Which type of interaction stabilizes the α-helix and the β-pleated sheet structures of proteins?

Hydrogen bond

Explanation:

The α-helix and the β-pleated sheet are secondary protein structures. They are formed within a polypeptide due to interactions between the atoms of the backbone.

Both the alpha helix and beta pleated sheets are held in shape (stabilized) by hydrogen bonds which form between the carbonyl (C = O) of one Amino acid and amino (N-H) of another amino acid.

This bonding is gives them their structure.