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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 local structure that is most easily predicted from a sequence of amino ...
Protein secondary structure is the local spatial conformation of the polypeptide backbone excluding the side chains. [1] 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 ...
A basic helix–loop–helix (bHLH) is a protein structural motif that characterizes one of the largest families of dimerizing transcription factors. [2][3][4][5] The word "basic" does not refer to complexity but to the chemistry of the motif because transcription factors in general contain basic amino acid residues in order to facilitate DNA ...
In addition to the protein domains, there are unusual transmembrane elements formed by peptides. A typical example is gramicidin A, a peptide that forms a dimeric transmembrane β-helix. [7] This peptide is secreted by gram-positive bacteria as an antibiotic. A transmembrane polyproline-II helix has not been reported in natural proteins ...
The helix-turn-helix (HTH) is a major structural motif capable of binding DNA. Each monomer incorporates two α helices, joined by a short strand of amino acids, that bind to the major groove of DNA. The HTH motif occurs in many proteins that regulate gene expression. It should not be confused with the helix–loop–helix motif.
A helix (/ ˈhiːlɪks /; pl. helices) is a shape like a cylindrical coil spring or the thread of a machine screw. It is a type of smooth space curve with tangent lines at a constant angle to a fixed axis. Helices are important in biology, as the DNA molecule is formed as two intertwined helices, and many proteins have helical substructures ...
The collagen protein is composed of a triple helix, which generally consists of two identical chains (α1) and an additional chain that differs slightly in its chemical composition (α2). [23] The amino acid composition of collagen is atypical for proteins, particularly with respect to its high hydroxyproline content.
A beta helix is a tandem protein repeat structure formed by the association of parallel beta sheet in a helical pattern with either two [1] or three [2] faces. The beta helix is a type of solenoid protein domain. The structure is stabilized by inter-strand hydrogen bonds, protein-protein interactions, and sometimes bound metal ions.