The tertiary structure of the proteins is a three-dimensional structure. The polypeptides are arranged in a three-dimensional structure, which primarily arises because of the interaction between the side chains (R group) of the amino acids making up the protein.
The aspartic acid is a charged protein which is capable of forming the salt bridges. It can form ionic bonds with the R group of the other proteins. Hence, it can form ionic bond with the side chain of the amino acid lysine.
Hence, the answer is aspartic acid.
