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Three-dimensional structure [1] of an alpha helix in the protein crambin. An alpha helix (or α-helix) is a sequence of amino acids in a protein that are twisted into a coil (a helix). The alpha helix is the most common structural arrangement in the secondary structure of proteins. It is also the most extreme type of local structure, and it is ...
The image above contains clickable links This diagram (which is interactive) of protein structure uses PCNA as an example. (Protein secondary structure is the local spatial conformation of the polypeptide backbone excluding the side chains. [1]
An example of an amino acid sequence plotted on a helical wheel. Aliphatic residues are shown as blue squares, polar or negatively charged residues as red diamonds, and positively charged residues as black octagons. A helical wheel is a type of plot or visual representation used to illustrate the properties of alpha helices in proteins.
Other examples of four-helix bundles include cytochrome, ferritin, human growth hormone, cytokine, [5] and Lac repressor C-terminal. The four-helix bundle fold has proven an attractive target for de novo protein design, with numerous de novo four-helix bundle proteins having been successfully designed by rational [6] and by combinatorial [7 ...
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.
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]
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.
Members share a chymotrypsin-like double β-barrel fold and similar proteolysis mechanisms but sequence identity of <10%. The clan contains both cysteine and serine proteases (different nucleophiles). [2] [32] Ras superfamily Members share a common catalytic G domain of a 6-strand β sheet surrounded by 5 α-helices. [33] RSH superfamily