An example would be cartilage, which is made of the protein collagen, and forms the nose. Functional proteins carry out a job, such as the catalysis of a chemical reaction. Functional proteins are called enzymes . For example, the metabolic enzymes break down food to provide energy. All enzymes are proteins, but not all proteins are enzymes.
Signal proteins communicate information by interacting with other proteins.
Hormones such as insulin are signal proteins. As an analogy, consider three parts of an automobile, all made of metal. A fender is part of the body of the car and would be analogous to a structural protein. The carburetor mixes gas and air and is analagous to an enzyme. The key fits into the keyhole and signals the car to start, making it analagous to a signal protein.