Proteins are found to have two different types of secondary structures viz. -helix and -pleated sheet structure. -helix structure of the protein is stabilised by:
(i) Peptide bonds
(ii) van der Waals forces
(iii) Hydrogen bonds
(iv) Dipole-dipole interactions
The answer is the option (iii). As these proteins are twisted in the right-hand screw fashion so each -NH group is attached to an amino acid through option (iii) Hydrogen bonds