Navigation Links
Alpha helix

In proteins, the α helix is a major structural motif in secondary structure. It was first postulated by Linus Pauling, Robert Corey , and Herman Branson in 1951 based on the known crystal structures of amino acids and peptides and Pauling's prediction of planar peptide bonds.

The amino acids in an α helix are arranged in a helical structure, about 5 wide. Each amino acid results in a 100 turn in the helix, and corresponds to a translation of 1.5 along the helical axis. The helix is tightly packed; there is almost no free space within the helix. All amino acid side-chains are arranged at the outside of the helix. The N-H group of amino acid (n) can establish a hydrogen bond with the C=O group of amino acid (n+4).

Short polypeptides usually are not able to adopt the alpha helical structure, since the entropic cost associated with the folding of the polypeptide chain is too high. Some amino acids (called helix breakers) like proline will disrupt the helical structure.

Ordinarily, a helix has a buildup of positive charge at the N-terminal end and negative charge at the C-terminal end which is a destabilizing influence. As a result, α helices are often capped at the N-terminal end by a negatively charged amino acid (like glutamic acid) in order to stabilise the helix dipole. Less common (and less effective) is C-terminal capping with a positively charged protein like lysine.

α helices have particular significance in DNA binding motifs, including helix-turn-helix motifs, leucine zipper motifs and zinc finger motifs. This is because of the structural coincidence of the α helix diameter of 12 being the same as the width of the major groove in B-form DNA.

α helices are one of the basic structural elements in proteins, together with beta sheets.

The peptide backbone of an α helix has 3.6 amino acids per turn.

See also: tertiary structure -- β sheet -- collagen helix



(Date:11/2/2015)... , Nov. 2, 2015  SRI International has ... to provide preclinical development services to the National Cancer ... SRI will provide scientific expertise, modern testing and support ... of preclinical pharmacology and toxicology studies to evaluate potential ... --> The PREVENT Cancer Drug Development Program is ...
(Date:10/29/2015)... , Oct. 29, 2015  The J. Craig Venter ... titled, "DNA Synthesis and Biosecurity: Lessons Learned and Options ... of Health and Human Services guidance for synthetic biology ... --> --> ... has the potential to pose unique biosecurity threats. It ...
(Date:10/29/2015)... , Oct. 29, 2015  Rubicon Genomics, Inc., ... U.S. distribution of its DNA library preparation products, ... Rubicon,s new ThruPLEX Plasma-seq kit. ThruPLEX Plasma-seq has ... preparation of NGS libraries for liquid biopsies--the analysis ... and prognostic applications in cancer and other conditions. ...
Breaking Biology News(10 mins):
Other biology definition