What is a salt bridge in the context of amino acids?

A salt bridge is a specific type of interaction that occurs between the side chains of amino acids where one has a positive charge and the other has a negative charge. This electrostatic attraction between the charged side chains stabilizes protein structures.

For example, when a positively charged amino acid, such as lysine or arginine, interacts with a negatively charged amino acid, like aspartate or glutamate, a salt bridge forms. This interaction can play a crucial role in the folding and stability of proteins, particularly in maintaining their three-dimensional structures.

In contrast to the other options, which describe different types of interactions: non-polar amino acids do not form salt bridges, as they lack charge; hydrogen bonding involves polar interactions, not specifically between charged amino acids; and hydrophobic interactions occur between non-polar amino acids in a different context, contributing to protein folding but not involving direct charge-charge interactions like salt bridges.