How does pH change protein structure?
Changes in pH change the attractions between the groups in the side chains of the protein.
The interactions between the side chains of the amino acids determine the shape of a protein.
Four types of attractive interactions determine the shape and stability of a protein. The two that pH changes affect are salt bridges (a) and hydrogen bonding (b).
Salt bridges are ionic bonds between positively and negatively charged side chains of amino acids. An example is the attraction between a
Increasing the pH by adding a base converts the
Decreasing the pH by adding an acid converts the
In each case the ionic attraction disappears, and the protein shape unfolds.
Various amino acid side chains can hydrogen bond to each other. Examples are:
• Two alcohols: Ser, Thr, and Tyr.
• Alcohol and amine: Ser and Lys
• Alcohol and amide: Ser and Asn
• Alcohol and acid: Asp and Tyr
• Two acids: Asp and Glu
Changing the pH disrupts the hydrogen bonds, and this changes the shape of the protein.