Membrane proteins perform a variety of functions vital to the survival of organisms:[4]
Membrane receptor proteins relay signals between the cell's internal and external environments.
Transport proteins move molecules and ions across the membrane. They can be categorized according to the Transporter Classification database.
Membrane enzymes may have many activities, such as oxidoreductase, transferase or hydrolase.
Cell adhesion molecules allow cells to identify each other and interact. For example proteins involved in immune response.