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| alpha helix | |
|---|---|
| Name | Alpha helix |
| Type | Secondary structure |
| First described | 1951 |
| Discoverers | Linus Pauling; Robert Corey; Herman Branson |
| Residues per turn | 3.6 |
| Rise per residue | 1.5 Å |
| Pitch | 5.4 Å |
| Handedness | Right-handed |
alpha helix is a common protein secondary structure element first described by Linus Pauling, Robert Corey, and Herman Branson in 1951. It consists of a regular right-handed helical backbone defined by hydrogen bonding patterns and characteristic geometric parameters, and appears in diverse proteins studied by groups at institutions such as University of California, Berkeley, Massachusetts Institute of Technology, and Max Planck Society. The motif is central to the structures of many proteins solved by laboratories at Royal Institution, Laboratory of Molecular Biology, and facilities like European Molecular Biology Laboratory and Brookhaven National Laboratory.
The helix is defined by repeating backbone torsion angles and unit cell dimensions determined by early crystallographers and later refined by researchers from California Institute of Technology, Harvard University, and Stanford University using data from Protein Data Bank deposits. Geometric parameters include ~3.6 residues per turn, a rise per residue of ~1.5 Å, and a pitch of ~5.4 Å; these values were validated by studies at Argonne National Laboratory and Lawrence Berkeley National Laboratory. The right-handed coil is stabilized by i → i+4 hydrogen bonds first proposed by Linus Pauling and visualized in models from Rosalind Franklin-era methods and modern cryo-EM performed at European Synchrotron Radiation Facility. Helices can be classified as α, 3_10, and π types in structural catalogs curated by Protein Data Bank and analytic frameworks developed at European Bioinformatics Institute.
Backbone hydrogen bonds form the primary stabilizing network, a concept advanced by Linus Pauling and tested in calorimetric work at National Institutes of Health laboratories. Side-chain interactions such as hydrophobic packing, salt bridges, and cation–π interactions—characterized in studies from Cold Spring Harbor Laboratory, Scripps Research, and The Scripps Research Institute—contribute additional stability. Helix dipole effects, with partial positive charge at the N-terminus and partial negative at the C-terminus, were analyzed in simulations from Princeton University, University of Chicago, and ETH Zurich. Stabilization can also derive from helix–helix packing motifs observed in membrane proteins studied by teams at Columbia University, University of Cambridge, and University of Oxford.
Sequence preferences for helix formation were quantified in large-scale surveys by groups at Uppsala University, Kyoto University, and University of Toronto, and compiled in databases maintained by UniProt and PROSITE. Alanine is a strong helix former, as shown in mutagenesis studies at Max Planck Institute for Biophysical Chemistry and Johns Hopkins University, while proline and glycine are helix breakers characterized in experiments from National Institute of Standards and Technology and European Molecular Biology Laboratory. Charged residues influence helix stability via i, i+3, i+4 interactions documented by researchers at Weizmann Institute of Science, Rudolf Magnus Institute, and Monell Chemical Senses Center. Amphipathic sequences that form helices at interfaces were defined in classic work by groups at University of California, San Diego and University of British Columbia.
Kinetic and thermodynamic studies of helix folding have been conducted using methods developed at University of Pennsylvania, University of Michigan, and University of Wisconsin–Madison. Time-resolved spectroscopy, pioneered by teams at Bell Labs and later used by groups at Max Planck Institute for Medical Research, revealed rapid helix nucleation and propagation steps. Molecular dynamics simulations from University of Illinois at Urbana–Champaign, University of Tokyo, and University of Geneva have detailed folding landscapes and transition states, while single-molecule force spectroscopy performed at Harvard Medical School and Institut Pasteur probed mechanical unfolding. Chaperone systems influencing helix formation were characterized by labs at Rockefeller University and EMBL.
Alpha helices serve diverse roles across functional proteins studied in structural biology centers such as Scripps Research Institute, Yale University, and Duke University. They form transmembrane spans in G protein–coupled receptors elucidated by teams at Global GPCR Consortium and Novartis Institutes for BioMedical Research, create recognition surfaces in transcription factors characterized at Cold Spring Harbor Laboratory and European Molecular Biology Laboratory, and mediate oligomerization interfaces in enzymes solved at Rutherford Appleton Laboratory and Lawrence Livermore National Laboratory. Helices participate in mechanical elasticity in proteins studied at Karolinska Institutet and ETH Zurich, and play catalytic or binding roles in complexes analyzed by investigators at Institut Curie and Howard Hughes Medical Institute.
Circular dichroism spectroscopy protocols standardized by groups at National Physical Laboratory and McMaster University estimate helix content, while nuclear magnetic resonance approaches developed at Bruker facilities and used by teams at University of California, San Diego provide residue-level confirmation. X-ray crystallography performed at synchrotrons such as Diamond Light Source and Stanford Synchrotron Radiation Lightsource yields atomic coordinates deposited in the Protein Data Bank. Cryo-electron microscopy advances at Max Planck Institute for Biochemistry and Thermo Fisher Scientific enable detection in large complexes. Bioinformatic prediction algorithms developed at Rost Lab, CSB (Center for Structural Biology), and European Bioinformatics Institute infer helices from sequence data archived in UniProt and validated against structures from Protein Data Bank.
Category:Protein secondary structures