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Beta-sandwich or β-sandwich domains consisting of 80 to 350 amino acids occur commonly in proteins. They are characterized by two opposing antiparallel beta sheets (β-sheets). [ 1 ] The number of strands found in such domains may differ from one protein to another. β-sandwich domains are subdivided in a variety of different folds.
Explanation of all-beta topologies: "orthogonal beta-sandwiches" are beta-barrels (as defined in this article); "aligned" beta-sandwiches" correspond to beta-sandwich folds in SCOP classification. all-beta folds in SCOP database (folds 54 to 100 are water-soluble beta-barrels).
The Rossmann fold is a tertiary fold found in proteins that bind nucleotides, such as enzyme cofactors FAD, NAD +, and NADP +.This fold is composed of alternating beta strands and alpha helical segments where the beta strands are hydrogen bonded to each other forming an extended beta sheet and the alpha helices surround both faces of the sheet to produce a three-layered sandwich.
In molecular biology, protein fold classes are broad categories of protein tertiary structure topology. They describe groups of proteins that share similar amino acid and secondary structure proportions. Each class contains multiple, independent protein superfamilies (i.e. are not necessarily evolutionarily related to one another). [1] [2] [3]
Two Rossmann folds in Cryptosporidium parvum lactate dehydrogenase, with NAD+ bound. A beta-alpha-beta motif is composed of two beta strands joined by an alpha helix through connecting loops. The beta strands are parallel, and the helix is also almost parallel to the strands. This structure can be seen in almost all proteins with parallel strands.
The C-terminal domain has an immunoglobulin-like beta-sandwich fold consisting of 9 strands in 2 sheets with a Greek key topology, similar to that found in cytochrome f and certain transcription factors. [2]
Structural studies have shown that these domains share a common core Greek-key beta-sandwich structure, with the types differing in the number of strands in the beta-sheets as well as in their sequence patterns. [2] [3] Immunoglobulin-like domains that are related in both sequence and structure can be found in several diverse protein families.
The immunoglobulin domain, also known as the immunoglobulin fold, is a type of protein domain that consists of a 2-layer sandwich of 7-9 antiparallel β-strands arranged in two β-sheets with a Greek key topology, [1] [2] consisting of about 125 amino acids. The backbone switches repeatedly between the two β-sheets.