Pi helix

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]

  1. ^ "(IUCr) Barbara Wharton Low (1920-2019)". www.iucr.org. Retrieved 2019-10-02.
  2. ^ a b Cooley 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.
  3. ^ 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.
  4. ^ 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.
  5. ^ 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.
  6. ^ 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.