Side view of a standard π-helix of L-alanine residues in atomic detail. Two hydrogen bonds to the same peptide group are highlighted in magenta; the oxygen-hydrogen distance is 1.65 Å (165 pm). The protein chain runs upwards, i.e., its N-terminus is at the bottom and its C-terminus at the top of the figure. Note that the sidechains point slightly downwards, i.e., towards the N-terminus.
A pi helix (or π-helix) is a type of secondary structure found in proteins. Discovered by crystallographer Barbara Low in 1952[1] and once thought to be rare, short π-helices are found in 15% of known protein structures and are believed to be an evolutionary adaptation derived by the insertion of a single amino acid into an α-helix.[2] Because such insertions are highly destabilizing,[3] the formation of π-helices would tend to be selected against unless it provided some functional advantage to the protein. π-helices therefore are typically found near functional sites of proteins.[2][4][5][6]
^"(IUCr) Barbara Wharton Low (1920-2019)". www.iucr.org. Retrieved 2019-10-02.
^ abCooley RB, Arp DJ, Karplus PA (2010). "Evolutionary origin of a secondary structure: π-helices as cryptic but widespread insertional variations of α-helices enhancing protein functionality". J Mol Biol. 404 (2): 232–246. doi:10.1016/j.jmb.2010.09.034. PMC 2981643. PMID 20888342.
^Keefe LJ, Sondek J, Shortle D, Lattman EE (2000). "The alpha aneurism: a structural motif revealed in an insertion mutant of staphylococcal nuclease". Proc. Natl. Acad. Sci. U.S.A. 90 (8): 3275–3279. doi:10.1073/pnas.90.8.3275. PMC 46282. PMID 8475069.
^Weaver TM (2000). "The pi-helix translates structure into function". Protein Science. 9 (1): 201–206. doi:10.1110/ps.9.1.201. PMC 2144447. PMID 10739264.
^Fodje MN, Al-Karadaghi S (2002). "Occurrence, conformational features and amino acid propensities for the pi-helix". Protein Eng. 15 (5): 353–358. doi:10.1093/protein/15.5.353. PMID 12034854.
^Mohapatra, Samar Bhallabha; Manoj, Narayanan (January 2021). "A conserved π-helix plays a key role in thermoadaptation of catalysis in the glycoside hydrolase family 4". Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics. 1869 (1): 140523. doi:10.1016/j.bbapap.2020.140523. PMID 32853774. S2CID 221358131.
A pihelix (or π-helix) is a type of secondary structure found in proteins. Discovered by crystallographer Barbara Low in 1952 and once thought to be rare...
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...
310 helix is a type of secondary structure found in proteins and polypeptides. Of the numerous protein secondary structures present, the 310-helix is the...
structures, the alpha helix and its relatives the 310 helix and the pihelix, as well as the β-helix. The amide nitrogen and oxygen atoms are too far apart...
helix angle. The helix angle can be expressed as: Helix angle = arctan ( 2 π r m l ) {\displaystyle {\mbox{Helix angle}}=\arctan \left({\frac {2\pi...
(310 helix, alpha helix, pihelix and gamma helix). This theoretical helix contains 5.1 residues per turn.However, a fully developed gamma helix has characteristics...
"Occurrence, conformational features and amino acid propensities for the pi-helix". Protein Engineering. 15 (5): 353–358. doi:10.1093/protein/15.5.353. PMID 12034854...
DNA, which eventually facilitated the correct description of the double helix structure of DNA. Owing to disagreement with her director, John Randall...
constant or continuously varying distance while moving parallel to the axis; a helix. The first definition describes a planar curve, that extends in both of...
the complement of the outside helix angle. A normal helix is a helix on the pitch cylinder, normal to the pitch helix. The pitch line corresponds, in...
the helix angle of one having the negative of the helix angle of the other; such a pair might also be referred to as having a right-handed helix and a...
instant of time, the electric field vector of the wave indicates a point on a helix oriented along the direction of propagation. A circularly polarized wave...
In mathematics, a conical spiral, also known as a conical helix, is a space curve on a right circular cone, whose floor projection is a plane spiral....
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frequency) as: f = ω 2 π = q B 2 π m {\displaystyle f={\frac {\omega }{2\pi }}={\frac {qB}{2\pi m}}} , It is notable that the cyclotron frequency is independent...
linker helix contacts the two helix-repeats which consist of four-helix bundles. The middle domain comprises an antiparallel β-strand and a short α-helix. The...
are categorized into four main classes: alpha, mu, pi, and theta. The glutathione S-transferase pi gene (GSTP1) is a polymorphic gene encoding active...
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