Quaternary Structure of Non-Conjugated and Conjugated Proteins
- Proteins with quaternary structures are composed of two or more polypeptide subunits.
- The specific three-dimensional arrangement of these subunits allows them to function as a single unit, making this level of structure essential for many biological processes.
Definition
Quartenary structure
- The quaternary structure of a protein refers to the specific three-dimensional arrangement of multiple polypeptide chains (subunits) in a single functional protein.
Non-Conjugated Proteins
Insulin
- Composed of two polypeptide chains linked by disulfide bonds.
- Its quaternary structure enables it to bind to receptors on target cells and regulate blood glucose levels.
Collagen
- Made of three polypeptide chains twisted into a triple helix.
- It provides structural support with high tensile strength, essential for skin, tendons, and ligaments.
- Collagen’s strength is further enhanced through post-translational modifications.
- For instance, proline is often converted to hydroxyproline, a change that stabilizes the triple helix.
Conjugated Proteins
Hemoglobin
- Hemoglobin is composed of four polypeptide chains, each associated with a heme group containing an iron ion (Fe²⁺).
- The heme groups bind oxygen, enabling hemoglobin to transport oxygen from the lungs to tissues and return carbon dioxide to the lungs.
- This is an example of cooperative binding:, where oxygen binding to one subunit increases the affinity of the other subunits for oxygen.
- Confusing the heme group with a polypeptide chain.
- Remember, the heme group is a non-polypeptide component essential for hemoglobin’s function.
Why Quaternary Structure Matters
- Functionality: A quarternary structuree enables proteins to perform complex tasks, such as oxygen transport (hemoglobin) or providing structural integrity (collagen).
- Disease Implications: Mutations that disrupt subunit interactions can lead to conditions like sickle cell anemia, where the quaternary structure of hemoglobin is altered.
