What is one of the metabolic roles of proteins?

Proteins play a crucial role in the immune system, and one of their key functions is to serve as antibodies. Antibodies, also known as immunoglobulins, are specialized proteins produced by the body in response to pathogens such as bacteria and viruses. They play an integral part in identifying and neutralizing foreign invaders, helping to protect the body from infections and diseases.

By binding to specific antigens on the surface of pathogens, antibodies help to mark them for destruction by other immune cells. This role is vital for maintaining overall health and fighting infections; without antibodies, the body's ability to defend itself against diseases would be significantly impaired.

Other options present important functions of proteins but do not specifically highlight the metabolic role of proteins in immune response as effectively. While energy storage, transport of oxygen (e.g., hemoglobin), and cell signaling are important functions of various proteins, they do not directly relate to the critical immune response facilitated by antibodies.