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Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a generally twisted, pleated sheet. A β-strand is a stretch of polypeptide chain typically 3 to 10 amino acids long with backbone in an extended conformation .
In biology literature, the term topology is also used to refer to mutual orientation of regular secondary structures, such as alpha-helices and beta strands in protein structure [3]. For example, two adjacent interacting alpha-helices or beta-strands can go in the same or in opposite directions.
The two most common secondary structural elements are alpha helices and beta sheets, though beta turns and omega loops occur as well. Secondary structure elements typically spontaneously form as an intermediate before the protein folds into its three dimensional tertiary structure.
All beta-barrels can be classified in terms of two integer parameters: the number of strands in the beta-sheet, n, and the "shear number", S, a measure of the stagger of the strands in the beta-sheet. [3] These two parameters (n and S) are related to the inclination angle of the beta strands relative to the axis of the barrel. [4] [5] [6]
Beta-barrel proteins are so far found only in outer membranes of gram-negative bacteria, cell walls of gram-positive bacteria, outer membranes of mitochondria and chloroplasts, or can be secreted as pore-forming toxins. All beta-barrel transmembrane proteins have simplest up-and-down topology, which may reflect their common evolutionary origin ...
Porins are composed of beta sheets (β sheets) made up of beta strands (β strands) which are linked together by beta turns (β turns) on the cytoplasmic side and long loops of amino acids on the other. The β strands lie in an antiparallel fashion and form a cylindrical tube, called a beta barrel (β barrel). [2]
Small arrows on one or both of the termini, or letters. For β-strands, the direction of the arrow is sufficient. Today, the direction of the polypeptide chain is often indicated by a colour ramp. Disulfide bonds Interlocked SS symbol or a zigzag, like a stylized lightning stroke. Prosthetic groups or inhibitors Stick figures, or ball & stick ...
The individual beta strands are labeled with their traditional designations (for historical reasons, sheet A is not used), highlighting the packing of the BIDG and CHEF four-stranded sheets. [ 1 ] The jelly roll or Swiss roll fold is a protein fold or supersecondary structure composed of eight beta strands arranged in two four-stranded sheets.