Final answer:
The quaternary structure of proteins is stabilized by hydrogen bonding, ionic bonding, disulfide linkages, hydrophobic interactions, and dispersion forces. Metal ions and small molecules binding, as well as covalent bonding between specific amino acids, can also play a role in stability.
Step-by-step explanation:
The quaternary structure of proteins is held together by several types of bonds and interactions between the different subunits. These interactions are critical for the protein's stability and function. The major interactions involved in stabilizing the quaternary structure include:
- Hydrogen bonding: These are weak bonds that can form between the hydrogen atom of one amino acid and a more electronegative atom of another amino acid within the protein, or with water molecules.
- Ionic bonding: Electrostatic attractions between positively and negatively charged side chains of amino acids.
- Disulfide linkages (covalent bonds): These are strong bonds formed between sulfur atoms of two cysteine residues, which help to stabilize the overall structure.
- Hydrophobic interactions: Nonpolar side chains tend to cluster away from water, which can help drive the folding and stabilization of the protein.
- Dispersion forces: Also known as London dispersion forces, these are weak interactions that occur between nonpolar molecules or segments due to induced dipoles.
In addition to these, metal ions like Mg++ or Mn++ and small organic molecules such as heme may bind to proteins, which is important for the protein's function. Also, specific covalent bonds can form between amino acids such as cysteines after the protein has folded, further stabilizing the structure.