Proteins have some structural similarity with synthetic polyamides.

Polyamides like Nylon is formed by the combination of Glycine and aminocaproic acid molecule through an amide linkage.

amide linkage

Similar amide linkage is present in protein also when two amino acids join with each other.

Peptide bond present in protein is an amide linkage.

Thus, in both proteins and synthetic polyamides amide linkage is present.