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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 ...
Alpha-helical proteins are present in the inner membranes of bacterial cells or the plasma membrane of eukaryotic cells, and sometimes in the bacterial outer membrane. [5] This is the major category of transmembrane proteins. In humans, 27% of all proteins have been estimated to be alpha-helical membrane proteins. [6]
When the amino acids in the a and d positions were changed from I at a and L at d to I at a and I at d, a trimeric (three alpha-helices) coiled coil was formed. Furthermore, switching the positions of L to a and I to d resulted in the formation of a tetrameric (four alpha-helices) coiled coil. These represent a set of rules for the ...
The most common secondary structures are alpha helices and beta sheets. Other helices, such as the 3 10 helix and π helix , are calculated to have energetically favorable hydrogen-bonding patterns but are rarely observed in natural proteins except at the ends of α helices due to unfavorable backbone packing in the center of the helix.
A transmembrane domain (TMD, TM domain) is a membrane-spanning protein domain.TMDs may consist of one or several alpha-helices or a transmembrane beta barrel.Because the interior of the lipid bilayer is hydrophobic, the amino acid residues in TMDs are often hydrophobic, although proteins such as membrane pumps and ion channels can contain polar residues.
The cell membranes of a variety of different bacteria, fungi, animal and plant cells contain aquaporins through which water can flow more rapidly into and out of the cell than by diffusing through the phospholipid bilayer. [2] Aquaporins have six membrane-spanning alpha helical domains with both carboxylic and amino terminals on the cytoplasmic ...
A stapled peptide is a modified peptide (class A peptidomimetic), typically in an alpha-helical conformation, [2] that is constrained by a synthetic brace ("staple"). [3] The staple is formed by a covalent linkage between two amino acid side-chains, forming a peptide macrocycle. Staples, generally speaking, refer to a covalent linkage of two ...
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.