Quaternary structure is stabilized by which interactions?

• A. Covalent peptide bonds
• B. Hydrogen bonds and electrostatic interactions
• C. Disulfide bonds only
• D. Ionic bonds only

Answer: (B)

Quaternary structure is the arrangement of multiple polypeptide subunits in a protein, and it is held together mainly by non-covalent interactions between those subunits. Hydrogen bonds and electrostatic (ionic) interactions provide the reversible attractions that stabilize how subunits associate, allowing the complex to form and function. Covalent peptide bonds keep each polypeptide chain intact within itself, not binding the separate subunits together, so they don’t generally stabilize the quaternary assembly. Disulfide bonds can link subunits in some proteins, but they’re not universal to all quaternary structures. Ionic bonds alone are too narrow, since hydrogen bonding also plays a major role. So, the combination of hydrogen bonds and electrostatic interactions best describes how quaternary structure is stabilized.