Alpha keratin α - keratin comes from animal hair, horns, beaks and claws. Its primary structure consists of 311-314 amino acid residues. Each alpha keratin molecule forms a typical alpha helix in the center of the peptide chain, while the two ends are non helical regions.
The helix region is composed of the HXXHCXC heptapeptide repeat sequence, which enables two α - keratin molecules to bind through the hydrophobic R group at the H position and form a double coiled helix. The stability of α - helix is greatly improved by double curly helix. In addition, several disulfide bonds are formed between the chains, which can further improve the strength of α - keratin. The strength of nails is higher than that of hair because they contain more Cys residues and can form more disulfide bonds.
α - keratin molecules can also form fibrils on the basis of double coiled spirals, and then assemble fibrils into fibers.
Permanent curl (perm) is an item Biochemical Engineering （biochemical engineering）。 α - keratin can stretch and transform into β conformation under hot and humid conditions, but it can spontaneously restore its original shape when it is cooled and dried. This is the biochemical basis for the implementation of curling technology in the beauty industry. 
Alpha keratin
