title: The elusive π-helix.
abstract: Central to protein architecture is the local arrangement or secondary structure of the polypeptide backbone. Thirty to forty percent of protein domains are α-helices with 3.6 residues per turn. π-Helices, in which the peptide chain is more loosely coiled (4.4 residues per turn), have also been proposed. However, such structures necessitate an energetically unfavorable ∼1Å central helical hole. We show that rather than being composed of idealized π-helices, helical regions formed from putative π-helices actually consist of a series of concatenated wide turns with unique elliptical configurations. These structures have a larger helical radius akin to that of a π-helix, but without the loss of favorable cross-core van der Waals interactions. This not only obviates the helical void, but also endows proteins with important functionalities, including metal ion coordination, enhanced flexibility and specific enzyme-substrate binding interactions.
authors.affiliation: Molecular Cardiology and Biophysics Division, Victor Chang Cardiac Research Institute, Darlinghurst, 2010 NSW, Australia. p.riek@victorchang.edu.au
authors.forename: R Peter
authors.initials: RP
authors.lastname: Riek
authors.forename: Robert M
authors.initials: RM
authors.lastname: Graham
mesh_terms: D000595:Amino Acid Sequence; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary
chemical_list: D010455:Peptides