α-helix is spiral in shape and has a rigid arrangement of polypeptide chain as proposed by Pauling and Corey (1981). The salient features of α-helix are as follows:

1. The α-helix structure contains amino acids extending outwards from the central axis.
2. The α-helix structure is stabilised by the hydrogen bonding formed between the H atom attached to peptide N and O atom attached to peptide C. They are individually weak but together they are strong to stabilise the helix.
3. All amino acids, except the first and last ones, are involved in hydrogen bonding.
4. A single α-helix turn contains 3.6 amino acids and the distance covered by this is 0.54 nm. The space between each amino acid is 0.15 nm.
5. Low energy is utilised for the α-helix formation.
6. The stability is more for the α-helix than for the left-handed helix.
7. Proline is the only amino acid that disrupts the α-helix.

Figure 3.5 Structure of α-helix