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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.
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.
For example, the "globin-like" fold is described as core: 6 helices; folded leaf, partly opened. The fold to which a domain belongs is determined by inspection, rather than by software. The levels of SCOP version 1.75 are as follows. Class: Types of folds, e.g., beta sheets. Fold: The different shapes of domains within a class.
Many experimental folding studies have contributed much to our understanding, but the principles that govern protein folding are still based on those discovered in the very first studies of folding. Anfinsen showed that the native state of a protein is thermodynamically stable, the conformation being at a global minimum of its free energy.
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.
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.
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.
The fold is an elaboration on the Greek key motif and is sometimes considered a form of beta barrel. It is very common in viral proteins , particularly viral capsid proteins. [ 3 ] [ 4 ] Taken together, the jelly roll and Greek key structures comprise around 30% of the all-beta proteins annotated in the Structural Classification of Proteins ...