What are the four types of protein?

The four main types of proteins are fibrous, globular, membrane, and conjugated proteins. Fibrous proteins, such as collagen and keratin, provide structural support and strength. Globular proteins, like enzymes and antibodies, are usually soluble and play roles in metabolic processes and immune response. Membrane proteins are involved in signaling and transport across cellular membranes, while conjugated proteins consist of amino acids combined with other non-protein molecules, enhancing their function.