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The secondary structure of a β-sheet can be described roughly by giving the number of strands, their topology, and whether their hydrogen bonds are parallel or antiparallel. β-sheets can be open , meaning that they have two edge strands (as in the flavodoxin fold or the immunoglobulin fold ) or they can be closed β-barrels (such as the TIM ...
Antiparallel and parallel beta sheet. Many proteins may adopt a beta sheet as part of their secondary structure. In beta sheets, sections of a single polypeptide may run side-by-side and antiparallel to each other, to allow for hydrogen bonding between their backbone chains. Beta sheets can also be either a parallel or anti-parallel secondary ...
A piece of paper can be formed into a cylinder by bringing opposite sides together. The two edges come together to form a line. Shear can be created by sliding the two edges parallel to that line. Likewise, a beta barrel can be formed by bringing the edges of a beta sheet together to form a cylinder. If those edges are displaced, shear is created.
E = extended strand in parallel and/or anti-parallel β-sheet conformation. Min length 2 residues. B = residue in isolated β-bridge (single pair β-sheet hydrogen bond formation) S = bend (the only non-hydrogen-bond based assignment). C = coil (residues which are not in any of the above conformations).
A beta hairpin is a common supersecondary motif composed of two anti-parallel beta strands connected by a loop. The structure resembles a hairpin and is often found in globular proteins. The loop between the beta strands can range anywhere from 2 to 16 residues. However, most loops contain less than seven residues. [2]
An alpha/beta barrel is a protein fold formed by units composed of a short α-helix followed by two anti-parallel β-strands, followed by an α-helix and a β-strand; the three β-strands form a β-sheet that runs parallel to the barrel and the α-helix is in the outside of the barrel but does not contact the α-helices of the other repeats like in TIM barrels.
Each protofilament possesses the typical cross-β structure and may be formed by 1–6 β-sheets (six are shown in the figure) stacked on each other. Each individual protein molecule can contribute one to several β-strands in each protofilament and the strands can be arranged in antiparallel β-sheets, but more often in parallel β-sheets.
The beta-propeller structure is stabilized mainly through hydrophobic interactions of the beta-sheets, while additional stability may come from hydrogen bonds formed between the beta-sheets of the C- and N-terminal ends. In effect this closes the circle which can occur even more strongly in 4-bladed proteins via a disulfide bond. [2]