinase. This
enzyme has four identical subunits and each subunit has three domains.
The seven-stranded beta barrel shown here serves
as the core structure of one domain. The beta
barrel fold is found in many proteins. A single large beta
sheet twists and coils to form a closed structure in which the first strand
comes round to hydrogen bond to the last strand. The structure may be solid,
as in the barrel shown here, or it may enclose a cavity, as seen in the
next two examples.