What Is an Alpha Helix?

Alpha -helix is one of the main forms of protein secondary structure. Refers to the regular spiral rise of the main chain of the polypeptide chain around the central axis. Each 3.6 amino acid residues spirally rise one circle and translate 0.54 nm upwards. Therefore, the pitch is 0.54 nm and the distance between two amino acid residues is 0.15 nm . The direction of the spiral is right-handed. The R group of the amino acid side chain extends to the outside of the helix. The carbonyl oxygen of each peptide bond and the fourth NH form a hydrogen bond. The direction of the hydrogen bond is substantially parallel to the long axis of the helix. Since all peptide bonds in the peptide chain can form hydrogen bonds, the -helix is very stable.

alpha helix

-helix :

Alpha helix is one of the most common

Alpha helix cause

-helix is stable by hydrogen bonding

Factors affecting alpha helix

1. Pro (and Hpro) interrupts the -helix, producing "nodules". The -carbon atom of Pro participates in the formation of the pyrrole ring, so that the -carbon atom-N bond cannot rotate, and Gly has more freedom around the -carbon atom, so most of the -helix starts or stops at Gly, and Tyr And Ser et al.

2. Amino acids with larger side chains affect the formation of two "-carbon branches" (in addition to H on the -carbon atom, there are two other groups attached to it, such as Thr, Ile (ile), Val, etc.)

3. The amino acids with the same charge are adjacent, so that the -helix tends to disintegrate

(Overview image source)