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The pitch of the alpha-helix (the vertical distance between consecutive turns of the helix) is 5.4 Å (0.54 nm), which is the product of 1.5 and 3.6. The most important thing is that the N-H group of one amino acid forms a hydrogen bond with the C=O group of the amino acid four residues earlier; this repeated i + 4 → i hydrogen bonding is the ...
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 extended structures such as the polyproline helix and alpha sheet are rare in native state proteins but are often hypothesized as important protein folding intermediates. Tight turns and loose, flexible loops link the more "regular" secondary structure elements.
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.
For example, the "unfolded" bacteriorhodopsin in SDS micelles has four transmembrane α-helices folded, while the rest of the protein is situated at the micelle-water interface and can adopt different types of non-native amphiphilic structures. Free energy differences between such detergent-denatured and native states are similar to stabilities ...
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.
Three-helix bundles are among the smallest and fastest known cooperatively folding structural domains. [1] The three-helix bundle in the villin headpiece domain is only 36 amino acids long and is a common subject of study in molecular dynamics simulations because its microsecond-scale folding time is within the timescales accessible to simulation.
An alpha-helix with hydrogen bonds (yellow dots) The α-helix is the most abundant type of secondary structure in proteins. The α-helix has 3.6 amino acids per turn with an H-bond formed between every fourth residue; the average length is 10 amino acids (3 turns) or 10 Å but varies from 5 to 40 (1.5 to 11 turns). The alignment of the H-bonds ...